Until the appearance of COVID-19, few people knew what antibodies were, what their implications were, etc. Now there is a lot of talk about antibodies, herd immunity, vaccines, but do you know what antibodies are? What types exist? What are their functions? Let us tell you!
Antibodies or immunoglobulins are proteins secreted by the immune system, specifically by B lymphocytes, to fight an infection affecting the body.
These antibodies act due to the presence of an antigen, which is the foreign substance that triggers the immune response.
There are different types of antibodies, which perform different protective functions, marking for other elements of the immune system to “attack” the pathogen, etc.
TYPES OF ANTIBODIES
- IgM: these are the first antibodies to be obtained in the presence of an infection. They have a large size and are found in the bloodstream. This type of antibody has low affinity for the antigen.
- IgG: These are the first antibodies produced in a secondary response to an infection. They are smaller in size and therefore can diffuse into tissues. This type of antibody is found in the blood and extracellular fluid. They carry out numerous functions including virus neutralization.
- IgA: Also smaller in size and therefore can diffuse to tissues. They are found in secretions such as milk or saliva, and in the mucosal epithelium of the intestinal, genitourinary and respiratory tract. Their main functions are the neutralization of bacterial toxins on mucosal surfaces and the neutralization of viruses.
- IgE: This type of antibody also diffuses to tissues. Very low levels can be found in blood and extracellular fluids. It stands out for binding to mast cells and basophils. They are the antibodies that mediate allergic reactions.
- IgD: They have an unknown biological function. They stand out for the differentiation of B cells.
FUNCTIONS OF ANTIBODIES
Among some of the multiple functions of antibodies, the following stand out:
- Neutralization: they inhibit the antigen binding capacity of the pathogen to the human cell.
- Opsonization: they mark the bacteria by coating them and thus make them more visible to the cells that have the capacity to phagocytose. However, not all immunoglobulins have the ability to opsonize.
- Complement activation: IgM and some IgG activate the classical complement pathway, an immune mechanism that helps fight bacteria and eliminate products of inflammation.
- Immediate hypersensitivity: This function is associated in particular with IgE through mast cells and basophils. IgE bound to these cell types, recognizes the antigen when it arrives and releases the contents of its granules where the allergic mediators are found.
- Mucosal immunity: This function is mediated by locally synthesized IgA. They are found in saliva, tears, nasal secretions, sweat, milk, etc. They are responsible for the protection of external surfaces of the body.
- Neonatal immunity: IgG are immunoglobulins that pass the placenta and are found in breast milk. They are able to enter the infant’s digestive tract and protect against possible infections.
In other words, antibodies have a multitude of functions to protect our organism from harmful external agents.
There are numerous devices that allow the detection of these antibodies against different diseases, so they can be useful to know if you are protected against a particular pathogen or if the vaccines have been effective, such as serological test.
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