Antibacterial Action of Specific IgA and Transport of IgM, IgA, and IgG from Serum into the Small Intestine

The antibacterial effects of the various classes of antibodies specific for Escherichia coli were studied by isolation and purification of the three main classes of immunoglobulins from both porcine and lapine colostrum. The purified proteins were examined for their ability to promote phagocytosis and intracellular killing by the peritoneal cells of normal mice. Of the three immunoglobulins, the specific IgA had more activity against E. coli than either IgM or IgG. The transport of 131I-Iabeled antibodies from serum into ligated intestinal loops of the rabbit was investigated; it was found that IgG, and, to a lesser extent, IgA and IgM were transported into the gut. The results suggest that the IgA that is secreted by intestinal cells does have an important role in intestinal immunity.