ABSTRACT Asthma is a lung disease caused by exaggerated lung inflammation leading to airway obstruction and compromised airflow. Despite significant advances in its diagnosis and treatment, asthma continues to be a significant health problem affecting more than 25 million patients in the US, and over 300 million around the world. Well-characterized sex and gender differences in asthma have been reported, with changes in morbidity throughout life. Starting around puberty and peaking during mid-life, women have increased asthma prevalence and higher rates of asthma exacerbations than men. Causes of these disparities remain unclear; however, studies have shown that sex-specific inflammatory mechanisms controlled by hormones contribute to differences in airway reactivity in response to environmental stimuli. Despite this, experimental models of asthma have not explored the contributions of sex hormones to inflammatory mechanisms in the female and male lung, and no studies have explored the effects of feminizing hormone therapy with estrogen in the lungs of trans women. Prior studies from our laboratory using mouse models have reported sex differences and influences of the estrous cycle and circulating sex hormones in the inflammatory response to environmental exposures. Based on these findings, we hypothesized that female sex hormones, specifically estrogens, contribute to asthma phenotypes in the lung via activation of inflammatory mechanisms mediated by estrogen receptors. In the proposed study, we will test this hypothesis by determining the mechanisms by which estrogen mediates sex and gender influences in asthma. In Aim 1, we will determine the contributions of sex chromosome complement (XX vs. XY) vs. gonadal hormones in asthma phenotypes, by developing a mouse house dust mite (HDM) asthma model on the four core genotypes (FCG) model. In Aim 2, we will study the contributions of estrogens to HDM-induced asthma outcomes using male and female gonadectomized mice treated with estradiol, as well as bronchial epithelial cells from male and female healthy and asthma patients to exposed to HDM in the presence/absence of estrogen receptor agonists/antagonists. In Aim 3, we will determine the roles of nuclear (ER) and membrane- bound (GPER-1) estrogen receptors in estrogen-mediated mechanisms of inflammation in HDM-induced asthma, using ER and GPER1 knockout mice. Our studies will be the first to characterize estrogen-mediated mechanisms of inflammation in asthma phenotypes in the male and female lung, contributing to the characterization of sex- and gender-specific factors accounting for inter-individual differences, as well as the effects of feminizing hormone therapy in lung pathobiology. We expect that our studies would serve to develop potential sex- and gender-specific treatments and recommendations for dosage of therapeutic agents to treat and prevent asthma in cis and transgender women.