ANTIBODY-MEDIATED EFFECTS ON PARASITE BEHAVIOR - EVIDENCE OF A NOVEL MECHANISM OF IMMUNITY AGAINST A PARASITIC PROTIST

The parasitic ciliate Ichthyophthirius multifiliis is well known in co mmercial aquaculture ns thp etiological agent of 'white spot', a disea se that afflicts a wide range of fresh-water Fsh. While Ichthyophthiri us is highly pathogenic, animals exposed to controlled infections deve lop a strong acquired resistance to the parasite. Recent studies sugge st host resistance involves a novel mechanism of humoral immunity affe cting parasite behavior. Rather than being killed, parasites are force d to exit fish prematurely in response to antibody binning. The target antigens involved in this process a re a class of high ly abundant gl ycosylphosphatidylinositol-anchored coat proteins referred to as immob ilization antigens, or i-antigens. Here, Theodore Clark and Harry Dick erson describe this phenomenon and offer a number of hypotheses that c ould account for the forced exit.