CD4 and HIV infectious disease: In addition, preclinical trials reported by Mansueto et al., showed that treatment of peripheral blood monocytes with 1,25 (OH) 2D (the active form of vitamin D) reduced the sensitivity of cells to HIV infection by inhibiting viral entry, regulating the expression of CD4+ cell surface antigens, inhibiting the production of viral p24, and restricting the proliferation of monocytes [53].