Chlamydial Pre-Infection Protects from Subsequent Herpes Simplex Virus-2 Challenge in a Murine Vaginal Super-Infection Model

Abstract

Chlamydia trachomatis and Herpes Simplex Virus-2 (HSV-2) genital tract co-infections have been reported in humans and studied in vitro but the clinical consequences are unknown. Limited epidemiologic evidence suggests that these co-infections could be more severe than single infections of either pathogen, but the host-pathogen interactions during co-infection remain uncharacterized. To determine whether disease progression and/or pathogen shedding differs between singly-infected and super-infected animals, we developed an in vivo super-infection model in which female BALB/c mice were vaginally infected with Chlamydia muridarum (Cm) followed later by HSV-2. Pre-infection with Chlamydia 3 or 9 days prior to HSV-2 super-infection conferred significant protection from HSV-2-induced neurologic disease and significantly reduced viral recovery compared to HSV-2 singly-infected controls. Neither protection from mortality nor reduced viral recovery were observed when mice were i) super-infected with HSV-2 on day 27 post Cm; ii) infected with UV-irradiated Cm and super-infected with HSV-2; or iii) azithromycin-treated prior to HSV-2 super-infection. Therefore, protection from HSV-2-induced disease requires active infection with viable chlamydiae and is not observed after chlamydial shedding ceases, either naturally or due to antibiotic treatment. Thus, Chlamydia-induced protection is transient and requires the continued presence of chlamydiae or their components. These data demonstrate that chlamydial pre-infection can alter progression of subsequent HSV-2 infection, with implications for HSV-2 transmission from co-infected humans.

Type I IFNs in the female reproductive tract: The first line of defense in an ever-changing battleground

“…82 More recently, it has been found that microbial metabolites produced during Chlamydia infection not only induce expression of type I IFN via STING, they also activates inflammasome responses. 83 Interestingly, preinfection of mice with Chlamydia protects against subsequent infection with HSV-2, 84 which may be due to the initial Chlamydia infection driving expression of type I IFN in the FRT and the associated antiviral responses. In vitro, stimulation of infected cells with IFN or IFN can limit replication of Chlamydia bacteria through depletion of intracellular iron and induction of bactericidal IDO, nitric oxide synthase and IFN-, reviewed in Ref.…”

The Type I Interferon Receptor is Not Required for Protection in the Chlamydia and HSV-2 Murine Super-infection Model

“…At 8–10 weeks of age, mice were intravaginally infected with 1 × 10 6 IFU C. muridarum on day 0 and/or with 1 × 10 5 PFU HSV-2 on day 3 post chlamydial infection (pci) as previously described (Slade et al. 2016 ). To monitor pathogen shedding, mice were vaginally swabbed every 3 days until day 21 pci as described elsewhere (Phillips Campbell et al.…”

“… 2012 ; Slade et al. 2016 ). Processed samples were used to determine pathogen shedding via the chlamydial titer assay and via plaque assay for HSV-2 as described (Slade et al.…”

“…Processed samples were used to determine pathogen shedding via the chlamydial titer assay and via plaque assay for HSV-2 as described (Slade et al. 2016 ). Data are expressed as the average inclusion-forming units/mL and plaque-forming units/mL +/– SEM, respectively.…”

“…We determined that mice intravaginally infected with Chlamydia followed either 3 or 9 days later with HSV-2 infection exhibit significantly increased survival and significantly reduced viral shedding compared to animals singly infected with HSV-2 (Slade et al. 2016 ). In other words, chlamydial pre-infection protects from subsequent HSV-2-induced mortality and disease.…”