An antibody forming cell assay is more sensitive than serology for detecting antibody in fish

Fish often fail to make detectable serum antibody after infection by virus. The object of this work was to develop an antibody forming cell assay to determine if such seronegative fish were making antibody. Inactivated Newcastle disease virus was used as the model antigen in 26 fish, 12 koi carp (Cyprinus carpioL.×Carassius carpioL.) and 14 common goldfish (Carassius auratusL.). Using the same immunoperoxidase detection systems for the assay of serum antibody and antibody forming cells in their mesonephros, four of the 26 fish produced serum antibody compared to 22 of the 26 fish producing antibody forming cells. Fish therefore make antibody more frequently than is determined by serology.