Textbook - BIOLOGICAL CHEMISTRY - Hubsky Y.I. - 2000

Chapter VI. BIOCHEMISTRY OF PHYSIOLOGICAL FUNCTIONS AND SPECIALIZED TISSUES

CHAPTER 30. BIOCHEMISTRY OF IMMUNE PROCESSES

The Immune System is an anatomical and functional system of higher animals and humans that performs protective Functions to maintain internal antigenic Homeostasis. Antigens are high-molecular-weight compounds that are genetically foreign to a given Organism and provoke a specific Immune Response aimed at their rejection and elimination. Antigenic properties are predominantly exhibited by Biomacromolecules—Proteins, Nucleic Acids, some Polysaccharides, and, in certain cases, synthetic polymers. Through cellular and humoral mechanisms, the immune system ensures the recognition, binding, and destruction of antigens of both infectious and non-infectious origin.

30.1. CELLULAR AND BIOCHEMICAL ORGANIZATION OF THE IMMUNE SYSTEM

A morphological synonym for the immune system is the lymphoid system. It comprises the Thymus, Spleen, Lymph Nodes, lymphatic follicles, as well as Bone Marrow and Blood lymphocytes; the total number of lymphoid Cells in the body is approximately 10¹² (R.V. Petrov, 1987). In addition to lymphocytes, numerous PROTEINS AND Peptides act as effectors of immune processes—these include IMMUNOGLOBULINS, Complement system components, Hormones, and immune mediators.

The precursors of lymphocytes are Embryonic Stem Cells of the bone marrow, which are formed during the early Cytology/cytology/21.html">Stages of intrauterine development. The following main classes of lymphocytes are distinguished:

1. T lymphocytes, which are the primary effectors of cellular Immunity. The BIOCHEMICAL BASIS OF cellular immunity reactions is the cytotoxic action against foreign cells, mediated by T-lymphocyte lysosomal Hydrolases. Furthermore, T lymphocytes participate in a complex set of reactions regulating the functional activity of B lymphocytes.

Several types (subpopulations) of T lymphocytes are distinguished:

а) T killers (T_k), or T effectors (T_e) — "killer" lymphocytes that drive Cell-mediated immunity processes. T lymphocytes destroy foreign target cells (microorganism cells, transplants) or the organism's own cells that, due to genotype alterations, have acquired antigenic properties and provoke a corresponding rejection response, such as malignant tumor cells and cells with pathological Mutations;

б) T helpers (T_h), or helper cells — cells that assist B lymphocytes. They induce the proliferation and transformation of B lymphocytes, as well as their differentiation into plasma cells, which are producers of Antibodies—immunoglobulins;

в) T suppressors (T_s) — lymphocytes that inhibit The Development of humoral and cellular immune responses, contributing to the establishment of immunological tolerance.

2. B lymphocytes, which are the effectors of humoral immunity and precursors of antibody-producing plasma cells—the main producers of antibodies (immunoglobulins). The receptors for antigens On the surface of B lymphocytes are specific surface immunoglobulins. The interaction of these surface receptors with an antigen is accompanied by the differentiation of B lymphocytes into plasma cells and Gene translocations (see Chapter 25), which lead to The formation of DNA regions responsible for the METABOLISM/31.html">Transcription of the corresponding antibodies.

3. Null lymphocytes — cells that differ from T AND B lymphocytes; this group includes cytotoxic cells and a certain fraction of killer lymphocytes, the so-called "natural killer" (NK) cells.

The immune defense system discussed above, consisting of various classes of lymphocytes, is specific to the Chemical Nature of antigens and develops through the organism's interaction with foreign macromolecules, i.e., in The process of "immunological education". There is also the innate system of non-specific immunity, or The system of non-specific defense factors of the organism, which mediates uniform cellular and biochemical reactions to any foreign antigens. Non-specific defense factors include phagocytes (tissue macrophages, blood neutrophils and monocytes), The Complement System, and numerous blood proteins: acute-phase inflammatory proteins that possess bactericidal properties and act as inhibitors of bacterial proteinases (Lysozyme, properdin, α₂-macroglobulin, α₁-proteinase inhibitor, etc.), participating in the execution of phagocytic reactions.