Perturbation of mucosal immune defence mechanisms by bacterial IgA proteases.

The secretory IgA system plays an important role in protecting the mucous membranes of the respiratory tract from attacks by microorganisms and potential allergens. We present evidence of in vivo cleavage of S-IgA1 in nasopharyngeal secretions by IgA1 proteases excreted by certain bacteria colonizing the upper respiratory tract. A procedure in two stages, which includes separation of secretion constituents by HPLC and subsequent immunochemical analysis of the fractions by two ELISA systems, identified the S-IgA fragments observed in some nasopharyngeal secretions as intact (FC alpha)2 . SC and Fab alpha, respectively. It is conceivable that colonization of areas of the respiratory tract by increased numbers of IgA1 protease-producing bacteria might cause a local impairment of the mucosal immune barrier. It is hypothesized that such bacterium-induced changes may be a primary event in the pathogenesis of certain inflammatory respiratory diseases and some forms of atopy.