Investigating the effect of sex hormones on sexual dimorphism in the lung tissue microenvironment

Abstract

Sex differences in prevalence, morbidity and mortality of lung diseases are well established. For example, adult women are more susceptible to influenza infection and chronic obstructive pulmonary disease. On the other hand, adult men experience worse outcomes in pneumococcal pneumonia and squamous cell carcinoma. Although sex hormones have been proposed to account for such sex differences, their exact impact on local tissue microenvironment, lung function and thus, the pathogenesis of lung diseases has not been fully clarified. Major compartments of the lung tissue microenvironment are the respiratory epithelium and the lung resident immunity. Given the fact that hormone receptors, including estrogen and androgen receptors, are expressed both on most immune cell subtypes and on the respiratory epithelium, sex hormones may affect lung tissue resident immunity in a sex specific manner, subsequently leading to a sex-specific manifestation of respiratory immune diseases. Our aim was to investigate sex differences in the lung tissue microenvironment, including lung resident immunity and the respiratory epithelium, and identify the potential role of sex hormones in this context. To this aim, firstly, through flow cytometry of cells isolated from the lung of male and female adult C57BL/6 mice, we characterized the sexual dimorphism of tissue-resident immunity in the naïve lung. Our next step was to investigate the impact of sex hormones on lung tissue resident immunity. Male and female mice underwent castration or ovariectomy, respectively and after 14 days the mice were sacrificed and their lungs were collected for immune characterization with flow cytometry or histological assessment of the integrity of the respiratory epithelial barrier. Finally, an assessment of lung resident immunity was also performed upon testosterone supplementation of female mice. Our results indicate that males have increased alveolar macrophages and lung-residing monocytes, while females have more lung resident CD103+ DCs, pDCs and CD4+ TRM cells. Castration resulted in a reduction of lung resident DCs, infiltrating monocytes, interstitial macrophages and lung resident NK cells, while infiltrating B and CD8+ cells in the lung were intensively augmented. In line with these findings, B cells were also significantly decreased and neutrophils increased after testosterone supplementation of female mice. No profound alterations in lung resident immunity were observed after ovariectomy. This study indicates the existence of sex differences in the lung microenvironment which are likely mediated by sex hormones. These findings shed light into the sex-specific manifestation of respiratory immune diseases and could set the basis for novel personalized therapeutic approaches in this context.