48 Histocompatibility Antigens on Schistosomula

Schistosomiasis is an excellent example of the evasion of the immune response by a parasite. The trematode worms responsible for this disease can survive for many years inside the blood vessels of vertebrate hosts and are apparently undisturbed by the potent humoral and cell-mediated responses which they have been shown to induce. Several mechanisms have been postulated to explain the survival of schistosomes in their immunologically hostile environment. Of these hypothetical mechanisms, perhaps the most intriguing is that proposed by Smithers et al. (1). These workers argue that the schistosome may protect itself against immune attack by coating its surface with molecules of host origin. Their hypothesis is based on the observation that worms living in a given host express on their surfaces species specific antigens characteristic of that host. That the acquisition of these determinants may protect the parasite against immune rejection was suggested by further experiments in which it was shown, that as larval schistosomes (schistosomula) acquire host molecules, they lose the capacity to bind antibodies directed against their own surface antigens (2, 3). The phenomenon of host antigen acquisition by schistosemes has stimulated a number of investigations on the chemical nature of the molecules adsorbed by the worms from the host environment. These studies have suggested that the parasite acquires host material principally in the form of glycolipids. Thus, when cultured together with human erythrocytes of known blood groups, schistosomula acquire A, B, H, and Lewis glycolipid antigens but fail to adsorb other antigens known to exist as glycoproteins (4). Similarly, worms recovered from mice or cultured in the presence of mouse tissue have been shown to express determinants reactive with anti-Forssman antibodies (5).The Forssman antigens have also been characterized as glycolipid molecules. In the present study, we have used a somewhat different approach to investigate the chemical nature of schistosome acquired host molecules. We have asked whether schistosomula recovered from the lungs of mice belonging to genetically defined inbred strains can be shown to express murine alloantigens. An unexpected finding of this study is that among the host molecules