Vitamin D and Particulate Matter–Associated Immune Responses in People Living with HIV: A Randomized Trial with Exploratory DNA Methylation Analyses

Background: HIV-infected individuals with compromised immune function are particularly vulnerable to atmospheric particulate matter (PM). While Vitamin D is known to modulate inflammation and immune function, its effect on PM-induced immune impairment in HIV-infected individuals remains unclear. Methods: This randomized, double-blind, placebo-controlled trial in Wuhan, China, investigated Vitamin D’s protective effects. In total, 80 participants received daily Vitamin D or a placebo and were followed up every 28 days across four visits. PM exposure was assessed 72 h before each follow-up, with immune cell counts, immunomodulatory factors, and whole-genome DNA methylation profiles measured. Linear mixed-effects models were used to assess the association between PM exposure and cell counts, and to identify CpG sites associated with Vitamin D. Mediating models further evaluated the role of these CpG sites in linking Vitamin D intervention to cytokine changes. Results: From March to July, 2023, 75 participants received 271 follow-ups. Vitamin D supplementation significantly attenuated the negative associations between PM exposure and CD4+T cell and CD19+B cell counts. Compared with the placebo group, the estimated PM-associated changes in CD4+T cell counts differed by 3.37%, 2.21%, and 1.96% per 10 µg/m3 increase in PM1, PM2.5, and PM10 concentrations, respectively, while the corresponding differences for CD19+B cell counts were 4.71%, 2.98%, and 2.65%, respectively. Significant methylation changes were observed at 173 CpG sites related to Vitamin D. Of these, 25 sites—including cg27066321 (PEX14), cg08500112 (PDE4D), and cg25882580 (CACNG6)—were identified as potential mediators of the effects of vitamin D supplementation on TLR4, IL-6, and TNF-α levels, with mediation proportions ranging from 27.98% to 78.78%. Conclusions: Vitamin D supplementation may attenuate PM-associated immune alterations in people living with HIV, with DNA methylation potentially contributing to the underlying mechanisms.