Flush exposure and injection immunization of rainbow trout to selected DNP conjugates

Rainbow trout (Salmo gairdneri) were immunized by flush exposure or intraperitoneal injection with single doses of the following dinitrophenyl (DNP) conjugates: DNP-keyhole limpet hemocyanin (KLH), DNP-Ficoll, DNP-O-antigen (from the fish pathogen, Yersinia ruckeri), DNP-sheep red blood cells, or DNP-duck red blood cells. The immune response was demonstrated by the passive hemolytic plaque assay to show splenic antibody-producing cells (APC) 14 days after antigen administration. High numbers of splenic APC specific for the hapten were found when the conjugates DNP-KLH, DNP-Ficoll, and DNP-O-antigen were given by injection and when DNP-O-antigen was given by flush exposure. The heterologous red blood cells were relatively nonimmunogenic. When the immune response to the hapten and carrier could be measured--e.g., after immunization with the DNP-O-antigen--the numbers of APC were consistently higher for the hapten.