Cells involved in the in vitro stimulation by DNP-carrier complexes of in vivo primed mouse spleen cells.

The target cell of stimulation of primed spleen cells by hapten—carrier complexes was studied. The antigens DNP—bovine serum albumin (DNP—BSA), which gives only 2,4-dinitrophenyl (DNP) specific responses and DNP—mouse immunoglobulin (DNP—MIg), which probably reveals DNP as well as carrier specificity (new antigenic determinant) were used. Educated T cells could be stimulated with the antigens used for activation. A similar experiment with educated B cells, however, gave no indication that these B cells could be stimulated with antigen in the absence of T cells. Cortisone treatment of primed mice yielded spleen cells which had a higher activity than spleen cells from unprimed, cortisone-treated mice. This also points to stimulation of T cells by antigen. Treatment of primed spleen cells with anti-thymocyte serum (ATS) and complement (C) abolished stimulation by phytohaemagglutinin (PHA) completely, by lipopolysaccharide (LPS) slightly, while the antigen-specific activity was 90 per cent reduced. This indicates a mainly T cell-specific stimulation by the antigen. A corresponding experiment with anti-plasma cell serum (APCS) and C revealed a complete reduction of LPS activity and a small impairment of the PHA and conavalin A (Con A) activity. However, the antigen-specific activity was reduced by one-third to a half for the different antigens. This is an indication for a specific B-cell stimulation by the antigen, although it is on a lower level than the T-cell stimulation. The role of the hapten in the T-cell stimulation is discussed.