Suppressive effect of a chronic helminth infection, schistosomiasis mansoni, on the in vitro responses of spleen and lymph node cells to the T cell mitogens phytohemagglutinin and concanavalin A.

Chronic murine schistosomiasis mansoni is associated with depressed cell-mediated immune responses to Schistosoma mansoni egg antigens. The present study has examined the possibility that factors develop during infection that are capable of altering the response of lymphocytes to stimuli other than specific schistosomal antigens. Egg production begins at 5 weeks, and 1 to 3 weeks later there is a moderate degree of unresponsiveness of lymph node and spleen cells to the mitogens concanavalin A and phytohemagglutinin. This was associated with an altered dose response curve to the mitogens similar to that observed in antigenic systems. Seven weeks after the initiation of antigenic stimulation (egg prodiction lymph node and spleen cells from chronically infected animals were profoundly unresponsive to all concentrations of concanavalin A and phytohemagglutinin tested. These investigations suggest that, in addition to possible blockade by serum antibody, other suppressive factors may be involved in the spontaneous modulation of immunopathology in chronic schistosomiasis. These are detectable 1 to 3 weeks after the onset of egg production and are prominent at 12 weeks. Such findings are consistent with, but do not prove, the existence of suppressor T cells in chronic schistosomiasis.