Immunoglobulin A1 protease production by Haemophilus influenzae and Streptococcus pneumoniae

Abstract

Bacterial strains of Haemophilus species and Streptococcus pneumoniae were examined for synthesis of the enzyme immunoglobulin A1 (IgA1) protease. Of 36 H. influenzae strains examined, 35 produced IgA1 protease; strains included all six capsular types, unencapsulated variants of types b and d, and untypable H. influenzae. Eight Haemophilus strains (non-H. influenzae) were studied, and two produced IgA1 protease. All 10 strains of S. pneumoniae produced IgA1 protease; these strains included 9 different capsular polysaccharide types and 1 untypable strain. Both IgA1 proteases cleaved myeloma IgA1 and secretory IgA but not myeloma IgA2, IgM, or IgG as determined by immunoelectrophoresis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that both enzymes cleaved IgA1 myeloma sera, but not IgA2, into two fragments. The apparent molecular weight of the cleaved fragments was dependent both on the apparent molecular weight of the cleaved fragments was dependent both on the specific IgA1 protease assayed and the specific IgA1 substrate utilized. It is postulated that both carbohydrate variation between the IgA1 substrates studied and the ability of S. pneumoniae glycosidases to cleave carbohydrates from glycoprotein offer an explanation for the different fragment sizes observed.