Differential expression of RT1 class II genes in fibroblast cell lines: recognition by allogeneic and xenogeneic T lymphocytes.

A cosmid (cos a 13.1) containing RT1 class II B alpha and B beta genes was introduced into mouse and rat fibroblast cell lines by transformation. Mouse L cells transformed with cos a 13.1-synthesized cell surface class II molecules that were similar, with respect to apparent molecular weight and binding of xenogeneic- and allogeneic-specific antibodies, to class II molecules on rat B cells. RT1 class II molecules on the surface of mouse L cells were recognized by both allogeneic and xenogeneic T cells. In contrast, rat-2 cells transformed with cos a 13.1 did not synthesize any detectable RT1 class II molecules at the cell surface, and the levels of B alpha and B beta mRNA were generally very low or undetectable. This differential expression of exogenous class II genes was not exclusively due to a trans-acting positive regulatory factor in L cells. Other possible explanations for this difference are discussed.