IgA half molecules. II. Genetic variants of IgA detected in normal mouse intestinal contents.

Six two chain IgA myeloma proteins are found to have very similar molecular weights and to share immunochemical characteristics suggesting that they represent examples of an unusually small-sized variant of normal mouse IgA. With the use of homologous antiserums in 2-dimensional double diffusion and hemagglutination inhibition, small amounts of this unusual IgA were detected in normal BALB/c intestinal contents. Gel filtration of the intestinal contents suggests that these gut immunoglobulins A exist in a size consistent with a single light chain plus a single heavy chain and can be regarded as IgA "half molecules" or IgAb. We feel that IgAb represents a normal variant of mouse IgA, but the possibility of its being a second mouse IgG subclass is discussed.