CELL SURFACE IMMUNOGLOBULIN : V. RELEASE FROM MURINE SPLENIC LYMPHOCYTES

Turnover and release of cell surface Ig and secretion of total intracellular Ig has been studied in small lymphocytes from normal mouse spleen. The major findings to emerge are: (a) small lymphocytes secrete 8S IgM and IgG. A small portion of the 8S IgM, but virtually none of the IgG appears to have a cell surface phase. (b) Cell surface IgM is actively turned over with a half-life of 6–8 hr, and turnover can be accounted for by release into the incubation medium. Release is temperature dependent. (c) Released cell surface Ig is noncovalently bound to a fragment of plasma membrane. (d) H-2 antigens are not released during short-term incubation. Based on the above findings, we propose a model for the transport and release of both cell surface and conventionally secreted Ig

CELL SURFACE IMMUNOGLOBULIN : IX. A NEW METHOD FOR THE STUDY OF SYNTHESIS, INTRACELLULAR TRANSPORT, AND EXTERIORIZATION IN MURINE SPLENOCYTES

A new method for the detection of cell surface immunoglobulin labeled with isotopic precursors is described. The method consists of the aggregation of surface Ig on cells with specific antibody (heterologous) and the subsequent removal of antigen-antibody complexes by the combination of high speed centrifugation and immunoprecipitation of remaining soluble complexes using antibody to the heterologous Ig. Using this method, the kinetics of appearance of cell surface Ig and its turnover were studied in murine splenocytes. The results suggest that cell surface Ig is synthesized and transported in the same manner as secretory Ig rather than being synthesized on the plasma membrane. The turnover of intracellular and cell surface Ig in lymphocytes is slow. In contrast, intracellular Ig in plasma cells is rapidly secreted and usually without a cell surface phase. Cell surface Ig was shown to be radiolabeled with [3H]glucosamine, -galactose, and -fucose. The proportion of cell surface to intracellular (nonsurface) Ig labeled with these precursors suggests the same sequence of addition of sugars to Ig destined to be on the surface of lymphocytes as with Ig which will be secreted by plasma cells. Results with this new method also confirm earlier conclusions based on experiments using cell surface iodination: 8S IgM is the predominant Ig on the surface of murine splenocytes and the molecule appears to be attached by its µ-chains