Lymphocytes

LYMPHOCYTES, lymphatic corpuscles (lymphoid cell, lymphoid element), one of the types of white blood corpuscles or leukocytes, belonging to the category of agranulocytes (see Agranulocyte) and occurring in large quantities in lymph. The lymphocyte is a round cell, most of which is occupied by a nucleus surrounded by a narrow rim of protoplasm [see separate table (Vol. XIV, p. 659-660), figs. 8, 9 and 14]. Small, medium, and large L. are distinguished. The small L., the most common form, is slightly smaller in size than an erythrocyte (7.5 µ), appears transparent in life and does not show a distinct structure; sometimes a few small granules of a lipoid nature are visible in the protoplasm (Hammar). From the smooth surface, radially thin thread-like processes may extend, thickened at the ends. By causing the cell to swell in a hypotonic solution with a small amount of HCl, and then transferring it to 0.9% NaCl, it is possible to separate a thin membrane from the surface (Brodersen). In fixed and stained preparations, the nucleus of a round shape, slightly indented or forming a fold on one side, first catches the eye; segmented, bilobed nuclei are rarely encountered [Rieder cells]. The nucleus contains a large number of large clumps of chromatin with narrow gaps between them and stains very intensely, sometimes diffusely; nucleoli are usually not visible. The protoplasm is distinctly basophilic and shows a fine reticular structure; the layer adjacent to the nucleus is stained less intensely and sometimes oxyphilic; in the indentation of the nucleus, a cell center in the form of a diplosome was occasionally seen (though rarely). Although L. are classified as agranulocytes, a small number of small grains staining with azure (azurophilic granulation) are found in their protoplasm around the nucleus (see Azurophilia); their relation to the grains visible in life has not been clarified. When stained by Altmann-Schridde method, short rods and grains that represent mitochondria are stained with fuchsin; they can be stained with janus green in a fresh preparation (Cowdry). Medium L. are slightly larger than erythrocytes and have a wider rim of protoplasm; they merge gradually into large L., reaching 15 µ, which, however, according to the opinion of most authors, do not occur in normal blood. The ratio of small, medium, and large L., according to Arneth, is 62.7:34.6:2.7. Large L. (macrophages) have relatively more protoplasm, an eccentrically located nucleus, indented on one side, with a more delicate chromatin network, as a result of which it is stained lighter and shows larger nucleoli. In contrast to the previously prevailing opinion about the immobility of L., it can now be considered proven that they are capable of ameboid movements and emigration from vessels (Ranvier, Jolly, Wolff, Vlasov and Sepp, Schridde, etc.).- The accumulation of L. in tissues in pathological cases forms the so-called small-cell or round-cell infiltration; small L. are incapable of phagocytosis. According to the teaching of Maximov, confirmed by a number of researchers (Avrorov and Timofeevsky, Bloom, Bergel, Silberberg), L. in tissues and in tissue cultures can transform into macrophages and histiocytes (polyblasts), and through their mediation also into fibroblasts; other scientists (Aschoff) deny this. The large L., according to Maximov, is identical to the primary blood cell of other unitarists (hemocytoblast of Ferrata, lymphoidocyte of Pappenheim) and is the progenitor of blood elements of both lymphoid and myeloid groups (see Hematopoiesis). Chemically, L. differ from granular leukocytes in that they do not give a positive oxidase reaction, do not undergo autolysis (see) and do not melt tissues (see Histolysis). Their characteristic feature, according to Bergel, is the ability to split fats due to the content of lipase (see); the presence of fats and lipoids in tissues causes the emigration of L.; this explains their accumulation in chronic inflammatory processes (see also Inflammation).