Vitamin A is a key regulator for cell growth, cytokine production, and differentiation in normal B cells

In the present paper we demonstrate that retinol-retinol-binding protein and chylomicron remnant retinyl esters in concentrations normally found in human plasma inhibit growth of normal human B lymphocytes. Physiological concentrations of retinoic acid (about 30 nM) were less active than physiological concentrations of retinol (about 3 microM). Pharmacological concentrations of retinol and retinoic acid were more active than the concentrations normally found in plasma. Retinol (3 microM) inhibited anti-IgM-mediated DNA synthesis as measured by [3H]thymidine uptake at 72 h by 78%. Furthermore, we found that the cells were blocked in the mid-G1 phase of the cell cycle. Thus, neither MYC up-regulation measured at 3 h nor the expression of the early activation antigen 4F2 was reduced by retinol, whereas the late activation markers (transferrin receptor expression and actinomycin D staining at 48 h of stimulation) were markedly inhibited. Retinol reduced the interleukin 6 production induced by anti-IgM and interleukin 4 after 48 h, whereas the induction of interleukin 6 and tumor necrosis factor by O-tetradecanoylphorbol-13-acetate and ionomycin was less affected. We also noted that the retinoids reduced the formation of plaque-forming cells (i.e. Ig synthesis). These data imply that vitamin A present in human plasma is a normal modulator of B cell function.