Immunoglobulins: what are they, types, characteristics and functions?

Immunoglobulins are an important part of the immune system. Let's see how they work.

According to the Global Burden of Disease Study, 95% of the world's population has some health problem, at least in the sample group analyzed between the years 1990 and 2013. No wonder, since 15% of the world's biomass in carbon form is composed of bacteria (70 gigatons), some of them beneficial to humans, some commensal and some directly pathogenic.

Beyond bacteria, there are thousands of non-living infectious agents in the form of viruses, which mutate at a frenetic rate and evolve to circumvent the immunity of organisms in the long term. Human competition with pathogens is a veritable arms race: when a specific response to a pathogen develops, it is expected that the pathogen will eventually mutate so that it is no longer recognized by lymphocytes and other specific bodies.

For this reason, influenza vaccination campaigns are annual, whereas other vaccines provide lifelong immunity to a given pathogen. Depending on the rate of mutation and adaptability of the microorganism, the likelihood of infection may increase or decrease over time. Based on these interesting premises, we tell you everything you need to know about immunoglobulins.

What are immunoglobulins?

According to the National Cancer Institute (NIH), an immunoglobulin or antibody is a protein made by plasma cells (types of white Blood cells) in response to the presence of an antigen, a substance that causes the human immune system to become active, recognizing it as a threat.a substance that triggers the human immune system to become active, when it is recognized as a threat. The key to understanding immunity is based on the antibody (Ig)-antigen (Ag) or Ig-Ag dyad.

Each immunoglobulin binds to a single antigen, allowing specialized immune cells specialized to destroy (such as macrophages) to more effectively recognize the pathogen and phagocytose it, but but some of them can also destroy the antigen directly.. Each antibody has a specialized parasite or antigen binding site, which is specific to the epitope of the antigen itself. In other words, each Ig-Ag complex is a non-transferable key and lock.

The clearest utility of immunoglobulins in general society is undoubtedly the development of vaccines. When a weakened virus or bacterium is introduced into the body (or a section of it that promotes an immune response), it stimulates the proliferation of lymphocytes and the release of immunoglobulins specific for that antigen. Thus, the body "learns" which is the dangerous microorganism, always from the security of a previous pathogenic inactivation..

Thanks to this safe immunization mechanism, it is estimated that more than 37 million lives have been saved worldwide in the last 20 years, especially in children. A clear example of this is smallpox: in the 18th century, 400,000 people died annually from this disease, which translated into a case fatality rate of the agent of almost 30%. Thanks to vaccination, the last case of smallpox was diagnosed in 1977, and the WHO declared the world free of the pathogen in the 1980s. Undoubtedly, knowledge of immunoglobulins has enabled us as a species to rid ourselves of epidemiological havoc.

Structure of these proteins

Immunoglobulins have a typical "Y" shape, composed of two different halves. You must picturize this conformation clearly in your mind before proceeding, as we are going to rely on this pattern to describe the general conformation of antibodies.

Like all proteins, an immunoglobulin has as its basal unit the amino acid, each of the subunits which, joined by peptide bonds, gives rise to peptides (less than 10 amino acids). (less than 10 amino acids), polypeptides (more than 10) and proteins (many concatenated amino acids). In this case, the immunoglobulin type is composed of 4 polypeptide units: two heavy chains identical to each other (Heavy, at the base and cleavage of the "Y") and 2 light chains identical to each other (Light, each of the side tips of the branches of the "Y").

Each "H" region is composed of a variable region (VH) and 3-4 constant regions (CH1, CH2, CH3, etc.). On the other hand, the "L" light chains are composed of a variable region (VL) and a constant region (CL). All this may sound very confusing, but just keep in mind the following concept: the tips of the heavy (H) and light (L) chains are variable, while the overall "Y" conformation is constant among immunoglobulins of the same type.

The "Y" shape is the typical one presented in biology and immunology classes, but not the only one. This monomeric form encompasses immunoglobulins D, E and G, while Ig A is a dimer and Ig M is a pentamer. As you can imagine these anatomical changes also imply a clear variability in the functionality of the immune system..

The types of immunoglobulins

We leave the molecular forest to return to slightly more general topics, this time, the different functions of immunoglobulins according to their designation. We describe them briefly.

Immunoglobulin A

It is found in the mucous linings of the respiratory tract, the urogenital tract and the lumen of the digestive system, as well as in saliva, tears and breast milk. Interestingly, in blood it is found in a monomeric form (as the "Y" described), but in mucous membranes its arrangement is dimeric.

Due to their proximity to the only open systems within the human body (excretory, respiratory and digestive), these immunoglobulins are the first to come into contact with viruses that invade the oropharyngeal cavity and other intestinal microorganisms. are the first to come into contact with viruses that invade the oropharyngeal cavity and other intestinal microorganisms..

Immunoglobulin G

This immunoglobulin is the most represented immunoglobulin in blood, cerebrospinal fluid and peritoneal fluid (from the abdominal cavity). It constitutes 80% of the total immunoglobulins, so it is undoubtedly the most important immunoglobulin.It constitutes 80% of total immunoglobulins, so it is undoubtedly the predominant one.

In addition, it should be noted that there are 4 subvariants of this type of immunoglobulin, from IgG 1 to IgG4. Each of them is particularly adept on a particular front, detecting antigens and toxins of different microorganisms.

3. Immunoglobulin M

It is expressed on the surface of B lymphocytes, the main effectors of the humoral response of the adaptive immune system.

They are the contingency response to an infection, as they eliminate pathogens in early stages until the immune system synthesizes sufficient IgG-type s. until the immune system synthesizes sufficient IgG-type s. They account for 6% of circulating immunoglobulins in the human bloodstream. They account for 6% of circulating immunoglobulins in the human bloodstream and are present in the vast majority of animals, which is why they are considered the oldest antibodies in the evolutionary history of vertebrates.

4. Immunoglobulin E

The antibody that is clinically associated with allergic conditions. Normally, this immunoglobulin is found in small quantities circulating in the blood, but increases dramatically when the organism is exposed to an allergen, i.e., when it is exposed to an allergen.This immunoglobulin is normally found in small amounts circulating in the blood, but increases dramatically when the body is exposed to an allergen, i.e. a harmless substance that provokes an unwarranted reaction in the individual's immune system. It is also expressed in atypical quantities in the presence of parasitic infections.

5. Immunoglobulin D

This is one of the least expressed immunoglobulins, but it is no less important. It accounts for only 1% of the total immunoglobulins in the body and is the major surface component of many B-type lymphocytes in their is the major surface component of many B-lymphocytes in their maturation stage.. Due to its scarcity, its function is less well defined than that of the other variants already described.

Summary

As you may have noticed, immunoglobulins come in various forms (isotypes) and morphological arrangements, but they all have a very clear function: to protect the organism from possible infections and pathogens. From viruses to morphologically more complex parasites (such as helminths), immunoglobulins are able to recognize them, activate the other immune cells, mark them based on their surface antigens and, after the relevant cascade reaction, eliminate them.

In summary, immunoglobulins are proteins secreted by B lymphocytes and plasma cells in response to an antigen that has infiltrated the host organism. From immune responses to allergic reactions, antibodies have various protective functions.