Mitogenic response of human peripheral blood lymphocytes to a purified C. albicans polysaccharide fraction: lack of helper activities is responsible for the in vitro unresponsiveness to a second antigenic challenge.

Human peripheral blood lymphocytes primed with MPPS (a polysaccharide fraction extracted from C. albicans) were unable to respond to a second challenge of the same antigen. The proliferative response of these lymphocytes was restored by both mitomycin C-treated fresh autologous lymphocytes and by helper factors. Removal of Ia+ cells from fresh lymphocytes abolished the helper effect. On the other hand, when primed lymphocytes were depleted of Ia+ cells, the helper factor-responding cells were eliminated, whereas Ia- cells maintained the capacity to respond to fresh autologous lymphocytes. A model for cell-cell cooperation involved in the regulation of the immune response to this antigen is proposed.