Active and precursor forms of Vitamin D reduce HIV-1 infection in vitro

BACKGROUND:: Although the anti-HIV-1 effects of Vitamin D (VitD) have been reported, mechanisms behind such protection remain largely unexplored. METHODS:: Effects of active VitD (calcitriol) at 10, 10 and 10 M or its precursor (calcidiol) at 100 and 250 nM, on HIV-1 infection, immune activation and gene expression were analyzed in vitro in cells of Colombian and Italian healthy donors, respectively. We quantified levels of released p24 by ELISA, of intracellular p24 and cell-surface expression of CD38 and HLA-DR by flow cytometry, and mRNA expression of antiviral and immunoregulatory genes by qRT-PCR. RESULTS:: Calcitriol decreased the frequency of HIV-1-infected p24CD4 T-cells and levels of p24 in supernatants in a dose-dependent manner. Moreover, the CD4CD38HLA-DR and CD4CD38HLA-DR subpopulations were more susceptible to infection, but displayed the greatest calcitriol-induced decreases in infection rate by an X4-tropic strain. Likewise, calcitriol at its highest concentration decreased the frequency of CD38HLA-DR but not of CD38HLA-DR T-cell subsets. Recreating a physiological scenario using calcidiol, the main VitD source for immune cells, and an R5-tropic strain as the most frequently transmitted virus, a reduction in HIV-1 productive infection was also observed. In addition, an increase in mRNA expression of APOBEC3G and PI3, and a reduction of TRIM22 and CCR5 expression, this latter positively correlated with p24 levels, was noted. CONCLUSIONS:: VitD reduces HIV-1 infection in T cells possibly by inducing antiviral gene expression, reducing the viral co-receptor CCR5 and, at least at the highest calcitriol concentration, by promoting an HIV-1-restrictive CD38HLA-DR immuno-phenotype.