Eighteen different strains of were all shown to produce an EDTA-sensitive proteinase of 50 kDa that cleaved the heavy chain, but not the light chain, of IgG. Digestion of pure IgG with small amounts of pure proteinase generated Fabc' and Fab' fragments; greater amounts generated Fab and Fc fragments that were comparable in size to those generated by pepsin and papain, respectively. Incubation of neutrophils with IgG digested with proteinase or papain resulted in a marked decrease in the respiratory burst activity of the neutrophils that coincided with cleavage of the IgG into Fab and Fc fragments. Analysis of urine from patients with urinary tract infection revealed in many the presence of Fab and Fc fragments of IgG indistinguishable in size from those generated by proteinase. These results indicate that, in urinary tract infections, the proteinase is secreted and cleaves IgG to fragments that have defective immune effector functions, thereby limiting the effectiveness of the immune response.


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