Mycoplasma genitalium -Encoded MG309 Activates NF-κB via Toll-Like Receptors 2 and 6 To Elicit Proinflammatory Cytokine Secretion from Human Genital Epithelial Cells

Abstract

Mycoplasma genitalium has been implicated in several important reproductive tract syndromes in women, including pelvic inflammatory disease, cervicitis, and tubal factor infertility. The mechanisms of immune activation are unclear, and we sought to determine whether M. genitalium was capable of activating innate immune responses through ligation of highly expressed Toll-like receptors (TLR) of the genital tract. Using HEK293 cells expressing specific human TLR, viable M. genitalium and the recombinant C-terminal portion of the immunogenic protein MG309 (rMG309c) were shown to activate NF-B via TLR2/6. These data provided a putative mechanism for activation of the innate response in genital tissues. Genital epithelial cells (EC) are the first responders to sexually transmitted pathogens and express high levels of TLR2 and -6. Following exposure to purified rMG309c, vaginal and ecto-and endocervical EC secreted proinflammatory cytokines, including interleukin-6 (IL-6) and IL-8. Vaginal EC were less responsive than cervical EC. The capacity of rMG309c to bind TLR2/6 and elicit inflammation was sensitive to proteinase K digestion and independent of traditional N-terminal lipoylation. Furthermore, the immunostimulatory capacity of rMG309c was localized specifically to a 91-amino-acid subfragment of the recombinant protein, suggesting that TLR activation is likely amino acid based. Together, these data indicated that human vaginal and cervical EC are immunologically responsive to M. genitalium and to purified rMG309c via highly expressed TLR of the genital tract. These findings provide valuable insights into the mechanisms for activation of acute-phase inflammatory responses and suggest that M. genitalium colonization of reproductive tract tissues may result in inflammatory sequelae.Mycoplasma genitalium is a sexually transmitted pathogen (20, 27) implicated as an important cause of nongonococcal urethritis in men (28). In women, inflammatory reproductive tract disease syndromes, including pelvic inflammatory disease (17) and cervicitis (11,24,26,34,44), also have been associated with M. genitalium infection. However, the mechanisms for initiation of the innate immune response in these tissues have yet to be elucidated. Results presented herein establish that M. genitalium and the C-terminal portion of the antigenic protein encoded by MG309 activate NF-B via Toll-like receptors 2 and 6 (TLR2/6), resulting in cytokine secretion from relevant epithelial cells (EC) of the reproductive tract. These findings elucidate a putative mechanism for induction of proinflammatory responses and provide a rationale for continued investigation into the mechanisms of M. genitalium-induced urogenital disease in women.The female reproductive tract includes the normally sterile upper genital tract, composed of the uterus, fallopian tubes, and ovaries. The lower genital tract includes the polymicrobial environment of the vagina and the translational ectocervical and endocervical tissues. EC of the reproductive tract provide a physical barr...

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