Vitamin D3 down-regulates proinflammatory cytokine response to Mycobacterium tuberculosis through pattern recognition receptors while inducing protective cathelicidin production

Abstract

A well-known association between vitamin D3 and infection with Mycobacterium tuberculosis has previously been reported, but little is known regarding the underlying mechanisms. We have investigated how 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] affects the proinflammatory cytokine production induced by M. tuberculosis. Furthermore, we explored whether 1,25(OH)2D3 influence the production of the protective antimycobacterial peptide cathelicidin. Upon in vitro stimulation with M. tuberculosis, 1,25(OH)2D3 induced a dose-dependent down-regulation of IL-6, TNFα and IFNγ, while increasing the production of IL-10 in culture supernatant as well as cathelicidin mRNA expression. This effect on cytokine response was not due to modulation of T-helper cell differentiation, as T-bet, GATA3, Foxp3 and ROR-γt mRNA expression remained unaffected. Similarly, 1,25(OH)2D3 did not affect suppressor of cytokine signaling (SOCS)1 and SOCS3 mRNA expression. The mechanism whereby 1,25(OH)2D3 inhibited the proinflammatory cytokine response was through reduced expression of the pattern recognition receptors (PRR) – TLR2, TLR4, Dectin-1 and mannose receptor, whose mRNA and protein expression were both reduced. The suppression of PRRs could be restored by a VDR antagonist. Upon M. tuberculosis stimulation, 1,25(OH)2D3 modulates the balance in cytokine production towards an anti-inflammatory profile by repression of TLR2, TLR4, Dectin-1 and mannose receptor expression, while increasing cathelicidin production. These two effects may have beneficial consequences, by reducing the collateral tissue damage induced by proinflammatory cytokines, while the antibacterial effects of cathelicidin are enhanced.