IL-33 Mediated Th2 Effector Functions are Suppressed in Tregs by Bcl6 and Regulated by Sex

Abstract

Allergic airway inflammation (asthma) is a prevalent and uncurable disease worldwide, affecting many individuals’ quality of life. Although asthma does not form from a singular cause, one primary mediator comes from the exposure to environmental allergens and the improper activation of the T cell subset: T helper 2 (Th2) cells. Th2 cells produce pro-inflammatory cytokines and promote the activation and recruitment of various pro-inflammatory cells into the lung, causing greater damage and inflammatory responses in the organ. Th2 cell’s activation is regulated by another T cell subset, Regulatory T (Treg) cells, by expressing anti-inflammatory cytokines and downregulating the inflammatory response. On the contrary, the release of interleukin-33 (IL-33) from damaged lung epithelial cells transitions Tregs into Th2-like Tregs (ST2+ Tregs) which release both pro-and anti-inflammatory cytokines and cannot suppress the inflammatory disease. However, transcriptional repressor protein B cell lymphoma 6 (Bcl6) provides Tregs a stable follicular phenotype and suppresses the ST2+ Treg transition. Preliminary data revealed that Bcl6 repressive function is dependent on mouse sex, in which Tregs of male mice are more resistant to the ST2+ Treg phenotype than those of female mice. However, the removal of Bcl6 also removed the sex-dependent suppression against the ST2+ Treg transition. The project therefore sought to further confirm and answer whether Bcl6 suppressed the ST2+ Treg phenotype in a sex-dependent manner, ultimately leading to a sex-biased asthma prevalence and severity. We utilized quantitative polymerase chain reaction (qPCR) and next-generation sequencing techniques to uncover which genes Bcl6 regulates, how IL-33 affects chromatin accessibility/gene expression, and what relation sex hormones have with Bcl6 in the expression of Th2 cytokines from Tregs. Currently, we have discovered that estrogen-like chemicals in common cell culturing media may be acting on the estrogen receptor of Tregs and causing differential gene expressions based on media conditions. We also determined that Bcl6 is acting independently of mouse sex to suppress Th2 genes in Tregs, contrary to preliminary findings. Overall, we have obtained insight on the role of the estrogen receptor and Bcl6’s mechanism of suppression in relation to sex.