Synthesis, transport, dynamics and fate of cell surface Ig and alloantigens in murine lymphocytes

The major cell surface Ig on unstimulated murine B lymphocytes has been identified as IgM monomer which is probably fully exteriorized and bound to the plasma membrane noncovalently by its Fc fragment. Consistent with this concept, lymphocytes from axenic mice synthesize only IgM. Lymphocytes in culture release the IgM monomer on a fragment of plasma membrane. Evidence was accumulated, however that the vast majority of secreted Ig does not go through a cell surface phase and is secreted as 'free' molecules. In contrast to normal murine lymphocytes, surface IgM on a B lymphoblast cell line (Daudi) was not released during incubation, indicating heterogeneity among B lymphocytes regarding release. H-2 alloantigens could also be iodinated on the cell surface but were not released during incubation. Synthesis and intracellular transport of both Ig and H 2 alloantigens in lymphocytes occurs within membranes, presumably polyribosomes attached to endoplasmic reticulum and transport within vesicles until exteriorization. In contrast to Ig, however, H 2 alloantigen is not secreted. Unlike Ig, TL and H 2 alloantigens, antigenicity of thy 1 (theta) was lost in non ionic detergent. However, Thy 1 was isolated by freeze thawing ³H galactose labeled or surface iodinated thymocytes and precipitating with the corresponding congenic antiserum. It was, therefore, suggested that the Thy 1 antigenic complex is a glycolipid of glycolipoprotein. Thymocytes and T lymphocytes have little or no Ig on their surface and did not synthesize detectable amounts of Ig. It is suggested that T cells may have an antigen specific receptor other than Ig.