How Schistosoma mansoni evades complement-mediated immune attack

RESUMO

Schistosoma mansoni is a trematode that parasitizes man and other mammals, surviving in the vertebrate host for decades, despite eliciting a strong cellular and humoral immune response. The mechanism by which S. mansoni evades immune attack, even in the presence of specific antischistosome antibodies and complement has been the object of perplexity. It was originally proposed that schistosomes avoid antibody recognition by masking themselves with host antigens, and erythrocyte-derived molecules have been appointed as playing this role. We have discovered that schistosomula become complement-resistant by incorporating into their surface a complement inhibitory molecule released from human erythrocytes (HuE). This molecule was shown to be the decay-accelerating factor (DAF), a 70 kDa protein tethered to the surface of HuE by a glycosylphosphatidylinositol (GPI) anchor. The mechanism by which schistosomula acquire DAF from the surface of HuE and its importance to the survival of S.mansoni in the host are discussed.