Depressed Cellular and Humoral Hemolysin Responses of Rabbits Injected Intraperitoneally with Mineral Oil before Immunization

Abstract Intraperitoneal injection of rabbits with mineral oil 4 days before challenge immunization with sheep erythrocytes, by the same route, resulted in a delay in appearance of antibody and a significant depression of both the serum antibody response and the number of antibody plaque-forming cells. There was a 90% or greater suppression of the number of antibody-forming cells in the spleen and mesenteric lymph nodes of rabbits pretreated with oil as compared to control animals injected with red blood cells only. Injection of oil on the same day as the red cells resulted in a marked increase in the serum titer, as well as a moderate increase in the number of plaque-forming cells in the spleen and lymph nodes. Some of the antibody detected 7 days after immunization was of the 7S class, as indicated by 2-mercaptoethanol resistance. Sera from normal animals and animals pretreated with oil contained mainly 19S hemolysins during the first 2 weeks after immunization. Challenge immunization of rabbits by the intravenous route circumvented the immunosuppression induced by intraperitoneal injection of oil. Rabbits treated with oil either simultaneously or 4 days before intravenous immunization had as good or greater an antibody response than control animals. However, most of the plaque-forming cells appeared in the spleen, with very few in the mesenteric lymph nodes. Four days after oil injection over 90% of the peritoneal exudate were macrophages. The role of such macrophages in the immune response, as well as the nature of the effect of oil on these cells, is discussed in relation to reticuloendothelial system blockade and antibody formation.