The impact of irritant challenge on the skin barrier and myeloid resident immune cells in post-menopausal women is modulated by hormone replacement therapy

Background: Sex hormone changes during menopausal transition contribute to declining skin health. However, how menopause and its treatment by hormone replacement therapy (HRT) impact the skin barrier and immune system is unclear. Therefore, we examined how menopause and HRT affect skin barrier and immune cell composition in post-menopausal women following irritant challenge.
Methods: Two cohorts of post-menopausal women were recruited to the study, one untreated (HRT^-; n = 10; mean age 56.5 yrs [range 48 – 63 yrs]) and the other receiving HRT (n = 8; mean age 54 yrs [range 48 – 63 yrs]). Skin irritation was induced by applying 1.25% topical Sodium Lauryl Sulfate (SLS) to occluded buttock skin for 48 hours. Clinical assessment was conducted after 24 hours, followed by biopsy of both SLS-challenged and unchallenged skin for analysis of skin barrier proteins and immune cell distribution using immunofluorescence.
Results: Clinically, there were no significant differences in skin irritant responses between those taking or not taking HRT (including increased skin redness and blood flow). In response to SLS challenge a significant increase in trans-epidermal water loss (p<0.05), filaggrin deposition and keratin-10-positive cell layers (p<0.01) was observed in individuals receiving HRT compared to the HRT^- group. Following SLS challenge in individuals taking HRT, a significant (p<0.01) reduction of CD207⁺ cells in the epidermis was observed, accompanied by an increase of CD207⁺ cells in the dermis, indicative of migrating Langerhans’ cells (LCs). Significantly fewer migrating LCs were observed in those not receiving HRT (p<0.01). Furthermore, the number of dermal dendritic cells (DCs), macrophages, and CD11c⁺CD206^- and CD68⁺CD206^- subsets were found to be significantly (p<0.05) higher in those taking HRT following SLS challenge.
Conclusion: Individuals receiving HRT displayed enhanced skin barrier response to SLS challenge with thicker filaggrin and increased keratin-10-positive epidermal cell layers. Following challenge, HRT users exhibited elevated counts of LCs, inflammatory DCs, and macrophages in the dermis. These may render skin both, more prone to inflammation and more capable of resolving it, while also promoting skin repair.