Characterization of the alloactivated E+Ia+ cell capable of stimulating in mixed lymphocyte culture.

Human peripheral blood E+ lymphocytes were alloactivated by E- cells and then purified by repeat E+ selection. As described by others, alloactivated cells (E+d6) but not unactivated E+ cells were capable of stimulating both allogeneic and autologous mixed lymphocyte cultures (MLC). To further characterize the subset of cells responsible for this function, we used a variety of monoclonal antibodies to human T cells and monocytes. Treatment of E+d6 cells with anti-Ia OKI1) plus complement (C) abrogated their stimulating capacity. In contrast, treatment with the anti-T cell antibodies OKT3, OKT11A, OKT4, OKT8 plus C or anti-macrophage antibody (OKM1) plus C failed to eliminate their MLC stimulatory capacintibodies to human T cells and monocytes. Treatment of E+d6 cells with anti-Ia OKI1) plus complement (C) abrogated their stimulating capacity. In contrast, treatment with the anti-T cell antibodies OKT3, OKT11A, OKT4, OKT8 plus C or anti-macrophage antibody (OKM1) plus C failed to eliminate their MLC stimulatory capacintibodies to human T cells and monocytes. Treatment of E+d6 cells with anti-Ia OKI1) plus complement (C) abrogated their stimulating capacity. In contrast, treatment with the anti-T cell antibodies OKT3, OKT11A, OKT4, OKT8 plus C or anti-macrophage antibody (OKM1) plus C failed to eliminate their MLC stimulatory capacity. Because OKT3 recognizes the majority of T cells and OKT11A recognizes virtually all E+ cells, we reasoned that a contaminating non-T cell containing the MLC-stimulating capacity may be present within the alloactivated E+ population. To further address this question, E+d6 cells were positively and negatively selected using a rosetting technique with anti-Ig-coated red cells. The positively selected OKT3, OKT11A, OKT4, or OKT8 E+d6 cells retained minimal ability to stimulate MLC, whereas the corresponding negatively selected populations were highly enriched in this function. Phenotypic analysis of the isolated populations failed to demonstrate greater than 1% surface membrane Ig(SmIg) positive cells. Taken together, these results suggest that the MLC stimulatory capacity of alloactivated E+ cells is contained within an Ia+, OKM1-, SmIg- non-T cell subset.