The thymic differentiation markers T6 and M241 are two unusual MHC class I antigens.

The human beta 2-microglobulin (beta-2m)-associated human thymocyte differentiation antigens T6 and M241 were compared using biochemical techniques. T6 and M241 antigens reside on different molecules with apparent m.w. of 49,000 and 43,000, respectively. Here we show that both proteins have a protein backbone m.w. of 33,000. In addition, T6 and M241 have a large portion of their peptides in common. When we compared the protein backbone m.w. of T6 and M241 with the murine beta-2m-associated thymus leukemia (TL) antigens, we found a considerable difference in size, suggesting that T6 and M241 may not be human homologues of TL antigens and constitute a novel type of major histocompatibility (MHC) class I antigens.