A monoclonal antigen-binding T cell immunoprotein: antigenic relatedness to T cell receptor beta chain FR1 V and J peptide segments: physicochemical distinctiveness from classical immunoglobulins and T cell receptor heterodimers.

The monoclonal murine T cell hybridoma, 51H7D, was previously shown to bind the arsazobenzene hapten and to produce a soluble antigen-binding molecule. In this paper we characterize this antigen-binding immunoprotein for its relationship to known T cell receptors serologically, using antibodies specific for variable region framework, or joining region peptides predicted from gene sequence and by biochemical means. The 51H7D cell expresses a protein with subunit size of approximately 31,000, that reacts antigenically with affinity-purified antibodies directed against synthetic first framework and joining segment peptides, corresponding to the gene sequence of the T cell receptor beta chain, YT35. This molecule does not react with affinity-purified antibodies directed against murine immunoglobulin, framework 1 sequences of alpha and gamma T cell receptors, or with antibodies against synthetic heavy chain joining segments. The subunit of mol. wt. 31,000 can form higher aggregates, notably in the mol. wt range of 60,000-70,000, depending upon extraction conditions. The soluble form of the antigen-binding molecule bears the J beta cross-reactive determinant and occurs predominantly as a charge restricted molecular species of approximate mol. wt 60,000-70,000. The purified molecule has a blocked N-terminus, but quantitative statistical analysis of its amino acid composition indicates a closer relatedness to T cell receptor beta chains and other antigen-binding T cell products, than it has to alpha, gamma or delta TCR chains. No evidence for more than one type of polypeptide chain was found and the polymerization is not dependent upon the formation of disulfide bonds. These studies raise the possibility that antigen-binding soluble T cell molecules might belong to a new family of immunoproteins, that is related to, but distinct from, classical immunoglobulins and alpha beta or gamma delta heterodimers.