Associations of current and birthplace region with immunity in later life in the health and retirement study.

The United States has well-documented regional disparities in health outcomes. Functioning of the immune system is highly influenced by the environment, suggesting that geographic variation in immune cell composition maybe an underlying factor behind health disparities. This study examines whether current and birth region of residence is associated with markers of immune aging in a nationally representative sample of older adults. We analyzed immune cell subsets from 8472 participants measured in the 2016 wave of US Health and Retirement Study. Two-level regression models accounting for census-tract clustering were used to evaluate the impact of current and birth region of residence on immune cell counts after adjustment for sociodemographic and health behavioral factors as well as CMV seropositivity. Southern residents had a nominally lower count of CD4+ naïve T cells (0.325 < 0.336; p = .084) and a higher count of CD4+ central memory T cells (0.286 > 0.274; p = .004). Individuals born in the South had lower counts of CD4+ naïve T cells (0.321 < 0.343; p = .006) but higher counts of CD4+ central memory T cells (0.288 > 0.271; p = .001), and the differences remained significant even upon additional adjustment for current residence. Similar patterns were observed among individuals who stayed in the South compared to those who either stayed outside the South or relocated there. Our study reveals that birth region of residence plays a stronger role in shaping the immune profile of older adults than current region, which indicates that early exposures may leave a lasting imprint on immune profiles.