Down-regulation of murine lymphocyte responsiveness to mitogens after treatment with antigens of Entamoeba histolytica.

Injection of mice with pathogenic Entamoeba histolytica (strain HM1-IMSS) antigens resulted in a decreased capacity of splenocytes to respond to mitogen-induced blastogenesis following a challenge with concanavalin A (Con A), phytohemagglutinin (PHA), and lipopolysaccharide (LPS), whereas no inhibition was observed in mice that had previously been injected with equivalent amounts of non-pathogenic E. histolytica-like Laredo antigens. Depletion of adherent cells in the splenocyte preparation indicated that these cells were not a major contributor to the observed immunosuppression. Quantification of splenic T-lymphocyte subsets demonstrated a significant decrease in Thy-1+ and Lyt-1+ cells, but Lyt-2+ cells were not affected. Splenocytes treated with pathogenic amoebic antigens in vitro affected the capacity of these cells to respond optimally to Con A- and LPS-induced blastogenesis but not to that induced by PHA. These findings demonstrate that amoebic antigens affect lymphocyte function and may be important co-factors in the immunoregulation and pathogenesis of amoebiasis.