Survival of Miamiensis avidus (Ciliophora: Scuticociliatia) from antibody-dependent complement killing

Previously, we had reported that some Miamiensis avidus, a major pathogen of scuticociliatosis in cultured olive flounder, strongly agglutinated by flounder immune sera could escape from the agglutinated mass within a few hours. In the present study, we observed that M. avidus not only escaped from the agglutinated mass but also conducted division(s) before shedding its old covering. Furthermore, ciliates that survived the antibody-dependent complement killing (ADCK) assay were not killed even when re-exposed to a freshly prepared ADCK assay. This result suggests that the liberated ciliates from the ADCK assay might change not only their i-antigen types but also the epitopes of major surface antigens, which debilitate antibody-mediated complement killing ability.