Granulomatous hypersensitivity to Schistosoma mansoni egg antigens in human schistosomiasis. III. In vitro granuloma modulation induced by immune complexes.

Granulomatous hypersensitivity to parasite eggs of Schistosoma mansoni is an important factor in the development of morbidity in chronic schistosomiasis. It has been demonstrated previously that the chronic, well-tolerated, intestinal form of schistosomiasis is associated with the establishment and maintenance of a variety of immunoregulatory mechanisms. We have used an in vitro model of granuloma formation for the purpose of studying the regulation of granulomatous hypersensitivity to S. mansoni egg antigens, mediated by immune complexes (IC). Our results show that the peripheral blood mononuclear cells (PBMCs) from patients with active schistosome infections, when treated with sera from chronic schistosomiasis patients, were able to induce an inhibitory activity on in vitro granuloma formation. Significant modulation of the in vitro granuloma reaction remained after treatment of PBMCs with isolated IC or manufactured IC with soluble egg antigen (SEA) and purified IgG from pooled chronic schistosomiasis sera. In contrast to granuloma modulation stimulated with whole molecule IgG-SEA IC, the incubation of PBMCs with F(ab')2 IgG-SEA IC did not induce any suppression of the granulomatous hypersensitivity to SEA. It appears in this model system that IC may inhibit the activity of granuloma formation by stimulating macrophages to release suppressive mediators. We have demonstrated this possibility by inhibition of prostaglandin activity using indomethacin. The addition of indomethacin to the granuloma culture significantly reduced in vitro granulomatous hypersensitivity to S. mansoni eggs in patients with chronic intestinal schistosomiasis and do so by inducing macrophages to secrete prostaglandins.