Cellular mechanisms for the formation of a soluble form derivative of T-cell receptor alpha chain by suppressor T cells.

Abstract

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...

High-affinity binding of bioactive glycosylation-inhibiting factor to antigen-primed T cells and natural killer cells

“…Evidence has been presented that bioactive GIF is a subunit of antigen-specific Ts factors (25,26). The high affinity of bioactive GIF for antigen-primed Th cells suggests that the Ts factors may bind to Th cells through GIF and exert their immunoregulatory effects.…”

Conversion of inactive glycosylation inhibiting factor to bioactive derivatives by modification of a SH group

“…We have previously described glycosylation inhibiting factor (GIF), a 13-kDa cytokine, as a product of suppressor T (Ts) cells (1,2) and a subunit of antigen-specific Ts cell factors (3,4). After molecular cloning of this cytokine, however, we realized that various cell line cells produced the 13-kDa peptide, which reacted with polyclonal antibodies against recombinant GIF (rGIF).…”

Posttranslational modification of the glycosylation inhibiting factor (GIF) gene product generates bioactive GIF

“…W e have previously described glycosylation inhibiting factor (GIF), 13-kDa cytokine, as a product of suppressor T (Ts) cells (1,2) and a subunit of antigen (Ag)-specific Ts cell factor (3,4). Repeated injections of partially purified GIF into BDF1 mice resulted in suppression of both IgE and IgG antibody (Ab) responses to ovalbumin (OVA) (5).…”