IgA1 protease production by bacteria colonizing the upper respiratory tract

Thirty-eight clinical isolates of Haemophilus influenzae and ten clinical isolates of Streptococcus pneumoniae were examined for IgA1 protease production. A suspension of surface material of each individual strain was incubated with human secretory IgA; IgA1 cleavage products were detected by SDS-PAGE and immunoblotting. The high incidence of IgA1 protease-positive strains (68.4% of the examined H. influenzae and 100% of the examined S. pneumoniae strains) confirms that IgA1 protease activity is a frequent characteristic of these two species. Yet the presence of this enzyme is, if at all, only a minor decisive factor for the induction of symptomatic infections of the upper respiratory tract by IgA1 protease-positive bacteria.