27,28,31,32 The cationic nature of SLPI may also allow it to directly destabilize viral envelop. The mechanism for Elafin inhibition of HIV-1 is unknown, but may be similar to SLPI given their homology (approximately 40%).29,30 Lysozyme, another component of FRT secretions, derives its antibacterial activity from the ability to cleave peptidoglycan present on bacterial cell walls.13 Like
other antimicrobials, it can directly interact with cell membranes via its positively charged amino acids.13,33 It inhibits HIV-1 infection of target cells, most likely via its HL9 and HL18 peptide regions, by blocking viral entry and replication.8,34,35 Lactoferrin, EGFR inhibitor a homolog of the iron-carrier Metformin purchase protein transferrin, inhibits bacterial growth by sequestering
iron under acidic conditions similar to those in the lower FRT.13 It blocks HIV-1 infection of target cells by interfering with viral fusion and entry through interactions with the V3 loop of HIV-1 gp120.8,36 Furthermore, it inhibits HIV-1 adsorption to target cells. MIP3α/CCL20 is a neutrophil chemoattractant, and similar to other chemokines and cytokines, also functions as an antimicrobial agent.37 Recently, it was shown to inhibit HIV-1 infection of target cells through an unknown mechanism.38 The pioneering studies of Schumacher in the 1960s and 1970s demonstrated that components of the reproductive tract milieu vary with specific stages of the menstrual cycle. For example, IgG and IgA in cervical mucus both decrease at ovulation but remain elevated during the proliferative and secretory phases of the cycle. Reflecting this initial work, other investigators have shown that, in addition to antibodies, specific cytokines, chemokines and antimicrobials also change with the menstrual Cyclooxygenase (COX) cycle. As seen in Table III, HNPs 1–3, HBD2, lactoferrin,
and SLPI in cervico-vaginal lavages (CVL) transiently and dramatically decrease at mid-cycle/ovulation, before increasing during the latter portion of the secretory phase.39,40 A similar trend for lysozyme has also been reported elsewhere.41 The greatest decreases were observed in HNPs 1–3 (80%) and HBD2 (70%).39 Multiple cytokines, which potentially have antimicrobial activity,37 also demonstrated this trend.39 Some of the highest concentrations of antimicrobials (HNPs 1–3, HBD2 and SLPI) were detected during the menstrual phase. However, this is likely due to blood contamination of CVL during endometrial breakdown and may not reflect endogenous FRT production. In contrast to CVL findings, studies using tampons for collection of vaginal fluid reported increased levels of HNPs 1–3, HBD2, and lysozyme while lactoferrin, HBD1, and SLPI decreased from proliferative to secretory stages of the menstrual cycle with no apparent mid-cycle drop.