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Lymphocytes

Lymphocytes are white (colorless) blood cells that develop in the lymphoid tissue and belong to the group of non-granular leukocytes (agranulocytes). The size of most lymphocytes is 7–10 microns, and those of broadly protoplasmic ones are 12–15 microns. On Romanov-Giemsa stained smears of round-shaped lymphocytes (Fig. 1-4). The round or bean-shaped nucleus, which occupies a large part of the cell, is intensely colored with individual lighter areas. The cytoplasm of lymphocytes surrounds the nucleus in the form of a narrow light-blue rim, clarifying to the nucleus. In broad lymphocyte lymphocytes, it is pale blue. Some lymphocytes contain several large cherry-red (azurophilic) kernels in the cytoplasm.

lymphocytes
Lymphocytes: 1-4 - normal human blood lymphocytes; 5 and 6 - lymphoblasts from the blood of patients with chronic lymphocytic leukemia.

Stages in the development of lymphocytes: lymphoblast (Fig. 5 and 6), a prolimpocyte and a lymphocyte. Lymphoblasts and pro-lymphocytes appear in the blood during lymphocytic leukemia. Lymphocytes play a large role in humoral immunity (see), fixing toxins and participating in the production of antibodies. They are involved in the process of rejection of transplanted tissue. The blood of healthy people contains 1,000-2,800, with an average of 1,500 lymphocytes. in 1 mm 3 (20–35%). Lymphocytosis (an increase in the number of lymphocytes) and lymphopenia (a decrease in their number) are more often relative (see Leukocyte formula), depending on the fluctuation of the number of granulocytes, and do not have diagnostic value in themselves. Absolute lymphocytosis is observed in the period of recovery from acute infectious diseases, with infectious mononucleosis, infectious lymphocytosis, lymphocytic leukemia, thyrotoxicosis , etc. Absolute lymphopenia - with radiation sickness (see), with systemic lesions of the lymphatic apparatus (generalized tuberculosis of lymph nodes, lymphogranuloma of the lymphoma, the lymphogranuloma is the case. ).

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Lymphocytes (lymph + Greek. Kytos - cell) - cells belonging to non-granular leukocytes (agranulocytes). They make up 25–30% of all white blood cells (1500–2200 in 1 mm 3 of blood). There are small (7-9 microns), medium (10-14 microns) and large lymphocytes (15-20 microns) (Fig.). In the blood of healthy adults there are mostly small lymphocytes. They have a dark nucleus containing a lot of basichromatin, located in large clumps, and a large amount of DNA. The shape of the nucleus is round, oval or bean-shaped (in small lymphocytes it is usually round). Protoplasm is located narrow rim and due to pronounced basophilia is painted in blue. In large and medium lymphocytes, the protoplasmic rim is much wider. A light perinuclear zone is located around the nucleus.

The granularity in the lymphocyte protoplasm is usually absent, and azurophilic grains of dark cherry color can be found. In electron microscopy, lymphocytes appear as round or oval cells with a homogeneous dark core and a rim of protoplasm.

The cytoplasm is not rich in cellular organelles; mitochondria are short, thick and can surround the nucleus. Lymphocytes have limited amoeboid mobility, forming short pseudopodia or taking a pear-shaped shape when moving. Cytoplasm and nucleus are involved in the movement.

Lymphocytes are formed in the lymphoid tissue (lymph nodes, spleen, tonsils, Peyer's patches, etc.). The lymphocytes of the thymus gland, apparently, differ from those formed in the lymph nodes. Lymphocytes develop from lymphoblasts. The cycle of maturation of lymphocytes has not been studied with absolute precision, but it is believed that large and medium lymphocytes are less mature than small ones. The lifespan of lymphocytes, established with the help of labeled DNA, is 100–200 days, but in the blood about 20% of cells have an age of 3-4 days.

The function of lymphocytes for a long time was unclear. It is now established that lymphocytes are involved in the formation of antibodies (along with plasma cells) when introduced into the body of a foreign protein (antigen). In this case, antibodies are formed primarily in the corresponding regional lymph nodes, and then appear in the blood. The introduction of antigens causes an increase in the number of lymphocytes and hyperplasia of the lymphoid tissue with a sharp increase in the extracts of lymph node RNA. Lymphocytes contain globulin identical to plasma gamma globulin, which is associated with the formation of antibodies. The release of antibodies from lymphocytes is apparently under the control of the pituitary-adrenal system. Lymphocytes are carriers and, possibly, the place of deposit of nucleic acids. They are involved in the destruction of toxic products of protein metabolism and play a role in the transfer of fat absorbed in the small intestine. Lymphocytes are found in the foci of inflammation, mainly chronic.

An increase in the number of lymphocytes is called lymphocytosis. There are relative lymphocytosis (percentage increase) and absolute (increase in the absolute number of lymphocytes). Most often lymphocytosis occurs in acute infectious diseases (whooping cough, infectious mononucleosis, smallpox), recovery from acute infections and intoxications, benign tuberculosis, thyrotoxicosis; with lymphatic leukemia. Relative lymphocytosis is observed in most conditions occurring with neutropenia.

A decrease in the content of lymphocytes is called lymphopenia and can occur at the onset of many acute infections, with miliary tuberculosis, and in all diseases where lymphoid tissue is replaced (lymphoma, lymphosarcomatosis).

Lymphocytes: 1-4 - normal human blood lymphocytes; 5 and 6 - lymphoblasts from the blood of patients with chronic lymphoid leukemia.