Secretory leukocyte protease inhibitor binds to Neisseria gonorrhoeae outer membrane opacity protein and is bactericidal.

PROBLEM: Secretory leukocyte protease inhibitor (SLPI) is an innate immune peptide present on the genitourinary tract mucosa that has antimicrobial activity. In this study, we investigated the interaction of SLPI with Neisseria gonorrhoeae. METHOD OF STUDY: ELISA and far-Western blots were used to analyze binding of SLPI to gonococci. The binding site for SLPI was identified by tryptic digests and mass spectrometry. Antimicrobial activity of SLPI for gonococci was determined using bactericidal assays. SLPI protein levels in cell supernatants were measured by ELISA, and SLPI mRNA levels were assessed by quantitative RT-PCR.
RESULTS: SLPI bound directly to the gonococcal Opa protein and was bactericidal. Epithelial cells from the reproductive tract constitutively expressed SLPI at different levels. Gonococcal infection of cells did not affect SLPI expression.
CONCLUSION: We conclude that SLPI is bactericidal for gonococci and is expressed by reproductive tract epithelial cells and thus is likely to play a role in the pathogenesis of gonococcal infection.