Non-MHC-restricted T cell antigen-binding proteins

Extracellular (soluble) antigen-specific T cell proteins related to the T cell receptor for antigen (sTCRr): serologic and primary amino acid sequence similarity to T cell receptor alpha chains and association with cytokines

Antigen-specific-effected immunoregulation by T lymphocytes is mediated by extracellular proteins produced by T lymphocytes. These immunoproteins bind specifically to nonprocessed antigen and either induce antigen-specific immunoregulatory T cells (tsfi) or effect regulation (tsfe). T cell proteins that bind specifically to nonprocessed antigen have ben termed "T cell antigen-binding molecules" (TABM), and by definition, tsfe and tsfi are, in part, TABM. To characterize tsfi, tsfe, and TABM and understand the relationships and function of these immunoproteins, we have combined the efforts of two laboratories to compare tsfi, tsfe, and TABM isolated by each laboratory. Data obtained in one laboratory were reproduced by the other, and all reagents prepared by each laboratory were exchanged. TABM, tsfi, and tsfe were found to express TCRCalpha epitopes but not TCRCbeta epitopes. The amino acid sequence of a tryptic peptide of a T cell hybridoma TABM specific for nitrophenylhydroxy acetate (NP) is similar to a TCRalpha chain and TCR pre-alpha chain amino acid sequence. ELISA and immunoblotting demonstrated that Mr 77,000 T cell hybrid-derived tsfi, tsfe, and TABM are noncovalently associated with Mr 15,000-16,000 interleukin-10 (IL-10). ELISA also demonstrated that tsfi and tsfe are associated with I-J. The ability of tsfi and tsfe to suppress a mixed lymphocyte reaction was prevented by anti-IL-10 or anti-I-J antibodies, suggesting that antigen-specific immunoregulatory T cell proteins function by an antigen-specific focusing of immunoregulatory cytokines.

Partial amino acid sequence of monoclonal extracellular antigen-specific T cell proteins

Antigen-specific molecules secreted by murine T cell hybrids (TABM) specific for 4-hydroxy 3-nitrophenyl (NP) or azobenzenearsonate (ABA) were purified from ascitic fluid by ion exchange chromatography and/or affinity for antigen. Partial amino acid sequence of reduced Mr 72,000 NP-specific polypeptides and Mr 20,000 peptides prepared by treatment of the ABA-specific immunoprotein with cyanogen bromide was obtained and a septapeptide of the NP-specific TABM shared 3/7 residues with the ABA-specific TABM. Both TABM shared residues present in 95% T cell receptor for antigen (TCR) V alpha subgroup I and 83-96% murine immunoglobulin V kappa Fr3. These results provide evidence that extracellular antigen-specific T cell proteins are soluble analogues of TCR alpha chains and belong to the immunoglobulin supergene family.