Tcr isoform containing the fc receptor chain exhibits structural and functional differences from isoform containing cd3

The structure and function of the TCR-CD3 complex containing a homodimer of the gamma chain of the high affinity receptor for IgE (FcR?) (FcR7+ TCR) was investigated by transfecting the FcR? gene into a CD3, CD3ij, FcR7 T cell line. Introduction of FCR7, as well as CD3f, induced a high expression of the TCR-CD3 complex on the cell surface. Transfected FCR7 formed a homodimer and associated firmly with the TCRa/3 dimer but only weakly with the CD375e. Stimulation of both FCR7 and CD3f transfectants by antibodies against TCR or CD3 induced accumulation of Inositol phosphates, the Ca2+ response, IL-2 production, and growth inhibition. On the other hand, antigen stimulation of transfectants expressing FCR7 as well as CD3 Induced IL-2 production, but only the latter exhibited the antigen-induced growth Inhibition. In vitro kinase assay suggested that the CD3f dimer but not the FCR7 dimer associates with the Fyn kinase. These results indicate that the FCR7 homodlmer is able to form a functional TCR complex but that the mode of assembly and the signaling function of FCR7+ TCR, including Its association with tyrosine k)nase(s), may differ from the TCR-CD3 complex containing CD3 homodimers (f+ TCR). This provides an example which Illustrates that different TCR Isoforms mediate distinct signals and functions.