Cloning of a cDNA for a T cell produced molecule with a putative immune regulatory role.

An expression cDNA library was constructed from the helper T cell hybridoma, A.1.1, which has been shown to produce constitutively proteins involved in the down regulation of the immune response. From this library we identified and characterized a cDNA clone, J6B7, by screening with a polyclonal antibody specific for secreted immune regulatory proteins. The mRNA for J6B7 is expressed specifically in some T cells, but not in the thymoma BW5147 or liver cells. J6B7 is 2937 nucleotides in length and contains one open reading frame encoding for a peptide of predicted Mr of 98,042. The nucleotide and deduced amino acid sequences of J6B7 did not reveal significant homology to any published sequences. Hybridization and translation experiments reveal that the J6B7 can hybrid select mRNA from total RNA isolated from either A.1.1 cells or thymic tissue which can be translated in vitro to a peptide which is bound by a monoclonal antibody (mAb) specific for antigenic determinant(s) shared by immune regulatory proteins. Furthermore, the in vitro translated proteins obtained from A.1.1 cells and thymus showed significant suppression of a mixed lymphocyte reaction (MLR) in a dose dependent manner, reaching maximum suppression of 71% and 89%, respectively. These results suggest that the cDNA, J6B7, codes for an immune regulatory protein.