Histology. Immunocytopoiesis and participation of immune cells in immune reactions

Lecture notes, cheat sheets
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Histology. Immunocytopoiesis and participation of immune cells in immune reactions

Lecture notes, cheat sheets

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Topic 12. IMMUNOCYTOPOIESIS AND THE PARTICIPATION OF IMMUNE CELLS IN IMMUNE REACTIONS

Unlike myelopoiesis, lymphocytopoiesis in the embryonic and postembryonic periods is carried out in stages, replacing different lymphoid organs. As noted earlier, lymphocytopoiesis is divided into:

1) T-lymphocytopoiesis;

2) B-lymphocytopoiesis.

In turn, they are divided into three stages:

1) bone marrow stage;

2) the stage of antigen-independent differentiation, carried out in the central immune organs;

3) the stage of antigen-dependent differentiation, carried out in peripheral lymphoid organs.

T-lymphocytopoiesis

The first stage is carried out in the lymphoid tissue of the red bone marrow, where the following cell classes are formed:

1) stem cells - class I;

2) semi-stem cells precursors of T-lymphocytopoiesis - class II;

3) unipotent T-poietin-sensitive cells, precursors of T-lymphocytopoiesis. These cells migrate into the bloodstream and reach the thymus (thymus) - class III.

The second stage is antigen-independent differentiation, which takes place in the thymus cortex. In this case, further formation of T-lymphocytes occurs. Stromal cells secrete thymosin, under the influence of which the transformation of unipotent cells into T-lymphoblasts occurs. They are class IV cells in T-lymphocytopoiesis. T-lymphoblasts turn into T-prolymphocytes (class V cells), and they turn into T-lymphocytes - class VI.

In the thymus, three subpopulations of T-lymphocytes develop independently from unipotent cells - T-killers, T-helpers, T-suppressors.

The resulting T-lymphocytes acquire different receptors for various antigens in the thymus cortex, while the antigens themselves do not enter the thymus. Protection of the thymus gland from the ingress of foreign antigens is carried out due to the presence of the hematothymic barrier and the absence of afferent vessels in the thymus.

As a result of the second stage, subpopulations of T-lymphocytes are formed, which have different receptors for certain antigens. The thymus also produces T-lymphocytes that have receptors for the antigens of their own tissues, but such cells are immediately destroyed by macrophages.

After the formation of T-lymphocytes, without penetrating into the thymus medulla, they enter the bloodstream and are carried to the peripheral lymphoid organs.

The third stage (antigen-independent differentiation) is carried out in T-dependent zones of peripheral lymphoid organs - lymph nodes and spleen. Here, conditions are created for the meeting of the antigen with the T-lymphocyte (killer, helper or suppressor) that has a receptor for this antigen.

Most often, there is not a direct interaction of a T-lymphocyte with an antigen, but an indirect one - through a macrophage. When a foreign antigen enters the body, it is first phagocytosed by a macrophage (completed phagocytosis), partially cleaved, and the antigenic determinant is brought to the surface of the macrophage, where it is concentrated. Then these determinants are transmitted by macrophages to the corresponding receptors of various subpopulations of T-lymphocytes. Under the influence of a specific antigen, a blastotransformation reaction occurs - the transformation of a T-lymphocyte into a T-lymphoblast. Further differentiation of cells depends on which subpopulation of T-lymphocytes has interacted with the antigen.

T-killer lymphoblast gives the following clones of cells.

1. T-killers (or cytotoxic lymphocytes), which are effector cells that provide cellular immunity. T-killers provide the primary immune response - the body's reaction to the first interaction with the antigen.

In the process of destruction of a foreign antigen by killers, two main mechanisms can be distinguished: contact interaction - the destruction of a section of the cytolemma of the target cell and distant interaction - the release of cytotoxic factors that act on the target cell gradually and for a long time.

2. T-memory cells. These cells, when the body encounters the same antigen again, provide a secondary immune response that is stronger and faster than the primary one.

T-helper lymphoblast produces the following cell clones:

1) T-helpers that secrete the mediator lymphokine, which stimulates humoral immunity. It is an immunopoiesis inducer;

2) T-memory cells.

T-suppressor lymphoblast produces the following cell clones:

1) T-suppressors;

2) T-memory cells.

Thus, during the third stage of T-lymphocytopoiesis, the formation of effector cells of each subpopulation of T-lymphocytes (T-killers, T-helpers and T-suppressors) with a certain function, and T-memory cells that provide a secondary immune response occurs.

In cellular immunity, two mechanisms can be distinguished for the destruction of target cells by killers - contact interaction, in which a section of the cytolemma of the target cell is destroyed and its death, and distant interaction - the release of cytotoxic factors that act on the target cell gradually and cause its death after a certain time .

B-lymphocytopoiesis

In the process of B-lymphocytopoiesis, the following stages can be distinguished.

The first stage is carried out in the red bone marrow, where the following cell classes are formed:

1) stem cells - class I;

2) semi-stem cells, precursors of lymphopoiesis - class II;

3) unipotent B-lymphopoietin-sensitive cells - precursors of B-lymphocytopoiesis - class III.

The second stage - antigen-independent differentiation - in birds is carried out in a special organ - the bursa of Fabricius, in mammals, including humans, such an organ has not been found. Most researchers believe that the second stage (as well as the first) is carried out in the red bone marrow, where B-lymphoblasts, class IV cells, are formed. Then they proliferate into B-prolymphocytes - class V cells and into B-lymphocytes - class VI cells. During the second stage, B-lymphocytes acquire a variety of receptors for antigens. At the same time, it was found that receptors are represented by proteins - immunoglobulins, which are synthesized in the maturing B-lymphocytes themselves, then brought to the surface and integrated into the plasma membrane. The terminal chemical groups of these receptors are different, and this explains the specificity of their perception of certain antigenic determinants of different antigens.

The third stage - antigen-dependent differentiation is carried out in B-dependent zones of peripheral lymphoid organs - in the spleen and lymph nodes. Here, B-lymphocytes meet with antigens, their subsequent activation and transformation into an immunoblast. This happens only with the participation of additional cells - macrophages, T-helpers and T-suppressors. Therefore, for the activation of B-lymphocytes, the cooperation of the following cells is necessary - a B-lymphocyte, a T-helper or a T-suppressor, as well as a humoral antigen - a bacterium, a virus, or a polysaccharide protein. The interaction process proceeds as follows: the antigen-presenting macrophage phagocytizes the antigen and brings the antigenic determinant to the surface of the cell membrane, after which the determinant acts on B-lymphocytes, T-helpers and T-suppressors. Thus, the influence of the antigenic determinant on the B-lymphocyte is not enough for the blastotransformation reaction; it proceeds after the activation of the T-helper and the release of an activating lymphokine by it. After that, the B-lymphocyte turns into an immunoblast. After the proliferation of the immunoblast, clones of cells are formed - plasmocytes - effector cells of humoral immunity, they synthesize and secrete into the blood immunoglobulins - antibodies of various classes and B-memory cells.

Immunoglobulins (antibodies) interact with specific antigens, an antigen-antibody complex is formed, thus neutralizing foreign antigens.

T-helpers play the following function in the implementation of humoral immunity - they contribute to the reaction of blastotransformation, replace the synthesis of non-specific immunoglobulins with specific ones, stimulate the synthesis and release of immunoglobulins by plasma cells.

T-suppressors are activated by the same antigens and secrete lymphokines that inhibit the formation of plasma cells and their synthesis of immunoglobulins up to complete cessation. Thus, the effect of T-killers and T-helpers on the B-lymphocyte regulates the response of humoral immunity.

Authors: Selezneva T.D., Mishin A.S., Barsukov V.Yu.

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