Receptors for immunoglobulin isotypes (FcR) on murine T cells: I. Multiple FcR expression on T lymphocytes and hybridoma T cell clones

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Abstract
T cell receptors for the Fc portion of the various isotypes of mouse immunoglobulins (FcR) were examined by rosette formation, using as indicator cells erythrocytes coated with monoclonal antibodies of all known isotypes of serum immunoglobulins. Three populations of mouse T cells were studied: normal thymocytes, activated T cells (ATC), generated by educating thymocytes in lethally irradiated allogeneic hosts, and hybridoma T cells, derived from somatic hybridization of ATC with the FcR-negative thymoma BW.5147. We found that (a) many different FcR could be distinguished by their specificity for a single isotype or for a combination of several isotypes; (b) ATC and hybridoma T cells expressed several such receptors that, at least in cloned cells, could be demonstrated to be borne by individual cells; (c) hybridoma T cells of independent origin bore indistinguishable receptors whereas ATC expressed markedly different FcR and (d) upon overnight incubation at 37°C, immunoglobulins were found to bind onto the cell surface, even though no corresponding constitutive FcR was detected. The same was observed with hybridoma T cells and with thymocytes. It follows that a single T cell can express several FcR. Altogether, these FcR are capable of binding all known isotypes of serum immunoglobulins. They differ from one T cell to another.