Katherine Forsyth

"A novel role for X-Chromosome Inactivation in regulating T cell responses to Influenza"

Katherine Forsyth and Montserrat Anguera

Women mount stronger immune responses during various infectious diseases caused by viruses and bacteria. For influenza infections, pre-puberty and elderly men are most susceptible, yet pre-menopausal women are more at risk compared to men of similar age. Sexual dimorphism in immune responses has both hormonal and genetic origins, and while sex hormone signaling has been implicated in differential susceptibility to influenza, the genetic contribution has not been investigated. Female XX mammalian cells use random X-Chromosome Inactivation (XCI) to normalize X-linked gene expression with male XY cells. XCI is established early in female embryonic development and maintained through each subsequent cell division. XCI is initiated by expression of the lncRNA Xist from the inactive X (Xi) which forms a cytologically detectable ‘cloud’ around the Xi and recruits repressive chromatin complexes to the Xi. While XCI maintenance was thought to be a static process, we determined that mature T cells, unlike most somatic cells, have an unusual and dynamic mechanism for XCI maintenance, where Xist RNA clouds and repressive histone modifications only become localized to the Xi upon stimulation. Because the X chromosome contains many immunity-related genes important for T cell function, we hypothesize that perturbations with XCI maintenance in T cells will affect T cell function and responses to influenza infection. Using a novel mouse model where Xist is specifically deleted in T cells (CD4cre+ Xistfl/fl mice) we demonstrate here that perturbation of XCI maintenance in T cells results in enhanced protection from sublethal influenza challenge. While anti-influenza neutralizing antibody titers are comparable to controls, T cells in the lungs of CD4cre+ Xistfl/fl mice have elevated expression of the X-linked chemokine receptor CXCR3, a critical protein for effector T cell extravagation into the lungs. However, we also found that CD4cre+ Xistfl/fl mice are more susceptible to a LD50 influenza challenge. Together, these data suggest that perturbation of XCI maintenance in T cells leads to heightened cellular functionality that is protective against low viral load but immunopathologic at high viral load. These data and ongoing experiments to further mechanistically characterize the X-linked genes involved in this phenotype will demonstrate for the first time genetic contributions from the X play a role in sex differences with influenza infection and resulting disease pathologies.