Structural differences in cell surface T25 polypeptides from thymocytes and cloned T cells.

The molecule bearing the Thy-1.2 antigen, T25, has been isolated from fractionated thymocytes as well as from cloned cytolytic and helper T cells by immune precipitation with monoclonal antibodies. Using NaDodSO4/polyacrylamide gels cross-linked with N,N'-diallytartardiamide, electrophoretic analyses of the precipitates revealed a heterogeneous pattern of polypeptide bands, ranging in apparent molecular weight from 28,000-36,000 daltons. Thymocytes separated on the basis of Thy-1.2 surface antigen density were found to differ not only in amount of Thy-1.2 expressed, but also in the structure of the surface T25 molecules isolated from each subpopulation. This structural variation was evidenced in changes detected in the relative density and electrophoretic mobility of T25 band patterns obtained on SDS gels. Differences in T25 band patterns were also observed in polypeptides isolated from cloned cytolytic or helper T cells. These data suggest that although surface T25 is structurally heterogeneous, the pattern of heterogeneity can differ from cell to cell, or from population to population. Changes in T25 structure appear to correlated with differences in either T lymphocyte maturation or T cell function.