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

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Abstract
Two subpopulations of circulating human T [thymus-derived] cells forming rosettes with neuraminidase-treated sheep erythrocytes were purified on the basis of the presence of receptors for Ig[immunoglobulin]G (TG cells) or for IgM (TM cells), and were shown to have distinguishing morphological and histochemical characteristics. TM cells had the general features of typical small- or medium-sized lymphocytes; most were easily identifiable by distinctive cytoplasmic accumulations, usually 1 and sometimes 2 large spots, of nonspecific acid esterase activity. The larger TG 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 TG cells was inhibited by cytochalasin B. Definition of these distinguishing characteristics of TM and TG cells provides a basis for practical enumeration of these functionally distinct subpopulations of human T cells. Some of the TG cells were capable of endocytosis of IgG antibody-coated erythrocytes.