TCR-alpha chain-like molecule is involved in the mechanism of antigen-non-specific suppression of a ubiquitin-like protein.

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Although existence of suppressor T cells is a controversial issue in cellular immunology, several lines of evidence indicate that T-cell-receptor alpha-chain (TCR-alpha) is a critical component of suppressor factors produced by these cells. Monoclonal non-specific suppressor factor (MNSF), a lymphokine produced by murine T-cell hybridoma, possesses pleiotrophic antigen-non-specific suppressive functions. Recently, we have shown that the 70,000-MW MNSF comprises an 8000-MW ubiquitin-like polypeptide and other subunit(s). Here we report that the 8000-MW ubiquitin homologue is associated with an intracellular TCR-alpha (but not TCR-beta)-like molecule and released from the cells. The affinity eluates obtained from the culture supernatants of E17 cells and concanavalin A (Con A)-activated splenocytes with anti-TCR-alpha monoclonal antibody (mAb) showed an antigen-non-specific, major histocompatibility complex (MHC)-non-restricted suppression. Immunoblot analysis demonstrated that anti-TCR-alpha, but not anti-TCR-beta, mAb recognizes native 70,000-MW MNSF. In addition, we found the dissociation of the 8000-MW polypeptide from the 62,000-MW TCR-alpha cross-reactive protein by hydrolase which cleaves isopeptide bonds. Thus the covalent attachment of ubiquitin-like protein(s) may be involved in the underlying mechanism of suppressor T-cells and TCR-alpha-like molecule(s) might be a main link between antigen-specific and non-specific suppression.