Upon stimulation with anti-CD3, suppressor T-cell (Ts) hybridomas and homologous transfectants of T-cell receptor ai (TCRa) cDNA in the T-cell hybridoma formed a 55-kDa TCRa chain derivative that bound both the monoclonal anti-TCRa chain and polyclonal antibodies against glycosylation inhibiting factor (GIF). The peptide is a subunit of antigen-specific suppressor T-cell factor (TsF), and is considered to be a posttranslationally-formed conjugate of TCRa chain with GIF peptide. The TCRa derivative is synthesized by the transfectant after stimulation with anti-CD3, and not derived from TCR present on the cell surface. Stimulation of the stable homologous transfectants with anti-CD3 induced translocation of the 13-kDa GIF peptide into endoplasmic reticulum (ER). When a helper Ts hybridoma or a stable transfectant of the same TCRa cDNA in a helper cell-derived TCRai-clone was stimulated with anti-CD3, translocation of GIF peptide was not detected, and these cells failed to secrete a TCRa derivative. However, further transfection of a chimeric cDNA encoding a procalcitonin-GIF fusion protein into the helper cell-derived stable transfectant ofTCRai cDNA resulted in translocation of the GIF protein and formation of bioactive 55-kDa GIF. The results indicated that translocation of GIF peptide through ER is unique for Ts cells, and that this process is essential for the formation/secretion of the soluble form derivative of TCRa chain by T cells.Numerous investigators have described that antigen-specific suppressor T cells (Ts) produce soluble factors that have affinity for homologous antigen and suppress the immune response in antigen-specific manner (reviewed in refs. 1 and 2); however, little was known about the biochemical properties of the suppressor T-cell factors (TsF). In the past 5 years, however, evidence for a possible relationship between TsF and T-cell receptor (TCR) has accumulated. The monoclonal antibody (mAb) specific for the constant region of TCRa chain, H28-710, bound TsF activity from various Ts hybridomas and Ts clones (3-6). It was also found that antisense oligonucleotide corresponding to TCR Va prevented the formation of TsF activity by a Ts hybridoma (7). Kuchroo et al. (8,9) developed a series of TCRa-expression variants of Ts hybridomas, and demonstrated that transfection of TCRa cDNA from one Ts hybridoma into the TCRa-f3+ clone of another Ts hybridoma resulted in the formation of TsF activity of the former. These results collectively suggest that a product of TCRa cDNA is TsF or its subunit.Independent work in our laboratory has shown that ovalbumin-specific Ts hybridomas and bee vemon phospholipase A2-specific Ts hybridomas constitutively secrete a 13-kDa cytokine, designated glycosylation inhibiting factor (GIF), but the same cells produce GIF having affinity for homologous antigen upon antigenic stimulation or crosslinking of TCR/ CD3 (3, 10). The antigen-specific GIF suppressed in vivo antibody responses of syngeneic mice in a carrier-specific manner, indicating that the factor r...