The expression on mouse lymphoid cells of Th-B, an antigen common to mouse B cells and thymus cells.

A new cell-surface antigen of mouse lymphocytes, which was found earlier on normal and malignant plasma cells and about half the normal thymus cell population, has been shown to be on mature B cells and on the least immunocompetent subpopulation of cells of the thymus. The antigen was first detected by the cytotoxic effect on relevant cells of an in vivo purified rabbit antiserum raised against cells of the mouse IgM-producing plasma cell tumor MOPC-104E. We have now used a cell-transfer method to examine the effect of this antiserum (RantiM104E) on immunocompetent lymphocytes of spleen, including separated splenic B and T cells and thymus and bone marrow cells. We have found the antigen on the immunocompetent B lymphocytes of the spleen, but not on any other of the immunocompetent cells examined. The method involves determining the effect of the antiserum on the development of plaque-forming cells in the spleens of irradiated mice that have received lymphocytes from immune or non-immune donors by treating the lymphocyyes with RantiM104E antiserum before transfer. Plaque-forming cells are suppressed when antiserum-treated spleen cells are transferred to the irradiated mice.This suppression was found to be due to action on only the splenic B cells. The helper activity of splenic T cells was not reduced significantly by antiserum treatment. Neither was the helper activity of thymus cells similarly treated reduced by the antiserum. We found, in fact, that the subpopulation of the thymus cells which is resistant to the antiserum was more immunocompetent than the total thymus cell population. In addition, the hydrocortisone-resistant thymus cells were also found to be resistant to the cytotoxic action of the antiserum. The antiserum had no effect on bone marrow cells in the cell-transfer procedure. The antigen involved, which we are designating "Th-B" appears to be a B cell line marker which appears relatively early during the differentiation of mouse B cells from precursor cells and is lost during maturation of T cells.