CD2 enhances the proliferative response of CD4⁻CD8⁺ thymocytes and lymph node cells from H-2^b H-Y mice to stimulation by the male antigen. An equivalent number of CD4⁻CD8⁺ thymocytes or lymph node cells from the indicated mice were cultured with male or female C57BL/6 (B6) spleen cells with or without added IL-2. The proliferative response was determined by assessing thymidine incorporation during the last 16 hours of an 84-hour culture period.