IFN-γ- and TNF-Independent Vitamin D-Inducible Human Suppression of Mycobacteria: The Role of Cathelicidin LL-37

Abstract

Vitamin D deficiency is associated with susceptibility to tuberculosis, and its biologically active metabolite, 1α,25 dihydroxyvitamin D3 (1α,25(OH)2D3), has pleiotropic immune effects. The mechanisms by which 1α,25(OH)2D3 protects against tuberculosis are incompletely understood. 1α,25(OH)2D3 reduced the growth of mycobacteria in infected human PBMC cultures in a dose-dependent fashion. Coculture with agonists or antagonists of the membrane or nuclear vitamin D receptors indicated that these effects were primarily mediated by the nuclear vitamin D receptors. 1α,25(OH)2D3 reduced transcription and secretion of protective IFN-γ, IL-12p40, and TNF in infected PBMC and macrophages, indicating that 1α,25(OH)2D3 does not mediate protection via these cytokines. Although NOS2A was up-regulated by 1α,25(OH)2D3, inhibition of NO formation marginally affected the suppressive effect of 1α,25(OH)2D3 on bacillus Calmette Guérin in infected cells. By contrast, 1α,25(OH)2D3 strongly up-regulated the cathelicidin hCAP-18 gene, and some hCAP-18 polypeptide colocalized with CD14 in 1α,25(OH)2D3 stimulated PBMC, although no detectable LL-37 peptide was found in supernatants from similar 1α,25(OH)2D3-stimulated PBMC cultures. A total of 200 μg/ml of the active peptide LL-37, in turn, reduced the growth of Mycobacterium tuberculosis in culture by 75.7%. These findings suggest that vitamin D contributes to protection against TB by “nonclassical” mechanisms that include the induction of antimicrobial peptides.

Supplemental vitamin D increases serum cytokines in those with initially low 25-hydroxyvitamin D: A randomized, double blind, placebo-controlled study

“…Data presented as mean (SD). [31,33], serum 25(OH)D before inversely correlated with the change in serum 25(OH)D concentrations after supplemental vitamin D. The changes in 25(OH)D also correlated with those of 1,25(OH)D, suggesting that a disruption in the metabolite used to define vitamin D status associates with a disturbance in the hormonal form of vitamin D, and that those with low serum 25(OH)D before display the greatest increase in serum 25(OH)D and 1,25(OH)D after supplemental vitamin D. Since low vitamin D increases pro-inflammatory cytokines [34,35] and vitamin D treatment (i.e., with 25(OH)D or 1,25(OH)D) inhibits pro-inflammatory and promotes anti-inflammatory cytokine production in cell culture [34][35][36][37][38], we speculated that a greater increase in serum 25(OH)D and 1,25(OH)D with supplemental vitamin D in those with initially low vitamin D levels would associate with a decrease in pro-inflammatory and an increase in antiinflammatory cytokines. Following stratification to initial vitamin D levels, supplemental vitamin D increased IFN-c and IL-10 in those with an insufficient compared to a sufficient serum 25(OH)D concentration at baseline.…”

Vitamin D and Calcium Abnormalities in the HIV-Infected Population

“…[104][105][106] In the general population, persons with 25-OHD less than 4 ng/mL were shown to have 3-fold odds of having active tuberculosis. 107 Vitamin D has also been historically used to treat pulmonary tuberculosis during the preantibiotic era with mixed results.…”

Vitamin D and Innate Immunity

“…Although epithelial cells at the interface between the outside and inside environment of the host express antimicrobial peptides [72], it is the innate immune cells at that external-internal barrier, such as neutrophils [73], mast cells [74], and monocytes/macrophages [51,75], that are recognized to be the major producers of antimicrobial peptides. Several antimicrobial peptides produced by macrophages have been demonstrated to have direct antimicrobial activity against M. tuberculosis, including but most likely not limited to LL-37 (cathelicidin) [12,76], hBD2 (DEFB4) [77], and hepcidin [78]. In humans, cathelicidin and DEFB4 were found to contain activating VDREs in their promoter regions; whether or not hepcidin is vitamin D-regulated at the level of transcription is unknown [50].…”

“…In humans, cathelicidin and DEFB4 were found to contain activating VDREs in their promoter regions; whether or not hepcidin is vitamin D-regulated at the level of transcription is unknown [50]. Activation of the VDR in monocytes/macrophages results in the expression of cathelicidin at both the mRNA and protein levels [12,50,76]. siRNA knockdown of 1,25D-induced cathelicidin in human monocytic cells resulted in complete loss of antimicrobial activity [52], suggesting that antimicrobial peptides represent a major human macrophage host defense mechanism.…”