An ELISA method to measure total and specific human secretory IgA subclasses based on selective degradation by IgA1-protease

We have taken advantage of the property of IgA1-proteases to selectively cl eave the human IgA1 subclass into Fab alpha and Fc alpha-J chain-secretory component (Fc alpha-J-SC) fragments in order to design a novel ELISA method for measuring the two secretory IgA (S-IgA) subclasses in secretions. The assay is based on the loss of detection of S-IgA1 by a combination of perox idase-labelled antibodies to secretory component and Fab following IgA1-pro tease treatment. The specificity is that of the protease and the sensitivit y of the detection is 5 ng/ml. Moreover, the use of purified S-IgA1 and S-I gA2 controls is not necessary. The assay has been successfully applied to t he analysis of colostral S-IgA antibodies (Abs) to HIV-1-gp160 from HIV-1 p ositive women. The major subclass of colostral S-IgA antibodies to gp160 wa s found to be of the alpha 1 isotype but the specific activity of anti-HIV- gp160 S-IgA2 was, however, higher than that of S-IgA1. (C) 2000 Elsevier Sc ience B.V. All rights reserved.