Studies on rabbit secretory and serum antibodies to hog intrinsic factor.

The response of the systemic and secretory immune systems to hog intrinsic factor (IF) was studied in rabbits. Following immunization, pregnant rabbits produced both serum and colostral antibodies to IF. Blocking and binding antibodies to IF were consistently found in sera. The colostrum of the four animals studied also contained blocking antibodies, but colostral-binding antibodies to IF were detected in only two rabbits. Blocking antibody in serum was restricted to the IgG fraction, whereas this activity was present in both the IgG and secretory IgA immunoglobulins of colostrum. Binding antibody to IF was also found within the IgG and secretory IgA of colostrum; in serum, however, the binding activity was seen in all three immunoglobulin classes. These data indicate that the systemic and secretory immune systems of the rabbit recognize the two major antigenic sites on IF and produce specific antibodies against these determinants.