Experimental humoral and cellular immunity to hog intrinsic factor.

Humoral and cellular immunity to hog intrinsic factor (HIF) was studied in rabbits immunized with varying doses of HIF or HIF complexed to vitamin B. Animals immunized with large doses of HIF (1 mg) consistently produced high titres of blocking and binding antibodies to IF. At low dose immunization (10 μg), the humoral response was obviously blunted, with animals forming significantly reduced titres of antibodies to IF; several rabbits in this group made only binding antibodies and one rabbit produced neither blocking nor binding antibodies. No difference in humoral responsiveness was noted between those animals who received HIF or an equivalent amount of HIF complexed to vitamin B. By contrast, cellular immunity as measured by inhibition of leucocyte migration was readily induced to a similar degree in both high and low dose animals, including the rabbit which had no detectable antibodies to IF. When an intermediate dose of HIF (50 μg) was used as the immunogen, four rabbits gave positive leucocyte migration tests only with HIF—vitamin B complex, suggesting that the interaction of HIF with vitamin B may enhance its antigenicity . These data demonstrate that cellular and humoral immunity to HIF can be induced and partially dissociated from each other by varying the dose of immunogen. Although the mechanism responsible for this dissociation is not clear, one explanation would be differing sensitivities of lymphocyte-populations to different doses of antigen.