Background: Secretory leukocyte protease inhibitor (SLPI) is responsible for regulating inflammatory damage to and innate and adaptive immune responses in the vaginal mucosa. Depressed cervicovaginal SLPI levels have been correlated with both Trichomonas vaginalis infection and poor reproductive health outcomes.
Methods: We measured levels of SLPI in 215 vaginal specimens collected from adolescent and young adult females aged 14-22 years. Log-transformed SLPI values were compared by analysis of variance or by an unpaired t test before and after adjustment for confounding effects through the propensity score method.
Results: Females receiving hormonal contraceptives and those with an abnormal vaginal pH had lower SLPI levels as compared to their peers. After propensity score adjustment for race, behavioral factors, hormonal use, and other sexually transmitted infections (STIs), SLPI levels were lower in females with a positive T. vaginalis antigen test result, a vaginal pH >4.5, vaginal leukocytosis, and recurrent (vs initial) T. vaginalis infection, with the lowest levels observed in those with the highest T. vaginalis loads.
Conclusions: The SLPI level was reduced by >50% in a T. vaginalis load-dependent manner. Future research should consider whether identifying and treating females with low levels of T. vaginalis infection (before they become wet mount positive) would prevent the loss of SLPI and impaired vaginal immunity. The SLPI level could be used as a vaginal-health marker to evaluate interventions and vaginal products.