Steady-state estradiol triggers a unique innate immune response to allergen resulting in increased airway hyper-reactivity yet decreased eosinophils and ILC2.

Abstract Rationale: Asthma is a chronic airway condition that occurs more often in women than men during reproductive years. In males, testosterone attenuates allergic inflammation while estrogens are thought to exacerbate asthma through the estrogen receptors on airway epithelial cells. Population studies have looked at all types of asthma, and collectively shown that long-term use of oral contraceptives decreased the onset of asthma in women of reproductive age. In the current study, we hypothesized that steady-state levels of estrogen would reduce airway inflammation and airway hyperresponsiveness to methacholine challenge. Methods: Ovariectomized BALB/c mice (Ovx) were implanted with subcutaneous hormone pellets (estrogen, OVX-E2; or placebo, OVX-Pl) that deliver consistent levels of estrogen [49 ± pg/mL] followed by ovalbumin sensitization and challenge. In conjunction with methacholine challenge, immune phenotyping was performed to correlate inflammatory proteins and immune populations with better or worse pulmonary outcomes measured by invasive pulmonary mechanics techniques. Results: Histologic analysis showed an increase in total cell infiltration around the airways and vasculature leading to an increased inflammatory score in ovarectomized (OVX) animals with steady-state estrogen pellets (OVX-E2-OVA) as compared to other groups including female-sham operated (F-Sham-OVA) and OVX implanted with a placebo pellet (OVX-Pl-OVA). Airway resistance (Rrs) and lung elastance were increased in OVX-E2-OVA in comparison to F-Sham-OVA following aerosolized intratracheal methacholine challenges. Immune phenotyping revealed that steady-state estrogen reduced CD3+ T cells, CD19+ B cells, ILC2 and eosinophils across all experiments. Inflammatory cytokines (IL-5 and IL-13) were also decreased in OVX-E2-OVA treated animals in comparison to Female-Sham-OVA mice. ILC2 that were sorted and stimulated with exogenous IL-33 had less cytokine and chemokine expression when they were isolated from OVX-E2-OVA animals indicating that estrogen suppresses IL-33 mediated activation of ILC2. Conclusions: Therapeutically targeting estrogen receptors may have a limiting effect on eosinophils, ILC2 and potentially other immune populations that may improve asthma symptoms in those females that experience perimenstrual worsening of asthma, with the caveat, that long-term use of estrogens or hormone receptor modulators may be detrimental to the lung microenvironment over time.