Inhibition of in vitro lymphocyte proliferation by brain glycoprotein (NSA3) and mesenchyme-associated antigen (MAA)

Summary Two cross-reacting antigens, one (NSA₃) associated with nervous system and the other (MAA) present in mesenchyme and different types of tumors, were shown to inhibit the mitogenic effect of PHA, Con-A, and PPD on normal peripheral human lymphocytes. They do not affect the response to allogeneic cells in the one-way mixed lymphocyte reaction. The two antigens also suppress in vitro response to PPD obtained with lymphocytes isolated from BCG-treated patients. The lack of effect on unstimulated lymphocytes and on MLR allows the exclusion of cytotoxic action by our antigen preparations. These data, taken in conjunction with previously obtained results concerning inhibition of E active rosette formation, give rise to the hypothesis of an antigen action directed against a T cell subpopulation. These results also suggest that MAA, in association with other tissue and tumor factors, could play a role in tumor-induced immunosuppression.