Human T lymphocyte receptors for sheep red blood cells and specific antigens: are they identical sites on the cell membrane?

The cell surface of human T lymphocytes is characterized by the presence of specific antigens and by E-receptors for sheep red blood cells (SRBC). The exposure of human T cells to specific anti-T sera inhibits the formation of E-rosettes. The relation between E-receptors and specific T cell antigens was investigated in a number of human cell lines and in enzyme-treated lymphocytes. Cells of the Molt-4 line were found to be susceptible to the cytotoxic effect of rabbit anti-human thymus serum (RAHT) rendered specific for human T cells by absorptions. The line of Molt-4 tested failed to form E-rosettes with either untreated or neuraminidase-treated SRBC. Thus, Molt-4 cells seemed to possess T cell-specific antigens in the absence of detectable E-receptors. A second line, K-562, formed E-rosettes with neuraminidase-treated SRBC. Although K-562 cells seemed to possess E-receptors similar to those on PBL, they were resistant to the cytotoxic effect of RAHT, and exposure to RAHT failed to inhibit the formation of E-rosettes by K-562 cells. Trypsin treatment of either PBL or thymus cells totally eliminated their ability to form E-rosettes, but did not significantly alter their susceptibility to the cytotoxic effect of RAHT. Although E-receptors may be located in close proximity to T cell-specific antigens on the membrane of T lymphocytes, the present findings indicate that these two surface markers constitute distinct entities.