title: Mouse thymus-independent and thymus-derived lymphoid cells. II. Ultrastructural studies.
abstract: The ultrastructural features of B-, T-, and surface Ig(sIg)-bearing cells have been studied on cell suspensions from lymphoid organs of mice at different stages of immunization. The cells were identified by exposure to rabbit antibodies against mouse-specific lymphocyte antigens (MSLA) or brain-associated theta antigen (BAtheta) for T cells, mouse-specific bone marrow-derived lymphocyte antigens (MBLA) for B cells, and mouse Ig for sIg-bearing cells. The rabbit antibodies fixed on the cell surfaces were detected by peroxidase-labeled sheep anti-rabbit Ig antibodies or by a "bridge" technique using southern bean mosaic virus or bacteriophage T4 as the final markers. In some experiments, short-lived lymphoid cells were labeled in vivo with repeated tritiated thymidine and the ultrastructural detection of their surface antigens was combined with radioautography. MBLA+ lymphoid cells showed a whole range of ultrastructural patterns. Most were small and medium-sized lymphocytes with a clear cytoplasm containing mono- and polyribosomes, but they comprised also blasts and large cells with various amounts of endoplasmic reticulum, as well as plasma cells at different stages of maturation. sIg-bearing cells appeared to be identical with MBLA+ cells, except that sIg was less easily detectable on large blasts, and only very rarely observed on plasma cells. MSLA+ and BAtheta+ cells fell into three categories. One of them (T(1) cells) consisted of small to medium-sized lymphocytes with a clear cytoplasm and few organelles, mostly monoribosomes. A second consisted of large cells (T(2) cells) characterized by numerous polyribosomes often in a "rosette"-like pattern, occasional dark, membrane-bound granules, and a developing "filamentous network." The third, very characteristic type, (T(3) cells) was represented by dark small to medium-sized lymphocytes, usually containing large amounts of closely packed ribosomes and showing a striking accumulation of filamentous network, often condensed in large areas devoid of cell organelles. This filamentous network appeared to correspond to the cytochalasin B-sensitive system of microfilaments found in other cells and considered to be one of the contractile elements of the cell. The T(3) lymphocytes showed frequently vesicles suggestive of a strong pinocytic activity, and assumed a variety of shapes, including uropods. Evidence is presented that T(1) lymphocytes represent "virgin" T cells, T(2) "activated," and T(3) "differentiated" lymphocytes.
mesh_terms: D000818:Animals; D000956:Antigens, Viral; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology; D001666:Binding Sites, Antibody; D002462:Cell Membrane / Q000276:immunology; D003090:Coliphages / Q000276:immunology; D004721:Endoplasmic Reticulum; D007106:Immune Sera; D007114:Immunization; D007136:Immunoglobulins; D007158:Immunologic Techniques; D051379:Mice; D008808:Mice, Inbred CBA; D010544:Peroxidases; D010942:Plant Viruses / Q000276:immunology; D010950:Plasma Cells; D011817:Rabbits / Q000276:immunology; D012270:Ribosomes; D012756:Sheep / Q000276:immunology; D013601:T-Lymphocytes / Q000166:cytology* / Q000276:immunology*
chemical_list: D000956:Antigens, Viral; D007106:Immune Sera; D007136:Immunoglobulins; D010544:Peroxidases