Bronchoalveolar Lavage and Plasma Cathelicidin Response to 25-Hydroxy Vitamin D Supplementation: A Pilot Study

Reduced vitamin D-induced cathelicidin production and killing of Mycobacterium tuberculosis in macrophages from a patient with a non-functional vitamin D receptor: A case report

Tuberculosis (TB) presents a serious health problem with approximately a quarter of the world’s population infected with Mycobacterium tuberculosis (M. tuberculosis) in an asymptomatic latent state of which 5–10% develops active TB at some point in their lives. The antimicrobial protein cathelicidin has broad antimicrobial activity towards viruses and bacteria including M. tuberculosis. Vitamin D increases the expression of cathelicidin in many cell types including macrophages, and it has been suggested that the vitamin D-mediated antimicrobial activity against M. tuberculosis is dependent on the induction of cathelicidin. However, unraveling the immunoregulatory effects of vitamin D in humans is hampered by the lack of suitable experimental models. We have previously described a family in which members suffer from hereditary vitamin D-resistant rickets (HVDRR). The family carry a mutation in the DNA-binding domain of the vitamin D receptor (VDR). This mutation leads to a non-functional VDR, meaning that vitamin D cannot exert its effect in family members homozygous for the mutation. Studies of HVDRR patients open unique possibilities to gain insight in the immunoregulatory roles of vitamin D in humans. Here we describe the impaired ability of macrophages to produce cathelicidin in a HVDRR patient, who in her adolescence suffered from extrapulmonary TB. The present case is a rare experiment of nature, which illustrates the importance of vitamin D in the pathophysiology of combating M. tuberculosis.

25-Hydroxyvitamin D potentializes extracellular cathelicidin release from human PBMC stimulated ex vivo with either bacterial (LPS) or viral (P: IC) mimetics

Human cathelicidin refers to the cationic antimicrobial peptide hCAP18/LL-37. LL-37 is formed by cleavage of the propeptide hCAP18 coded by the CAMP gene. The active form of vitamin D, 1,25-dihydroxyvitamin D (1,25(OH)D), has been shown to induce the CAMP gene expression through promoter activation. We previously failed to demonstrate in a clinical trial that supplementation of 25-hydroxyvitamin D (25(OH)D) improves LL-37 serum levels. The aim of this work was to evaluate the impact of 25(OH)D supplementation on intracellular expression of CAMP and secretion of LL-37 in an ex vivo model using the peripheral blood mononuclear cells (PBMC). PBMC collected from healthy donors and incubated with different concentrations of 25(OH)D (0 ng/ml: control (D0); 25 ng/ml: deficient (D25); 75 ng/ml: physiological (D75); 125 ng/ml: supraphysiological (D125)) were stimulated or not with lipopolysaccharide (LPS, 100 ng/ml) or synthetic double-stranded RNA Poly (I: C) (PIC, 10 µg/ml). The intracellular expressions of the CAMP gene and the hCAP18 peptide were measured respectively after 24-h and 48-h incubation periods. The concentration of LL-37 was determined in the culture medium after 48-h incubation. 25(OH)D significantly induced CAMP gene expression at 24 h with a maximum effect at a dose of D125 in either unstimulated (tenfold expression) or stimulated (LPS: 100-fold expression; PIC: 15-fold expression) conditions. Intracellular hCAP18 peptide was overexpressed at 48 h under unstimulated (1.5-fold, D125) and stimulated conditions, LPS (twofold, D125) and PIC (2.5-fold, D125). The secretion of LL-37 in the culture medium was significantly induced by 25(OH)D only in both stimulated (LPS and PIC) conditions in a dose-dependent manner. Our results demonstrate that 25(OH)D incubation increases intracellular expression of CAMP and hCAP18, but extracellular secretion of LL-37 antimicrobial peptide is increased by 25(OH)D only when PBMC from healthy donors were stimulated with bacterial or viral immune mimetic.