GEORGES ROELANTS

Two types of functionally different lymphocytes may be distinguished in mice by virtue of their surface antigenic markers (reviewed in reference 1). Thymus-dependent (T) 1 cells do not show immunoglobulin (Ig) detectable by immunofluorescence but bear the 0-isoantigen marker. Thymus-independent (B) cells have easily demonstrable immunoglobulin and lack the 0-marker. The mechanism of interaction between lymphocytes and antigens is not clearly understood. I t is generally accepted that B cells interact with antigen through specific immunoglobulin surface receptors. In experiments where mouse lymphocyte suspensions were exposed in vitro to [125I]antigen of high specific activity, it was found that both T and B cells could be specifically killed by the corresponding antigen, pointing toward specific receptors on T cells as well (2-4). This T cell "suicide" could be prevented by pretreatment of the cells with anti-K chain serum (2), but tile nature of T cell receptors is, however, still highly controversial (reviewed in references 5 7). [I25I]Antigen binding to cells can also be visualized by autoradiography (reviewed in references 7 and 8), and it was found that part of the binding cells could be suppressed by treatment with anti-0 serum and complement and represented thus presumably T cells (9). The same observation was made using immunocytoadherance to detect binding cells (10 12).