Immune response of rabbits to intrarectal injections of particulate and soluble antigens with and without enemas.

New Zealand and New York State Flemish giant rabbits were immunized by intrarectal injections of intact sheep red blood cells (SRC) or sonicated whole sheep blood, with or without prior enemas, and were challenged intravenously with SRC. Animals receiving seven injections of 20% washed SRC, with or without prior enema, did not show detectable humoral response or produce plaque-forming cells (PFC). The systemic humoral response increased moderately after a greater dose of SRC but increased sharply after immunization with sonicated whole blood. These results suggest that particulate antigens have a restricted intestinal absorption, which can be overcome by some degree of degradation or fragmentation. The consequent sensitization to intact and sonicated SRC at the intestinal level was suggested by a secondary type of immune response (IgA and IgG), as shown by the results of PFC counts and the lack or relatively low production of hemagglutinating and hemolysin antibodies. The immune response to both soluble and disrupted particulate antigens was significantly increased by a preceding enema. These animals responded much faster and produced antibodies to a wider range of plasma proteins and SRC stromata. Our findings suggest that frequent enemas may predispose to infection and immunodeficiency in some homosexual males.