An experimental animal model is described in which small injections of antigen (SRBC) into the portal venous system of the rat produces a reduced immune response in comparison with that obtained following similar injection into the inferior vena cava. The difference in humoral response, measured by circulating haemagglutinins and haemolysins was only detectable after repeated doses of antigen. The dose of SRBC necessary to demonstrate this difference is shown to be critical. Cell-mediated immunity—determined by measuring ear swelling 24 hours after intra-auricular injection of antigen—could be demonstrated in animals immunized via the inferior vena cava but not in those immunized via the portal vein.
Labelling of the antigen with radioactive chromium (51Cr) showed that the increased immune response to inferior vena cava injected antigen was accompanied by a reduced hepatic uptake of antigen, but no significant alteration in splenic uptake.