Impact of the Levonorgestrel-Releasing Intrauterine System on the Progression of Chlamydia trachomatis Infection to Pelvic Inflammatory Disease in a Baboon Model

Abstract

Background: Understanding the relationship between the levonorgestrel (LNG)-releasing intrauterine system (IUS) and sexually transmitted infections (STIs) is increasingly important as use of the LNG-IUS grows to include women at higher risk for STIs. This study assessed the impact of the LNG-IUS on development of Chlamydia trachomatis pelvic inflammatory disease, using a baboon model.

Methods: Baboons with and those without the LNG-IUS were cervically inoculated with C. trachomatis and monitored daily, and cervical and fallopian tube swab specimens were collected weekly for C. trachomatis quantitation by nucleic acid amplification testing and culture. Vaginal swab specimens were collected for cytokine analysis, and serum samples were obtained for detection of C. trachomatis antibodies.

Results: The LNG-IUS resulted in an increased C. trachomatis burden in the cervix, with the bacterial burden in the LNG-IUS group diverging from that in the non-LNG-IUS group by 6 weeks after infection. One of 7 baboons in the non-LNG-IUS group and 2 of 6 in the LNG-IUS group developed pelvic inflammatory disease, while 3 animals in each group met criteria suggestive of pelvic inflammatory disease. LNG-IUS increased baseline interleukin 8 levels but failed to further upregulate interleukin 8 during infection. In LNG-IUS recipients, early perturbations in the interleukin 1β axis corresponded to decreased C. trachomatis clearance and increased T-helper type 2 immune responses.

Conclusion: LNG-IUS use results in delayed clearance of C. trachomatis and might alter the reproductive tract immune environment.

Keywords: Chlamydia trachomatis; baboon; immune responses; intrauterine contraception; levonorgestrel.

Figure 1.

Chlamydia trachomatis bacterial burden between baboons with and those without the levonorgestrel (LNG)–releasing intrauterine system (LNG-IUS). A, Baseline monitoring, equilibration, infection, and sampling schematic. All animals had 4 weeks of baseline monitoring with laparoscopic examination, followed by weekly sampling of the lower female reproductive tract. Baboons randomly assigned to the LNG-IUS group had a 24-week equilibration period, with sampling every 4 weeks before infection at week 0. Baboons in the non-LNG group did not have the 24-week IUD equilibration period and were inoculated with C. trachomatis immediately after the baseline monitoring period. All infected animals received 5 cervical inoculations of 1 × 10⁷ inclusion-forming units of serovar E C. trachomatis. During the infection period, animals had samples collected noninvasively each week and were monitored laparoscopically every 4 weeks until necropsy at 16 weeks after infection. B, Quantitative nucleic acid amplification testing was performed weekly during infection on cervical samples obtained from animals. Green arrows indicate the multiple inoculation time course. Data are for 6–7 animals per time point. EB, elementary body. *P < .05.

Figure 2.

Representative fallopian tube histological staining with hematoxylin and eosin for uninfected animals, animals with pelvic inflammatory disease (PID), and animals with lower reproductive tract infection, by levonorgestrel (LNG)–releasing intrauterine system (LNG-IUS) receipt. PID, when present, was manifested as leukocyte infiltration to the tubal propria (salpingitis). A and B, Uninfected animals without (A) and with (B) the LNG-IUS, showing high magnification of thin tubal propria lined by epithelium (inset shows the low-magnification overview). C and D, Infected animals positive for PID, showing infiltrating leukocytes (long arrows) in animals without (C) and with (D) an LNG-IUS. Leukocyte infiltration is seen as proprial thickening (short arrows) at low magnification (insets) in both animals. E and F, Infected animals with infection confined to the lower reproductive tract, showing normal thin propria (similar to uninfected controls) in animals without (E) and with (F) an LNG-IUS. See the text for a description of leukocytic infiltrations. Scale bars denote 70 um (panels) and 700 um (insets).

Figure 3.

Cytokine responses to Chlamydia trachomatis infection at baseline and during infection. Vaginal swab specimens were collected weekly for cytokine analysis. A, Baseline interleukin 1RA (IL-1RA) production was high in nonrecipients of the levonorgestrel (LNG)–releasing intrauterine system (the non-LNG group) but was repressed after C. trachomatis infection; the LNG-IUS group had low expression of IL-1RA at baseline and during infection. B, Interleukin 1β (IL-1β) production increased immediately after C. trachomatis infection in the non-LNG group and remained increased until infection began to clear; the LNG-IUS group had delayed production of IL-1β. C, The interleukin 8 (IL-8) level was significantly elevated at baseline in the LNG-IUS group in the absence of infection. D, Induction of IL-8, expressed as the fold increase from the baseline level, increased in the non-LNG group, while the LNG-IUS group, which had high baseline IL-8 levels, had decreased production of IL-8 during infection, relative to their baseline levels. Data are for 6–7 animals sample (some points are superimposed). NS, not significant; ND, none detected. *P < .05; **P < .01.

Figure 4.

Effect of levonorgestrel (LNG) on T-helper type 1 (Th1)/Th2 polarization during infection. Vaginal swab specimens were collected weekly for cytokine analysis. Baseline values represent the cytokine environment immediately before infection and were compared to cytokine values 1 week after infection. Animals that received the LNG-releasing intrauterine system (LNG-IUS) had induction of the primarily Th2-recruiting chemokine CCL2 (MCP-1) during the week after initial inoculation (ie, at week 1; A), while the non-LNG group had induction of the primarily Th1-recruiting chemokine CCL3 (MIP-1α) at week 1 (B). Week 0 corresponds to the baseline (uninfected) state. Data are for 6–7 animals per sample (some points are superimposed). *P < .05; **P < .01.