Morphological and histochemical analyses of two human T-cell subpopulations bearing receptors for IgM or IgG

Two subpopulations of circulating human T cells forming rosettes with neuraminidase-treated sheep erythrocytes were purified on the basis of the presence of receptors for IgG (T(G) cells) or for IgM (T(M) cells), and were shown to have distinguishing morphological and histochemical characteristics T(M) cells had the general features of typical small- or medium-sized lymphocytes; most were easily identifiable by distinctive cytoplasmic accumulations, usually one and sometimes two large spots, of nonspecific and esterase activity. The larger T(G) cells had a more complex system of cytoplasmic organelles, numerous surface villous projections, and distinctive vesicles in their cytoplasm. These vesicles were lined by a unit membrane enclosing granular material of varied electron density and intravesicular distribution. The release of the vesicular contents on short-term culture of T(G) cells was inhibited by cytochalasin B. Definition of these distinguishing characteristics of T(M) and T(G) cells provides a basis for practical enumeration of these functionally distinct subpopulations of human T cells. Some of the T(G) cells were capable of endocytosis of IgG antibody-coated erythrocytes.