Degradation of human immunoglobulins by proteases from Streptococcus pneumoniae obtained from various human sources.

The ability of Streptococcus pneumoniae to degrade human secretory immunoglobulin A (S-IgA), IgG, and IgM was tested in 102 strains by use of the thin-layer enzyme assay cultivation technique. The strains were isolated from patients with acute phases of otitis media, meningitis, and pneumonia as well as from symptomless carriers. An ability to degrade S-IgA, IgG, and IgM was revealed in 50, 84, and 96 strains, respectively. An IgG- and IgM-degrading ability of S. pneumoniae has not previously been reported. A concurrent degradation of the three immunoglobulins was revealed in 38 strains; degradation of two of them was revealed in 54 strains, and degradation of only one of them was revealed in 9 strains. One strain failed to degrade any of the immunoglobulins. Correlations were not found between the ability of the S. pneumoniae strains to degrade S-IgA, IgG, or IgM and the serotype affiliation or between the ability to degrade IgG or IgM and the origin of strains. However, the ability to degrade S-IgA was evident more often in strains isolated from symptomless carriers and from bronchial secretions of patients with acute pneumonia than it was in strains from patients with acute meningitis or acute otitis media or from the blood of patients with acute pneumonia. These latter findings may indicate a biological significance of S-IgA-degrading ability in bacterial colonization of mucosal surfaces.