Antigen competition: antigens compete for a cell occurring with limited frequency.

Experimentally altered ability of transferred spleen cells to generate hemolytic plaque-forming cells provided evidence that antigens compete for a type of multipotential cell that contributes to the formation of immunologically competent units. De'ay of exposure of transferred spleen cells to antigen provided results which suggest that different types of cells interact to form competent, antigen-reactive units even in the absence of antigen.