Host Nectin-1 Promotes Chlamydial Infection in the Female Mouse Genital Tract, but Is Not Required for Infection in a Novel Male Murine Rectal Infection Model

Abstract

Chlamydia trachomatis is the most common bacterial sexually transmitted pathogen, but more than 70% of patients fail to seek treatment due to the asymptomatic nature of these infections. Women suffer from numerous complications from chronic chlamydial infections, which include pelvic inflammatory disease and infertility. We previously demonstrated in culture that host cell nectin-1 knockdown significantly reduced chlamydial titers and inclusion size. Here, we sought to determine whether nectin-1 was required for chlamydial development in vivo by intravaginally infecting nectin-1-/- mice with Chlamydia muridarum and monitoring chlamydial shedding by chlamydial titer assay. We observed a significant reduction in chlamydial shedding in female nectin-1-/- mice compared to nectin-1+/+ control mice, an observation that was confirmed by PCR. Immunohistochemical staining in mouse cervical tissue confirmed that there are fewer chlamydial inclusions in Chlamydia-infected nectin-1-/- mice. Notably, anorectal chlamydial infections are becoming a substantial health burden, though little is known regarding the pathogenesis of these infections. We therefore established a novel male murine model of rectal chlamydial infection, which we used to determine whether nectin-1 is required for anorectal chlamydial infection in male mice. In contrast to the data from vaginal infection, no difference in rectal chlamydial shedding was observed when male nectin-1+/+ and nectin-1-/- mice were compared. Through the use of these two models, we have demonstrated that nectin-1 promotes chlamydial infection in the female genital tract but does not appear to contribute to rectal infection in male mice. These models could be used to further characterize tissue and sex related differences in chlamydial infection.

Fig 1. Host nectin-1 is required for chlamydial shedding in intravaginally infected mice.

A) Example of genotypic characterization of nectin-1 heterozygous mice (lanes 1 and 2), nectin-1^+/+ mice (lanes 3 and 4), and nectin-1^-/- mice (lanes 5 and 6). Molecular size ladders are represented by lanes labeled “L”. Nectin-1^+/+ mice exhibit a single band at 639bp, nectin-1^-/- mice exhibit a single band at 459bp and heterozygotes exhibit bands at 639bp and 459bp. B and C) Mice were infected with either 1 x 10³ IFU (B) or 1 x 10⁶ IFU C. muridarum (C) on day 0. Swab samples from days 3 through 21 pi were used in chlamydial titer assays to determine chlamydial shedding. For panel B, n = 10 for the nectin-1^+/+ group and n = 13 for the nectin-1^-/- group. For panel C, n = 19 per group. Shedding data are reported as the average IFU/mouse +/- SEM at each day pi. Shedding data are depicted as the combined data from 2 independent experiments each. Differences in shedding between groups at each day post shedding were determined with the unpaired Student’s t-test with p<0.05 considered significant, as indicated by an asterisk (*).

Fig 2. Nectin-1^-/- female mice have fewer detectable chlamydiae in the lower genital tract.

A) Day 3 pi PCR semi-quantification of chlamydial genomes using 16s DNA normalized to host β-actin. Each group n = 4 and data are representative of 2 independent experiments. B) Day 3 pi PCR semi-quantification of chlamydial viability determined by amplification of chlamydial 16s rRNA normalized to chlamydial 16s DNA and host β-actin. A single data set was analyzed and n = 4 per group. Panels A and B are reported as average integrated intensity +/-SEM. Differences between groups were determined with the unpaired Student’s t-test with p<0.05 considered significant, as indicated by an asterisk (*). Non-significant comparisons are designated NS. C) Representative gel electrophoresis of chlamydial 16s DNA, chlamydial pre-16s RNA, and host β-actin PCR bands from one nectin-1^+/+ and one nectin-1^-/- female mouse.

Fig 3. Nectin-1^-/- female mice have fewer detectable chlamydial inclusions in cervical tissue.

A) Immunohistochemical staining of nectin-1^+/+ (upper panels) and nectin-1^-/- (lower panels) C. muridarum infected cervical tissue harvested day 6 pi; n = 5 for each group. Yellow arrows indicate chlamydial inclusions. All mouse cervical samples were stained and cervical samples shown are from two individual mice per experimental group. Data are representative of two independent experiments.

Fig 4. Nectin-1 is not required for male mouse rectal chlamydial infection.

Male mice were rectally infected with 1x10⁶ IFU C. muridarum as described in the methods. A) Swab samples every 3 days from day 3 to 24 pi were used in chlamydial titer assays to determine chlamydial shedding. N = 16 and n = 18 for nectin-1^+/+ and nectin-1^-/- groups, respectively. Shedding is reported as the average IFU/mouse +/- SEM at each day pi. Combined data from two independent experiments are shown. B) Immunohistochemical staining of male wild type colon tissue at 430x (left panels) and 630x (right panels). Yellow arrows indicate chlamydial inclusions. Colon tissue was harvested from C. muridarum rectally infected mice at day 24 pi; n = 3. Two representative inclusions are depicted from one wild type mouse. Data represent a single experiment.