Distribution of alpha-chain subclasses in normal and pathological IgA-globulins.

Of 332 monoclonal IgA-components, 6·6 per cent belonged to the subclass, and the remainder to the subclass of α-chains. The light-chain type distribution (κ or λ) was not statistically different in these two subclasses, being 54·5 and 57·7 per cent, respectively. Proteins of subclass tended to occur at higher average concentrations in the pathological sera, and were of a higher electrophoretic mobility, than were components of the type. From a comparison of the concentrations of -type IgA and total IgA (+) in a large number of individual sera without monoclonal components, it was concluded that the proportions of -type and -type molecules were approximately the same (i.e. 93·4:6·6) in most individuals. The data suggest that - and -type IgA molecules are produced by separate gene loci.