Bacterial vaginosis (BV) is a vaginal syndrome characterized by an overgrowth of anaerobic vaginal bacteria, and is associated with several adverse clinical outcomes, including pelvic inflammatory disease, preterm birth and increased risk of HIV-1 acquisition. The individual bacterial species differ between individuals, as do the clinical symptoms, the incidence of serious sequelae, and patterns of cytokine response. We hypothesize that clinical differences result from the interactions between individual species and host immune responses. We plan to test the following hypotheses: 1) that some bacterial species downregulate the innate host response, allowing high levels of colonization by decreasing levels of vaginal cytokines and/or production of antimicrobial peptides(beta-defensins, cathelicidin, secretory leukocyte protease inhibitor[SLPI], lactoferrin); 2) that some individuals are more vulnerable to colonization due to low baseline levels of those antimicrobial peptides; 3) that Lactobacillus species and BV-associated pathogens activate the innate immune response differently via pattern-recognition receptors like TLR-2; and 4) that some bacterial species are more likely to colonize the upper genital tract due to the presence of virulence factors or mechanisms for subverting the host immune response. We will characterize prospectively collected daily vaginal swabs from 30 women for levels of individual bacterial species using qPCR for the 16S rRNA gene, and correlate these with the temporal response in levels of cytokines and antimicrobial peptides (Aim 1). Responses in vaginal epithelial cell culture will be used to determine whether lactobacilli and BV-associated microbes activate toll-like receptors differently resulting in different cytokine profiles, and whether TLR-2 activation is associated with higher levels of antimicrobial peptides (Aim 2). Endometrial samples collected at hysterectomy will be characterized by broad range 16S rRNA PCR and pyrosequencing to detect upper genital tract colonization and define the microbiota in comparison to the vaginal microbiota in the same women. In addition, levels of cervical cytokines and defense molecules will be measured to assess their relationship with upper tract colonization (Aim 3). The PI for this application, Caroline Mitchell, MD is an OB/Gyn whose goal is to understand how the female genital tract defends against bacterial pathogens, with the ultimate endpoint of developing better therapeutic and preventive interventions. Her mentor, Dr. David Fredricks, is a nationally recognized investigator known for using advanced molecular techniques to better characterize the vaginal microbiota, and has recently been recognized for excellence in mentoring. The University of Washington is the top public university for research funding, with an internationally-renowned Infectious Diseases program and a long history of studies on BV. The scientific advisory committee has expertise in immunologic techniques, clinical trials and data analysis. Narrative: Bacterial vaginosis is a common clinical syndrome that affects up to 30% of women in the United States and is associated with a 2-fold increase of the risk of preterm birth, pelvic inflammatory disease and HIV-1 acquisition. This project will increase our understanding how certain bacterial species change the risk of acquiring bacterial vaginosis and what components of the immune response are most important for protection against bacterial vaginosis. This will allow development of targeted preventive and therapeutic interventions to reduce the adverse clinical outcomes.