Resting and activation antigens of T cells: studies with OKT10 and OKT20 monoclonal antibodies.

OKT10 and OKT20 are monoclonal antibodies that recognize cell surface antigen(s) on resting thymocytes, plasma cells, null cells, monocytes, and some bone marrow cells. The respective antigens, poorly expressed on resting peripheral T cells, are strongly expressed on T cells activated either in vitro or in vivo. Double-staining experiments using either OKT10 or OKT20, in combination with OKT3, provided paradoxical results. If indirect staining with OKT3 plus horse alpha-mouse IgG preceded staining with OKT10 or OKT20, most cells showed double staining; all other staining sequences yielded the expected result that OKT3+ cells expressed very little OKT10 or OKT20. Analysis of the experiments revealed that perturbation of the cell membrane with a monoclonal antibody reactive with a cell surface antigen (for example, OKT3) followed by a crosslinking second antibody caused the expression of these antigens. This suggests that these antigens, normally expressed on activated T cells, are actually present in an unexpressed form within the membrane of resting T cells.