Estrogen receptors and their roles in the immune and respiratory systems

Estrogen is an important hormone for health in both genders. It is indispensable to glucose homeostasis, immune robustness, bone health, cardiovascular health, and neural functions. The main way that estrogen acts in the cells is through estrogen receptors (ERs). The presence of specific estrogen receptors is required for estrogen to have its characteristic ubiquitous action in almost all tissues. Estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) are the major isoforms of estrogen that are highly specific in humans and enable selective hormonal actions in different tissues. This article reviews some of the observed estrogen actions and effects in different tissues and cells through these specific receptors. This ubiquitous, almost ordinary hormone may reveal itself as a significant factor that helped us to better understand the complexity of the human immune system response against respiratory infections, including the COVID-19, and especially in the current state of this painful pandemic.