IMMUNOREGULATORY ACTIVITY OF A T-CELL RECEPTOR-ALPHA CHAIN DEMONSTRATED BY IN-VITRO TRANSCRIPTION AND TRANSLATION

Previous studies from our laboratory and those of others suggested the possibility that the T-cell antigen receptor alpha (TCR alpha) chain from some T cells can be released in a soluble form and can have antig en-specific immunoregulatory activity, We have analyzed this phenomeno n by in vitro transcription and translation (IVTT) of a cDNA encoding a TCR alpha chain (A1.1 TCR alpha) suspected of having such activity, We found that TCR alpha, but not TCR beta, protein produced in this wa y showed antigen-specific regulatory activity in an in vitro immune-re sponse assay, Protein derived from truncated forms of the A1.1 TCR alp ha cDNA had activity providing that, in addition to the variable (V) a nd Joining (J) regions of the alpha chain (VJ alpha), at least the fir st 25 amino acids of the alpha chain of the constant (C) region (C alp ha) were present. Addition of an irrelevant protein sequence to the VJ alpha failed to impart activity to the molecule, suggesting that the C alpha requirement is not simply for stabilization of the resulting p rotein, These results are discussed in the context of other recent stu dies on the immunoregulatory activity of soluble TCR alpha molecules, and the possible physiological relevance of these observations is cons idered.