Antibody binding following exposure of live Ichthyophthirius multifiliis (Ciliophora) to serum from immune carp Cyprinus carpio

Trophont stages of the c~l ia te fish parasite Ichthyophtl~jrius n~ult i f i l i is were Incubated alive in vitro in serum from immune carp Cyprinus carpi0 and subsequently examined immunoh~stoloyically for bound ant~body. Parasites became immobilized in immune serum and were enveloped by gelatinous mucus-llke material. Carp antibody could not be detected bound to cilia membranes (the major surface antigens), although it was detected at low levels in parasite food vacuoles and associated with the gelatinous material. This material is probably responsible for the immobilization of parasites, and may form a barrier that prevents access of large amounts of ci l ia-membrane-spec~f~c antlbody to the parasite surface during in vitro incubat~on In f ~ s h serum.