Affinity of antibody at a secretory site in the rat.

Sprague-Dawley rats were administered DNP-BGG on day one of pregnancy by either local mammary gland vicinity injection or by gastric intubation. All rats later received local mammary gland vicinity injection of DNP-BGG on day 11 of pregnancy. Milk and serum were collected post-parturition. IgA and IgG antibody was separated in the milk and IgG antibody in the serum. The relative average affinity constant (KO) was determined by a modification of the Farr assay. Milk IgG affinity was found to be considerably higher than the affinity of IgG in the serum. IgA affinity in the milk of rats which received the antigen by gastric intubation demonstrated antibody affinity much greater than the affinity of milk antibody in rats which simply received mammary gland vicinity injection (1.8 x 10(8) vs. 1.4 x 10(6) l/M). The results indicate that much of the IgG antibody in milk may be locally synthesized. Gut-associated lymphoid tissue may act as a source of antigen specific memory cells for peripheral secretory tissues.