Innate Immunity

∞ generated and posted on 2020.03.23 ∞

Innate immunity is a means by which organisms are able to recognize and subsequently destroy smaller organisms that are invading or attempting to invade their bodies.

Innate Immunity is the means by which the body protects itself immediately, or nearly so, against especially pathogens and other infectious agents, in a manner that is more or less unchanging within a single individual over its lifespan and which involves a myriad of often interacting mechanisms; for a pathogen to be a pathogen it at a minimum must be able to evade a host organism's innate immunity.

This page contains the following terms: Infectious disease, Pathogen, Immune System Recognition, Inflammation, Innate immunity, Adaptive immunity, Antigen, Antibody, Antigen-antibody complex, Gamma globulin, Monoclonal antibody, Self antigens, Allergen, Leukocyte, Phagocyte, Monocyte, Spleen, Macrophage, Neutrophil, Eosinophil, Basophil, Mast cells, Histamine

The above provides an overview of innate immunity.

Infectious disease

Malady caused either by a microorganism or by an equivalent entity capable of both transmission between hosts and replication.
Microorganisms include bacteria, viruses, protozoa, fungi, and also parasitic worms as well as infectious proteins called prions (the latter cause such diseases as Mad Cow Disease). There also is infectious nucleic acid (RNA) that infects plants; these are called viroids. The vast majority of microorganisms, however, do not cause disease in any organisms.

With bacteria or viruses that cause infectious diseases, as well as various disease-causing fungi, we call those organisms pathogens. With protozoa that can cause disease or instead with infectious worms (helminths), we call those organisms parasites.

It is also possible describe all infectious organisms, and then some, as parasites. Not everybody conforms to this usage, however, instead limiting their use of the term parasites, among infectious agents, to disease-causing protozoa, infectious worms, and what are known as ectoparasites, such as lice.

Note that not all infectious diseases are transmittable directly between individuals. Tetanus and botulism, for example, are infectious diseases, but they are obtained from the environment rather than from affected people.

Links to terms of possible interest: Animals, Bacteria, Biotechnology, Cheeses, Ecosystem, Fermented products, Fungi, Gene cloning, Helminths, Infectious disease, Macrofungi, Microbes, Microbiomes, Microfungi, Microorganism, Microscopic, Molds, Normal flora, Normal microbiota, Nutrient cycling, Organisms, Origin of life, Parasitic worms, Pathogens, Plants, Prions, Prokaryotes, Protists, Protozoa, Sausages, Solvents, Transmission, Viruses, Yeasts, Yogurt

The above video provides a very quick introduction to the place of microorganisms within the scheme of organisms generally.

The above video provides a nice introduction to the concept of infectious disease.

The above video discusses how microorganisms are important to us as well as to our society, in both good and bad ways.


Disease-causing microorganism, and particularly a disease-causing bacterium or virus.
Pathogens are a form of parasite, though among infectious diseases, the term parasite is typically reserved for disease-causing organisms that are neither viruses, bacteria, or, for that matter, fungi.

Parasites instead are often strictly limited to disease-causing non-fungi eukaryotes. These include protozoa, helminths, and also arthropod ectoparasites. That is, single-celled eukaryotes, various parasitic worms, and insect-like animals such as mites and ticks are all parasite though strictly speaking are not typically described as pathogens

Pathogens are pathogenic, which again means that they cause diseases, and specifically they cause infectious diseases, which are diseases which both can replicate and spread to new individuals. So too, many parasites are pathogenic, such as, for example, tapeworms. Thus, whether or not one describes something as pathogenic is not fully a function of whether one describes that something also as a pathogen.

To a large extent the role of immunology and immune systems is to combat pathogens as well as many parasites, either blocking their access to our tissues or instead eliminating them from the body should such access occur. In the absence of a fully functioning immune system, however, even what should otherwise be trivial infections can become life threatening, and even otherwise non-pathogenic organisms can cause diseases.

Links to terms of possible interest: Commensalism, Ectoparasites, Eukaryotes, Fungi, Helminths, Hosts, Immune systems, Infections, Infectious diseases, Infestations, Microorganisms, Mutualism, Mycoses, Parasite, Parasitic protozoa, Parasitic worms, Parasitism, Pathogenic, Pathogenic bacteria, Pathogens, Single-celled eukaryotes, Symbionts, Tapeworms, Viral infections, Virus

The above video considers some aspects of what pathogens represent, considering a subset of bacteria that make us sick due to their production of toxins.

Immune system recognition

Binding of body molecules to foreign molecules, particular as results in changes in body physiological behavior towards that foreign molecule or towards its associated foreign organism.
These changes in behavior can be towards release of immune-response effector molecules (i.e., cytokines) or towards cell proliferation, as seen particularly with lymphocytes, a kind of white blood cell. In any case, it is the actual, physical attachment of especially an immune system receptor protein to a molecule that is consequently recognized as foreign to the body, that stimulates these changes.

The result of these processes can be signals that tell the body to ramp up its immune responses generally, particularly given recognition by innate mechanisms, or instead to ramp up its response to specific antigens, as seen with adaptive immunity. The latter results in the proliferation of specific subpopulations of lymphocytes, i.e., lymphocytes that have successfully recognized, that is, have bound to the antigen in question.

In other words, an immune response requires recognization by the body of something to respond to, ideally something that is otherwise foreign to the body, and that recognition involves the binding of an immune system molecule to a molecular aspect of a foreign organism or material.


Localized response within bodies to damage as well as to the presence of foreign materials within normally sterile tissues.
Inflammation is a response by bodies especially to injuries such as cuts or to infections, for the latter particularly localized ones. It is a means by which bodies spatially contain injuries, get infections under control, and also set things up for subsequent healing and recovery.

Inflammation involves increasing the blood and fluid supply to the injury or infection. This includes vasodilation (which is an increase in blood flow through capillaries to an area) and edema (which is increased leakage of fluids from those capillaries). Together these processes result in redness, warmth, and swelling.

Phagocytic cells also migrate to the location of this swelling, a process called chemotaxis. These cells are responsible for combatting infections which they accomplish in part by engulfing pathogens. In addition to these processes, the region undergoing inflammation becomes more sensitive to pain, which has the effect of limiting the likelihood of future trauma to the inflamed area, i.e., because that area will tend to be favored in the sense of our avoiding touching it.

Links to terms of possible interest: Bacteria, Blood flow, Capillaries, Chemotaxis, Histamine, Immune system recognition, Infection, Inflammation, Mast cells, Neutrophils, Nonspecific inflammatory response, Permeability, Phagocytic cells, Plasma, Sterile, Vasodilation, White blood cells

The above video provides a nice, fairly comprehensive overview of acute, localized inflammatory responses. Note that the term, "Emigration" (leukocyte emigration), occurs via a process known as diapedesis.

Innate immunity

Mechanisms that protect an organism from pathogens and parasites and that do not change in their specificity over the course of the organism's life span.
Innate immunity describes a large number of "hard-wired" mechanisms that your body possess which, without substantial delay, are able to interfere with the ability of another, smaller organism to harm your body. That is, interfere with the ability of that smaller, typically microorganism to cause disease, particularly infectious disease.

These mechanisms include numerous barriers (e.g., your skin as well as your gastric juices), numerous antimicrobial molecules (such as lysozyme in your tears or the free fatty acids that are found on the surface of your skin), and also numerous cell types (various leukocytes, though mostly but not entirely other than the subset of leukocytes known as lymphocytes).

What all of these processes have in common is that they do not have to substantially change following exposure to pathogens to be effective, though in many cases innate processes can be enhanced in the course of development of what is known instead as adaptive immunity. In addition, these mechanisms are so important that generally a pathogen is capable of being a pathogen within your body only if the microorganism in question possesses mechanisms that allow it to bypass or evade the numerous mechanisms that collectively are described as innate immunity.

Another way of saying this is that the vast majority of organisms on Earth, including the vast majority of microorganisms, are not capable of causing disease in you or another organism. This inability to cause disease to a large extent is because they are not proficient at dealing with innate immunity sufficiently well to succeed in causing substantial damage to the tissues that they may have become associated with.

Links to terms of possible interest: 1st line defenses, 2nd line defenses, 3rd line defenses, Adaptive immune responses, Adaptive immunity, Antibodies, Antimicrobial molecules, B lymphocytes, Basophil, Chemical barriers, Complement, Dendritic cell, Eosinophil, Fever, First-line defenses, Free fatty acids, Gastric juices, Infectious disease, Inflammation, Innate immunity, Innate immune responses, Interferon, Leukocytes, Lymphocytes, Lysozyme, Macrophage, Mast cell, Memory cells, Microbiology, Monocytes, Mucous membranes, Natural killer cells, Neutrophil, NK cells, Nonspecific defenses, Nonspecific processes, Parasites, Pathogens, Phagocytosis, Second-line defenses, Specific defenses, T lymphocytes, White blood cells

The above video provides an quick introduction to numerous aspects of innate immunity.

Adaptive immunity

Production of antibodies along with T-cell mediated cellular cytotoxicity, both as means of protecting organisms from pathogens and parasites.
The concept of adaptive immunity actually goes by a number of different names including specific immunity, acquired immunity, and even anticipatory immunity. In any case, it contrasts with what is known instead as innate immunity.

The distinction between adaptive immunity and innate immunity is one of the degree to which the body's immune system must change, following exposure to, for example, a pathogen, before the body can bring that pathogen under control; control meaning, particularly, eliminating the infecting organism from the body.

These changes take time and the reason for the delay as well as the reason that adaptive immunity is adaptive is that the immune system literally must adapt to make fundamental changes in terms of its specificity before effecting a substantial immune response.

This adaptation involves a combination of there being a huge preexisting diversity among immune system cells (specifically of lymphocytes), on the one hand, and, on the other hand, stimulation of cell division specifically of those cell variants (again, lymphocytes) that happen to recognize a target.

As noted, this particularly is an increase in the number of lymphocytes, a type of white blood cell, that is, a type of leukocyte. These lymphocytes are distinguished into B lymphocytes (or B cells), which are responsible for antibody production (a.k.a., humoral immunity), versus T lymphocytes (or T cells), which are responsible for what is known as cell-mediated immunity.

In any case, if you have become immune to a pathogen, whether following natural exposure or instead following vaccination, it is an increase in a specific subset of B cells and/or T cells that provides that immunity. The more B cells or T cells that are present that recognize a specific pathogen, and the better that they recognize that pathogen, then the stronger your immunity and resistance will be, but generally only to that specific pathogen.

Links to terms of possible interest: Acquired immunity, Active immunity, Adaptive immunity, Adaptive immune response, Antibodies, Antigens, Artificially acquired immunity, B cells, B lymphocytes, Cellular cytotoxicity, Effector T cells, Humoral immunity, Immune serum, Immune system, Immunity, Inapparent reinfection, Innate immunity, Innate immune response, Initial immune response, Lag immunity, Leukocyte, Lymphocytes, Memory immunity, Microbiology, Naturally acquired immunity, Parasites, Passive immunity, Pathogens, Placenta, Protective immune response, Specific immunity, T cell, T lymphocytes, Vaccination, Vaccines, White blood cell


Relatively complex molecules, mostly proteins but also some carbohydrates, that can be recognized by adaptive immune responses.
Key to understanding the concept of adaptive immunity is to appreciate first the concept of antigens. The idea of an antigen is simultaneously relatively simple and also somewhat complicated. The easy description is that an antigen is, at the level of individual molecules, what adaptive immune responses interact with when they recognize a target (that is, and ideally, a target molecule that is foreign to the body). These targets for immune system recognition are small sections of specific protein molecules or instead can be small sections of fairly complicated carbohydrate molecules.

It is the specific shape and chemistry of the section of these molecules that is recognized and also bound to in the course of adaptive immune responses, but it is the entire molecule containing these recognized sections that constitutes an antigen. The specific sections of these molecules that are actually being recognized instead are called epitopes or antigenic determinants.

The more complicated explanation for what an antigen is stems from just how these molecules are recognized, which differs between humoral versus cell-mediated immunity.

With humoral immunity, the antigen is recognized by a protein known as an antibody, which possesses also a small section having both a shape (conformation) and a chemistry that is complementary to the shape and chemistry of the epitope to which the antibody binds. Antibodies are diverse in their specificity such that different antibodies will tend to bind to different epitopes, and also bind with varying degrees of strength.

Far more complicated is cell-mediated immunity, where the antigen instead is a portion of a protein that has been partially digested by a cell, and then which has been presented on the surface of that cell. There it is recognized, that is, bound to by a complementary receptor molecule found on the surface of a T lymphocyte.

In either case, the antigen is a molecule that is recognized and becomes attached to – typically with substantial specificity – by a protein molecule that both is produced by a lymphocyte and which is one of a large variety of equivalent molecules that are produced by different individual lymphocytes, with one protein variety produced by each individual lineage of lymphocyte cells.

Millions of lymphocytes are present in your body, each of which produces a different variety of these protein molecules. Depending on the cell type, these antigen-binding protein molecules are called receptors (B-cell receptors or T-cell receptors) or, instead, are called antibodies.

Links to terms of possible interest: Adaptive immune responses, Antibodies, Antigen, Antigen receptor, Antigenic determinants, B-cell receptors, Cell-mediated immunity, Epitope, Humoral immunity, Immunity, Lymphocytes, Pathogens, Protein Specificities, T-cell receptors

The above video introduces the concept of antigen from the perspective of stimulation of antibody production.


Proteins produced by vertebrate animals that function by binding to other molecules, thereby either inactivating those other molecules or tagging them as foreign to the body.
Antibodies are products of white blood cells (leukocytes) that are known specifically as B lymphocytes (a.k.a., B cells). These antibodies are found in two basic forms.

One is as displayed on the surface of B lymphocyte cells and the other is suspended within extracellular fluid. The B lymphocyte-associated antibody serves as a receptor and the binding of that receptor to an antigen can stimulate the production of additional B cells via mitosis of the stimulated cells (i.e., cell division) and also the production of extracellular antibody.

Extracellular antibody comes in a variety of types dubbed IgA, IgD, IgE, IgG, and IgM, where Ig stands for immunoglobulin, which is another name for antibody. IgA is the antibody type found in secretions such as mucus while IgG is the antibody found in blood plasma. IgM tends to be produced earlier during an immune response and the other antibody types later.

Antibodies differ in their specificity, that is, what they can bind to, and this specificity varies depending on the B cell that produces them, with each B cell producing antibodies of only a single specificity.

It is as though you had a lock factory and 100 workers, each of which produced only locks that could be opened using a single pattern of key, but a pattern that is different from the keys that fit the locks produced by every other worker—a given lock will interact specifically with only a single pattern of key and a single worker will produce only locks that interact with that specific key.

Antibodies play numerous roles in immunity: They can directly inactivate other molecules such as toxin molecules. They can attach antigens to each other (crosslinking) which can glom up the ability of those antigen molecules to function as well as increase the likelihood that the associated pathogen will be engulfed by a phagocytic cell. When bound to an antigen, antibodies also can stimulate additional immune system cells such as mast cells or natural killer cells.

Links to terms of possible interest: Antibody, Antigen, Antigen-binding site, B cells, B lymphocytes, Constant domain of light chain, Constant region, COOH, Disulfide bonds, Foreign, Heavy chain, IgA, IgD, IgE, IgG, IgM, Immune system cells, Immunoglobulin, Leukocytes, Light chain, Mast cells, Mucus, Natural killer cells, NH3/sub>, nm, Polypeptides, Variable domain of light chain, Variable region, Vertebrate, White blood cells,

The above video provides a nice introduction to antibodies and their structure.

The above video introduces the concept of antibodies. Note though that antibodies do not bind to antigens or epitopes within the middle of their "Y"s, but instead at their "upper" tips. They have two such tips and therefore an ability to bind to two different epitopes per "Y".

The above video provides a nice introduction to the functioning of different classes of antibodies.

The above video provides an awe-inspiring sense of where antibody structure as well as variability come from in the course of the maturation of producing B cells (B cell maturation).

Antigen-antibody complex

The product of binding of an immunoglobulin to a protein or molecule that has been targeted by an immune response.
An antigen-antibody complex, in other words, is what results as an immediate consequence of an antibody binding to a specific antigen. The formation of an antigen-antibody complex often can be viewed as a middle step in humoral immunity, somewhere between stimulation of antibody production along with subsequent antibody release from B lymphocytes, at one end of the process, and the body acting on that binding in some manner, at the other end.

The processes that can result include the further crosslinking of antigens together, the stimulation of phagocytosis, the degranulation of mast cells, and the destruction of antibody-bound normal body cells by the lymphocytes known as natural killer cells. Formation of antigen-antibody complexes thus literally serves as the center of the process of humoral immunity, that is, antibody-mediated immunity.

Links to terms of possible interest: Agglutination, Antibody, Antibody-mediated neutralization, Antibody-mediated precipitation, Antigens, Antigen-antibody complex, Antibody-mediated immunity, B lymphocytes, Bacterium, Cell lysis, Complement system, Humoral immunity, Immune response, Immunoglobulin, Lymphocytes, Macrophage, Natural killer cells, Phagocytosis, Precipitation, Viral binding, Virus

Gamma globulin

Most common product employed for artificially acquired passive immunization.
Gamma globulin is mostly synonymous with immunoglobulin and therefore with antibody.

As a medical product, these are purified from blood, being an important component of blood serum, and can then be injected into especially immunocompromised patients. Alternatively, gamma globulins can be administered to individuals who have been exposed to specific, known pathogens to which those patients otherwise possess inadequate immunity, thereby serving as an artificial humoral immunity.

Artificially acquired passive immunization, by the way, refers to immunity that is boosted other than following natural exposure to an antigen (such as naturally occurs in the course of fighting an infection), and "passive" means that this immunization does not involve the stimulation of production of lymphocytes, i.e., as also would occur in the course of fighting a naturally acquired infection. Instead, antibodies but not their producing B cells, are artificially transfused into a patient to increase that patient's ability, over relatively short time frames, to combat infectious disease. These infused antibodies in turn are known as gamma globulins.

The above video provides an interesting dramatization regarding whether gamma globulin therapy might be warranted as well as a discussion of some of the potential downsides.

Monoclonal antibody

Immunoglobulin produced by a single lineage of cultured, immortalized plasma cells that produce a single immunoglobulin type of single, specific affinity.
When a B cell is stimulated to divide following an antigen's binding to its B cell receptors – essentially antibody-like molecules displayed on the surface of these cells – these B cells then generate, mitotically, i.e., via cell division, what is described as a clone of daughter cells (a "gaggle" of genetically identical B cells).

Each of these cells has the potential to produce antibodies, and the antibodies they produce are all of the same specificity, more or less, as those produced in receptor form by the originally stimulated B cell.

A monoclonal antibody thus is a collection of antibodies with equivalent structure and specificity that are equivalent because they are produced by a single lineage of B cells. Furthermore, and technically important, these cells are subject in the laboratory to what is known as immortalization by fusing them with myeloma cells, a type of cancer cell. This allows the resulting hybrid cells, or "hybridomas", to replicate indefinitely, that is, the cells are "immortalized" by the fusion process.

As a consequence of these efforts, one can consistently obtain antibodies of a well-defined specificity from a lineage of cells that is not subject to aging over the course of their propagation within the laboratory. The resulting monoclonal antibodies are helpful because they can serve as a means of detecting specific antigens such as in medical samples or instead can specifically attach to certain tissues within the body for targeted drug delivery, such as in the course of cancer treatment.

The antibodies found in serum are instead described as polyclonal antibodies and as a consequence can collectively possess a vast array of specificities, which is great if you are trying to generally fight pathogens, e.g., as seen with transfusion with gamma globulins, but terrible if you are trying to precisely limit what administered antibodies can interact with (e.g., normal body cells versus cancer cells).

The above video provides a nice, not highly detailed introduction to how monoclonal antibodies are generated.

The above video provides a nice though somewhat technical introduction to how monoclonal antibodies are created.

The above video provides an interesting discussion of monoclonal antibodies that in fact does *not* dwell upon specifically how they are made.

The above video provides further introduction to monoclonal antibodies with focus on applications.

The above video discusses use of monoclonal antibodies against cancer.

Self antigens

Molecule capable of inducing an adaptive immune response in another organism but not the organism that originally produced the molecule.
Antigens are antigenic, that is, are capable of inducing an adaptive immune response, i.e., they are antibody generating. A large fraction of the macromolecules produced by an organism's body have this ability to induce an adaptive immune response.

The induction of that immune response, within an organism against its own macromolecules, is in most cases suppressed, a consequence known as immunotolerance. This immunotolerance is acquired over the course of lymphocyte maturation and involves the elimination from the body of any lymphocytes that are capable of recognizing one's own macromolecules.

Potential antigens that under most circumstances are not immunogenic within the organism that produces them are described instead as self antigens. More generally, an organism's own body, and associated molecules, are described as 'self', whereas everything else, including those molecules against which an adaptive immune response under normal circumstance can occur, is known instead as 'non-self'.

When the body mistakenly immunologically attacks self molecules, i.e., self antigens, then that general pathological process is known as an autoimmune reaction or disease.


Immune-system stimulating agents particularly that result in type I hypersensitivities and associated release of histamine.
Hypersensitivities are pathological immune responses to the presence of certain antigens within the body (e.g., pollen). Type I hypersensitivity involve the antibody IgE, the white blood cells known as mast cells and basophils, though eosinophils can be involved as well, and the release of the vasodilating chemical known as histamine.

The result of IgE binding to an allergen along with subsequent degranulation such as of associated mast cells, is the release of histamine and consequent allergy symptoms. Allergens typically are proteins that in some manner fool the body into reacting with them as though they were associated with multicellular parasites such as a parasitic worm.

The above video provides a nice introduction to what allergies represent such as pollen allergies.

The above video does a good job of introducing the concept of allergies and desensitization, though the discussion is provided at a moderately high level of complexity.

The above video provides a not terribly technical introduction to allergies and then allergen immunotherapy at 2:13.

The above video provides an introduction more to allergies than to food allergens, though still does place some emphasis on the latter.


White blood cell.
There are a number of cell types that are classified under the heading of leukocyte. These include neutrophils, eosinophils, basophils, mast cells, phagocytes (including neutrophils, monocytes, and macrophages), and lymphocytes (which include B cells, T cells, and natural killer cells).

Leukocytes are all formed within your bone marrow in parallel with the development of red blood cells and platelets. The T cells (a.k.a., T lymphocytes), however, then move to your thymus where their maturation occurs. The B cells and T cells in particular effect adaptive immunity.

Links to terms of possible interest: B cells, B lymphocytes, Basophils, Bone marrow, Common lymphoid progenitor, Common myeloid progenitor, Eosinophils, Erythrocytes, Formed elements, Hemocytoblast, Hematopoietic stem cells, Immunity, Large granular lymphocyte, Leukocytes, Lymphocytes, Macrophages, Mast cells, Megakaryocytes, Monocytes, Multipotent, Multipotential hematopoietic stem cells, Myeloblasts, Natural killer cells, Neutrophils, Phagocytes, Plasma cells, Platelets, Red blood cells, Small lymphocytes, T cells, T lymphocytes, Thrombocytes, Thymus, White blood cell

A nice overview of what cells make up the white blood cells and where they come from.

The above, brief video initiates the story of white blood cells and where they come from.

The above video discusses the developmental origin of leukocytes from hematopoietic stem cells.

The above video continues the discussion of where leukocytes come from.

The above video, in addition to introducing formed elements generally, provides an introduction to general functional categories of leukocytes.

The above video is the last in this series and serves as a general introduction to leukocytes.


Leukocyte capable of removing particles, microorganisms, and debris from extracellular environments within animal bodies.
Phagocytic cells are so named for their ability to phagocytize, that is, to engulf cells as well as various clumps of things such as debris or linked together viruses. There are two major types of phagocytes within our bodies called neutrophils versus monocytes/macrophages, with the latter different stages of development of the same cell type (see as well what are known as dendritic cells).

The process of phagocytosis by phagocytes involves a combination of binding/recognition of the to-be-engulfed organism or material, the engulfing/phagocytosis process, and the subsequent digestion of the engulfed material. In this way, invading organisms or clumps of material can be removed from tissues and then destroyed.

Links to terms of possible interest: Animal, Antigen presentation, Bacterium, Digestive enzymes, Extracellular, Extracellular environments, Foreign antigens, Intracellular, Intracellular digestion, Leukocytes, Lysosome, Macrophages, Microorganisms, Monocytes, Neutrophils, Organelle, Phagocytes, Phagocytic cells, Phagocytize, Phagocytosis, Phagolysosomes, Phagosome, Receptors, Self antigens

The above video provides an introduction to phagocytes and also antigen presentation.


Immature macrophage and dendritic cells.
Monocytes make up a moderately large fraction of the white blood cells (leukocytes) that are found within the body and also are the largest of the leukocytes in terms of cell size. They serve as the source of macrophages that are normally present in specific locations within bodies, and also serve as the source of macrophages that are required to effect immune responses in the course of inflammatory responses.

Both monocytes and their descendant macrophages are phagocytic cells. The shorter-lived neutrophils are also phagocytes but by contrast are not descendants of monocytes.

A subset of dendritic cells, by contrast, are derived from monocytes. One of the functions of the spleen is to serve as a monocyte-storage organ.

Links to terms of possible interest: Amoeboid, Antigen presentation, Dendritic cells, Inflammatory responses, Leukocytes, Macrophages, Monocytes, Neutrophils, Phagocytes, Phagocytic cells, White blood cells

The above video considers especially the role of macrophages in antigen presentation.


Lymphoid organ found in the ventral cavity of vertebrates that functions to regulate various aspects of blood.
The spleen in humans is found overlain by the stomach (i.e., it is inferior to the stomach). It serves as a storage organ for red blood cells (erythrocytes) as well as for monocytes. These cells are then released as needed, such as following blood loss (particularly in the case of erythrocytes) or given substantial inflammation (in the case of monocytes).

The spleen is also responsible for the breaking down of old erythrocytes, the breaking down of the polypeptide portion of hemoglobin, the metabolism of associated heme, and the recycling of the also associated iron ion.

Related to that function, the spleen is also the effector of what is known as the mononuclear phagocytic system, which filters the blood of relatively large, undesired components via phagocytic mechanisms (versus the kidneys, which filter blood of relatively small undesired components via the glomeruli, etc.). Overall, the spleen can be viewed as the lymphoid organ of the blood, contrasting lymph nodes which serve instead as the lymphoid organs of lymph.

Links to terms of possible interest: Artery of pulp, Capillary, Capsule, Connective tissue, Erythrocytes, Heme, Hemoglobin, Inferior, Lymph nodes, Lymphocytes, Lymphoid organ, Monocytes, Mononuclear phagocyte system, Non-self antigens, Phagocytic, Red pulp, Spleen, Splenic artery, Splenic vein, Stomach, Venous sinus, Ventral cavity, White pulp

The above video takes a quick look at the structure and function of the spleen. Note that when mention is made of the production of lymphocytes, what is being referred to is the expansion of specific clones in response to interaction with non-self antigens. In addtion, when mention is made of "engulfing", the cells doing the engulfing are macrophages rather than the mentioned lymphocytes.


Long-lived phagocytic leukocytes that also serve as antigen-presenting cells.
Macrophages are derived from monocytes, which differentiate into macrophages within either normal or inflamed tissues. In normal tissues, the macrophages form into what are termed as resident macrophages. The job of these cells is to be present within tissues should a localized, macrophage-mediated immune response need to be initiated, e.g., such as following a cut and subsequent contamination of tissues with microorganisms.

In addition to their roles as phagocytes as well as effectors of localized immune responses – they detect signals associated with potential pathogens and chemically broadcast "danger" signals which serve to develop further immune responsemacrophages also serve as antigen-presenting cells, or APCs. Here phagocytized material is processed into smaller antigens within macrophages and these are then presented on the surface of the same macrophage (so too this task is accomplished by dendritic cells).

These surface-associated molecules serve as signals to lymphocytes known as T helper cells, which are responsible for stimulating yet further immune responses, particularly those of adaptive immunity.

Links to terms of possible interest: Antigens, Antigen presentation, Antigen-presenting cells, Autoimmunity, Bacteria, Dendritic cells, Immune responses, Immunity, Inflammation, Inflammatory response, Leukocytes, Lymphocytes, Lysosomes, Macrophages, Microorganisms, Monocytes, Pathogens, Phagocytic, Phagocytized, Pseudopodia, Rough ER, T helper cells, Toxins, Vesicles

The above video discusses inflammation and the role of macrophages in inflammatory responses as well as antigen presentation by macrophages; it ends with discussion of autoimmunity.

The above video discusses as well as distinguishes among monocytes, macrophages, and dendritic cells; it doesn't do a terribly good job of describing the associated antigen presentation, however.


Relatively short-lived phagocytic leukocytes.
Neutrophils are also known as neutrophil granulocytes, reflecting the presence of numerous vesicles in their cytoplasms (hence, granulocytes) in combination with their staining characteristics during microscopy (which is "neutral"). Neutrophils are also described as polymorphonuclear leukocytes, or PMNs, though neutrophils are only the most abundant of PMNs.

Neutrophils have the distinction of being the most abundant of leukocytes, that is, of white blood cells. Their role in immunity is as phagocytes, and the granules in their cytoplasms play roles in phagocytosis along with the killing of phagocytized organisms, particularly bacteria.

Neutrophils are all about this killing, living only about at most two days on average, even absent an immune response. They are capable of chemotaxis (movement towards sites of inflammation), diapedesis (movement from within the blood to outside of the blood such as to reach sites of inflammation), and also are the dominant cells found in as well as giving rise to the color of pus.

Links to terms of possible interest: Bacteria, Bone marrow, Chemotaxis, Diapedesis, Granulocytes, Immune responses, Inflammation, Leukocytes, Light microscopy, Neutrophil, Neutrophil granulocytes, Phagocytes, Phagocytic, Phagocytosis, Pus, Vesicles, White blood cells

Neutrophil functioning is considered in the above video including in terms of phagocytosis

The above video is of a fairly spectacular light microscopy movie of a neutrophil chasing and then engulfing bacteria.


Anti-parasite leukocyte that is capable of phagocytosis but which functions predominantly extracellularly, delivering toxic substances to helminths.
Eosinophils are also known as eosinophil granulocytes, reflecting the presence of numerous vesicles in their cytoplasms (hence, granulocytes) in combination with their staining characteristics by the red dye, eosin.

Eosinophils are particularly important as effectors of immune responses against multicellular parasites, particularly parasitic worms (a.k.a., helminthes). Certain allergens, e.g., pollen, can mimic multicellular parasites in terms of eosinophils response and this can lead to symptoms of allergies.

The above video describes the cellular morphology of eosinophils.


Histamine-producing leukocytes that play roles in both inflammation and allergies.
Basophils are also known as basophil granulocytes, reflecting the presence of numerous vesicles in their cytoplasms. Hence they are described as a type of granulocyte, and also reflecting their propensity to be stained for microscopy with basic dyes. Among the granulocytesneutrophils, eosinophils, mast cells, and basophilsbasophils are the least prevalent within the body.

Like eosinophils, basophils are important effectors of immune responses against multicellular parasites. Also like eosinophils, basophils often are involved in allergic reactions, such as against pollen. Basophils in particular respond to the binding of IgE antibodies to antigens

The binding as well as production of these IgE antibodies can be blocked by causing IgG production instead, which is why treatment of patients with allergens, in allergen immunotherapy/desensitization, can have the perverse result of interfering with future allergic reactions.

Towards locally increasing blood flow, basophils release the anticoagulant heparin as well as the vasodilator, histamine. The latter, histamine, is an important effector of symptoms associated with allergies and is the reason that antihistamine drugs can be effective against those symptoms.

The above video describes the cellular morphology of basophils.

Mast cells

Leukocyte that resides in tissues, releasing various chemicals leading to inflammation, particularly histamine.
Mast cells are confusing due to a close resemblance in their characteristics to those of basophils. Thus, like basophils, mast cells play roles in allergies, though also are important, in their normal role, in protection from pathogens. Like basophils, mast cells can be stimulated to degranulate and thereby release, e.g., histamine but also heparin, via their binding to IgE antibodies that then bind to an antigen molecule.

That is, mast cells possess an IgE receptor and IgE proteins otherwise bind as antibodies to specific antigens. Keep in mind that antibodies are large proteins and further that only a small, though well-defined portion of a given antibody is directly involved in antigen binding, so there is lots of especially non-variable aspects of antibody molecules that other body molecules and thereby body cells can bind to.

Mast cells, however, differ from basophils in terms of their locations of action, with mast cells found within tissues (i.e., other than blood) and with basophils residing in blood when not involved in effecting an immune response.

The above video provides an introduction to mast cells, with mention also of what are known as auxiliary cells.


Molecule playing a variety of roles in physiology, especially contribution to inflammatory responses but also playing roles in the regulation of the gastrointestinal tract as well as serving as a neurotransmitter.
Histamine, as an immune-system effector, is produced and released by basophils, eosinophils, and mast cells. The process of histamine release by these cells is a kind of degranulation, that is, the release of histamine from granules (vesicles) that otherwise are located within the cytoplasm of these cells.

This degranulation results, for example, from the binding of IgE antibody. This antibody, in other words, becomes bound to the surface of mast cells, as well as basophils, and its binding to antigens – via these antibody's other end(s) while also cell bound – results in degranulation of mast cells or basophils and an associated release of histamine.

The result is histamine contribution to inflammatory responses, though when mediated against allergens such as pollen, the results instead are the symptoms of allergies. As a consequence, antihistamine drugs can be employed to combat allergy symptoms.

The above video does a good job both describing what histamine is and its role in the body's allergic responses.