A B S T R A C T Lymphocytes that bind in vitro to

Human monocytes contain two distinct receptor sites, one specific for the third component of complement (C'3), the other for immunoglobulin G(gammaG). The two receptors may function either independently or cooperatively in the induction of phagocytosis. Ingestion of erythrocytes coated with immunoglobulin M antibody requires a relatively large number of bound C'3 molecules per cell. Ingestion of erythrocytes sensitized with gammaG antibody is independent of complement; however, the reaction is inhibited by concentrations of gammaG far below those in normal serum. Inhibition by gammaG-globulin is overcome by a relatively small number of bound C'3 molecules per cell. The two monocyte receptors exert a cooperative effect on ingestion by monocytes of erythrocytes coated with gammaG antibody in the presence of inhibitory amounts of free gammaG.

A B S T R A C T Sheep red blood cells can surround, in vitro, some human peripheral blood lymphocytes in a formation called a rosette. The number of rosetteforming cells (RFC) in 50 normal persons had a wide range (4-40%).The organs of 13 human fetuses (11-19 wk conceptional age) were examined for the presence of RFC. The thymus possessed the highest percentage of RFC, the maximum being 65% of total thymocytes in two 15-16 wk fetal specimens. Blood RFC were always present and their number slightly increased in the oldest fetuses. The bone-marrow showed 0-8% in the six fetuses studied. RFC were found in the spleen around the 13th wk and in the liver around the 17th wk of gestation. These observations lead to the hypothesis that human blood RFC may be chiefly thymic derived. Studies of patients with immunological disorders support this hypothesis: one patient with Nezelof syndrome had no blood RFC and four patients with Wiskott-Aldrich syndrome had a low number of blood RFC (1 and 1.5%). Patients with acquired hypogammaglobulinemia showed a normal percentage of RFC. With the fetal thymocytes, the percentage of inhibition with anti-i, serum increased with the fetal age to become complete in the oldest fetuses studied. Incubation of the oldest fetal thymocytes or the blood lymphocytes with anti-e serum or anti-ja serulmi completely inhibited the rosette formation. These results suggest that u-chain determinants are presenit on human fetal thymocytes and blood RFC. The significance of the presence of y-chain determinants on these cells is uniclear.Presented in part at the 84th annual meetiing of the Association

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