IS TUMOR-NECROSIS-FACTOR-ALPHA THE MOLECULAR-BASIS OF CONCOMITANT IMMUNITY IN SCHISTOSOMIASIS

Prior to the development of high levels of resistance to infection wit h schistosomes, some mechanism appears to limit the number of producti ve worms in individuals, since children do not become superinfected, d espite continued exposure to infection. One way in which infection lev els might be limited, is through the generation of a concomitant immun ity. Concomitant immunity results in the destruction of newly invading schistosomula whilst established adult worms continue to survive. Rec ent studies have provided evidence that TNFalpha enhances worm fecundi ty and is essential for granuloma formation. TNFalpha may therefore be important in worm reproduction and transmission, since the granuloma may serve to assist the passage of the eggs out of the tissues. With t he additional evidence that the cytotoxic activity of lymphokine-activ ated macrophages against schistosomula may be, at least in part, due t o the action of TNFalpha, we propose that TNFalpha may also be respons ible for the phenomenon of concomitant immunity.