Evolution responds to every action, and we are not defenseless against our enemies. The dense skin itself provides good mechanical protection: if our hands are not injured, we can dig into the dirt with impunity, and the scratch will immediately become inflamed. Saliva and tears contain lysozyme, an enzyme that destroys bacterial walls. No matter how it stings in the eye when dirt or midges get into it, you can console yourself with the thought that cheeky intruders are even worse. A small inflamed scratch is likely to hurt and go away without any iodine (we will not consider terrible cases like tetanus or hepatitis B virus). The ambitious plans of microbes to capture a huge supply of moisture, proteins, fats and carbohydrates will end in failure, because inflammation is also a protective reaction, one of the mechanisms of innate or nonspecific immunity, which in one form or another is present in all multicellular organisms. Soreness, redness, fever, and swelling are all signs of military action. High temperatures are usually uncomfortable for invaders, and in addition, edema and vasodilation provide phagocytic cells that eat foreign substances with freer access to “prey.” The mechanisms of nonspecific immunity include the cytotoxic effect of the complement system, a biochemical device for piercing the membranes of enemy cells. A more advanced defensive weapon — specific, or adaptive, immunity — is available only in higher organisms, starting with jaw-mouthed fish. This is where antibodies, or immunoglobulins, come into play—Y-like protein molecules produced by lymphocytes. The upper “sticks” of Y interact with a foreign substance (antigen), binding it or marking it for destruction. Antibody molecules are also found in the lymphocyte membrane, where they play the role of receptors that recognize antigens. Scientists are faced with a bioinformatic problem here. The antibody consists of four protein chains, which, according to the Central Dogma (DNA-RNA-protein), must be encoded by certain genes. But there can be infinitely many foreign substances entering the body — such a large number of genes of immunoglobulin chains cannot fit in any genome! The contradiction was resolved by the clonal breeding theory (it was proposed by the Australian MacFarlane Burnett, who received the 1960 Nobel Prize with Peter Medawar for the discovery of artificial immune tolerance). The genes of immunoglobulins in the genomes of non-specialized cells are contained in the form of “blanks”. When B lymphocytes mature, these genes undergo rearrangements in strictly defined regions, but with an element of randomness, so that each B cell eventually synthesizes its own unique antibody, whose variable regions are ideally suited to a still unknown antigen. The encounter with this antigen (it is recognized by B-lymphocyte receptors, similar to its antibodies), as well as signals from other cells of the immune system, prompt the B-lymphocyte to multiply rapidly and synthesize antibodies. During maturation, B lymphocytes undergo strict selection — those that accidentally “target” the body’s own molecules must be destroyed. T-lymphocytes are so called because they go through the last stages of development in the thymus (and B-lymphocytes because they were first discovered in birds in the so—called fabricium sac — bursa fabricii). Their membrane also has receptors for antigens, not quite the same as antibodies, but also belonging to the family of immunoglobulins. T-helpers (“helpers”) they activate B-lymphocytes, T-killers kill the body’s own cells, infected or altered. The same is done by lymphocytes of another group, “natural killers” (NK cells, from natural killer), but their action is less specific. Adaptive (acquired) this immunity is called because the immune system has a memory. Clones of B and T lymphocytes specific to a particular antigen remain in the body, and when they encounter the same pathogen again, they begin to multiply rapidly. That’s why the secondary immune response develops faster and most people get rubella or chickenpox only once in their lives: with repeated infection, our internal army sweeps out the invader with a filthy broom before the disease manifests. Cold or flu viruses can evade a blow due to their rapid variability, so you cannot become immune to them once and for all. But infants suffer them more severely than schoolchildren and adults, who have preserved memory lymphocytes from past epidemics with antibodies suitable for at least some areas of the new viral proteins. The principle of vaccination is based on this property of the immune system. Smallpox, polio, and whooping cough are infections that can be too expensive to get to know for the first time, so it’s better to train the “army” in advance by presenting it with a weakened culture of the pathogen or individual molecules characteristic of it. It is clear how important the immune system is for us and how dangerous its weakening is with age or disease. On the other hand, an army, even stationed on its own territory, is a small joy for civilians if the soldiers forget about discipline. When the immune system begins to react to “its” molecules and cells, autoimmune diseases occur. Allergic diseases are also associated with incorrect activation of protection. Immunological discoveries have been awarded Nobel Prizes more than once: I. I. Mechnikov and Paul Ehrlich, the creators of cellular and humoral theories of immunity (1908), Rodney Porter and Gerald Edelman, who established the structure of antibodies (1972), received them. The benefits of this research for humanity are indisputable, and besides, it is really a high science. There are so many different events at the cellular and molecular level behind the “redness and burning” that the reconstruction of the Battle of Borodino seems like child’s play.

Leukocytes (white blood cells), which include cells of the immune system, are traditionally classified according to visual characteristics. The blood preparation is stained “according to Romanovsky — Giemse” with a dye containing blue azur, red eosin and methylene blue. After that, numerous bright granules appear in the cytoplasm of some cells — they were called granulocytes, and the rest of the cells, respectively, agranulocytes. Cells whose granules are stained with the acidic dye eosin are called eosinophils, cells with purple granules stained with basic azur are called basophils, and an intermediate variant is called neutrophils. A more modern way of classifying cells is by the receptors in their membrane (immunophenotyping). Lymphocytes do not differ too much “by eye”, but each group of them is characterized by a special set of receptors. Interestingly, immunophenotyping is performed using artificially produced fluorescent antibodies to these receptors. Antibodies are not only a powerful tool for protecting against diseases, but also an excellent laboratory tool. This table cannot serve as a guide for self-interpretation of the analysis results. For example, the content of eosinophils increases with pollen allergy, parasitic disease, and arthritis. Source: Elements Photo: pixfeeds.com