ANTIBODIES TO INTESTINAL MICROVILLOUS MEMBRANES

Abstract

Microvillous membranes isolated from the distal, but not proximal, half of hamster small bowel induced in rabbits the formation of antisera which inhibited intrinsic factor-mediated uptake of vitamin B12 by hamster brush borders. The extent of inhibition was directly proportional to the concentration of antiserum, and an excess of IF-bound vitamin B12 could overcome the inhibitory effect. The inhibitory factor was absorbed from antisera by brush borders isolated from the distal, but not proximal, half of the hamster intestine. Fractionation of antisera by gel filtration and DEAE-cellulose chromatography established that immunoglobulin G contained the inhibitory factor. Antisera capable of completely blocking uptake of IF-bound vitamin B12 did not react with hamster IF or with the IF-vitamin B12 complex, did not inhibit brush border disaccharidase activity and did not impair glucose transport by everted sacs of hamster intestine. These results demonstrate that an antibody to distal microvillous membranes competes with the IF-vitamin B12 complex for a specific binding site or receptor located on the surface of distal hamster intestine.