Effects of hormone replacement therapy on immunological factors in the postmenopausal period

Background: Despite valuable evidence documented on immunological changes in postmenopausal women, particularly following hormone replacement therapy (HRT), it is difficult to explain whether immunological changes during menopause are caused by HRT. This systematic review aimed to summarize the results of studies available on postmenopausal immunological changes and to determine any potential effects of HRT on the immunological profile of postmenopausal women. Methods: For this systematic review, we primarily explored 751 papers about the immune system status of postmenopausal women published during 1955-2015. Scientific databases including Web of Science, MEDLINE, Scopus, Embase, Google Scholar, and the Cochrane database were searched for a number of relevant key terms. Of 209 papers that met the initial search criteria, 13 papers were potentially retrievable and included descriptions of changes in immunological factors during the postmenopausal period and the effects of HRT on such changes. Results: HRT resulted in a range of immunological changes in postmenopausal women. These changes included reductions in interleukin-2 (IL-2), IL-6, and insulin-like growth factor-1 levels and increments in IL-1 and IL-4 levels. Elevations in B-cell production and estrogen receptor alpha, CD19+ cells, and C3 and C4 complement levels were also documented. Decreased CD8+ counts were also a constant finding in most reviewed papers. However, data on the changes in other factors such as tumor necrosis factor-alpha, interferon-gamma, CD4+, and CD25+ were contradictory. Levels of some immunological factors, e.g. immunoglobulin G (IgG), IgM, and IL-10, remained unchanged following HRT. Conclusion: Postmenopausal women are prone to impaired immune responses. HRT during the menopausal period can mediate immunological responses by inducing significant changes in immunological mediators.