Origin and molecular size of immunoglobulin-A in the mesenteric lymph of the dog

Abstract

Samples of mesenteric lymph, thoracic duct lymph or lymph of mixed (hepatic and intestinal) origin from adult dogs were compared with serum from the same animals with regard to the concentrations of different proteins, particularly IgA, IgM, IgG₁, IgG_2ab and IgG_2c. In all samples the lymph to serum ratio for IgA was found considerably to exceed the corresponding ratios for the other immunoglobulins. From these data it was calculated that from 60 per cent to over 95 per cent of the IgA in mesenteric lymph was produced by the plasma cells of the intestinal mucosa, and that the latter significantly contributed to the pool of circulating IgA.

The molecular size of IgA from canine mesenteric lymph was found to be indistinguishable from that of canine serum IgA, as judged by ultracentrifugation in a sucrose density gradient. Both forms of IgA were significantly heavier than human 7S IgG, and sedimented almost as fast as 11S IgA from human milk. It was concluded that canine serum IgA predominantly exists in the form of a dimer.