Air Pollution and Inflammation: Findings from Concurrent Repeated Measures of Systemic and Reproductive Tract Cytokines During Term Pregnancy in Mexico City

Background: Environmental exposures are associated with a number of outcomes including adverse pregnancy outcomes. Although inflammation is hypothesized to play a role, the mechanistic pathways between environmental exposures and adverse health outcomes, including associations between exposures and longitudinal measures of systemic and reproductive tract inflammation, need elucidation.

Objectives: This study was conducted to evaluate whether exposure to air pollution is associated with immunologic responses in the systemic circulation and lower reproductive tract, and to evaluate whether systemic and reproductive tract immunologic responses are similar.

Methods: We quantified repeated measures of cytokines from cervico-vaginal exudates and serum obtained concurrently among 104 women with term pregnancies and estimated PM and CO exposure using the monitor nearest each participant's residence. Serum and cervico-vaginal cytokines were compared using Wilcoxon signed-ranks test and Spearman rank correlations for select gestational months. We used intraclass correlation coefficients (ICCs) to quantify reproducibility of cytokine measurements, and Tobit regression to estimate associations between air pollution and cytokines.

Results: Median cervico-vaginal levels of IL-6, Eotaxin, IP-10, MCP-1, MIP-1α, MIP-1β, and TNFα were higher than corresponding serum cytokines, significantly so for IL-6 and IP-10. Cervico-vaginal and serum cytokines were not correlated, but cytokines from the same fluid were correlated. ICCs for most serum cytokines were ≤0.40, while ICCs were higher in cervico-vaginal cytokines (range 0.52-0.83). IP-10 and Eotaxin had the highest ICCs for both cytokine sources. In adjusted models, PM was positively associated with serum cytokines IL-6, IP-10, MIP-1β and Eotaxin but inversely associated with cervico-vaginal cytokine TNFα, IP-10, MIP-1β, MCP-1 and Eotaxin, controlling for false discovery rate. CO was inversely associated with cervico-vaginal TNFα, IL-6, MIP-1β, MCP-1 and Eotaxin.

Conclusions: Inflammatory processes are compartment-specific. Systemic inflammatory markers may provide information on immunologic processes and response to environmental exposures, but are not proxies for lower reproductive tract inflammation.