| dc.description.abstract | Background: The human antimicrobial peptide cathelicidin (LL-37) is involved in host innate immunity by the after activation of Toll-like receptors (TLRs), resulting in direct killing of Mycobacterium tuberculosis (MTB). We hypothesized that LL-37 could be a potential biomarker for the diagnosis of tuberculosis (TB) infection and disease due to its direct antimicrobial killing properties that destroy the bacterial cell wall. We further hypothesized that bioavailable vitamin D levels are a better indicator of vitamin D status than total vitamin D levels and that LL-37 expression is mediated by vitamin D-binding polymorphisms protein (VDBP/DBP) gene and free and bioavailable vitamin D levels. Tuberculin skin test (TST) and QuantiFERON-TB Gold In-Tube (QFT), have been used for diagnosis of latent TB infection (LTBI) but have limitations of differentiating it from the active (ATB) state. This study aimed to evaluate the influence of the DBP gene polymorphisms and vitamin D bioavailabilty on LL-37 expression as a potential biomarker of TB infection and disease differentiation.
Methods: After ethical approval a comparative cross-sectional study with 148 participants, including 56 patients with ATB, 49 with LTBI, and 43 with no TB infection. Samples from household contacts with LTBI and individuals with no TB infection from the Kampala TB Cohort (KTB), previously stored, were collected for analysis. Free and bioavailable vitamin D and LL-37 levels were measured using (abx570015) 25-Hydroxyvitamin D3 (Calcidiol) ELISA kits and (abx150919) Human Cathelicidin Antimicrobial Peptide (CAMP) ELISA kits, respectively. Genotyping of the DBP rs4588 and rs7041 was performed by Polymerase Chain Reaction (PCR) and Sanger sequencing. Receiver operating characteristic curve (ROC) analysis using area under the curve (AUC) was performed to determine the discriminating ability of LL-37 in LTBI and ATB disease. Statistical analysis was performed with STATA software version 12.0
Results: LL-37 levels were higher among ATB patients and lowest among those without TB infection (p=0.002). The ATB patients had the lowest levels of free and bioavailable vitamin D, 1.3 (1.10, 1.80) ng/mL compared to LTBI, 4.2 (2.50, 6.20) ng/mL, and subjects without TB infection 5.3 (3.20, 6.20) ng/mL, p<0.001. Free and bioavailable with total vitamin D levels were comparable of the groups, 17.0 ng/mL, 22.9 ng/mL and 21.7 ng/mL, respectively Gc1F genotype was 97%, Gc2 genotype was 2% and the Gc1S genotype 1%, with Hardy-Weinberg equilibrium (D1 = 0, r2 = 0.015). The median vitamin D levels in the predominant genotype Gc1F were 3.8 ng/mL, in Gc1S 2.2 ng/mL, and Gc2 1.9 ng/mL. Logistic regression analysis between DBP polymorphism and free and bioavailable vitamin D levels showed no statistically significant association (p=0.52). Spearman's correlation analysis between DBP gene polymorphism and free vitamin D revealed a negative association (r-0.0404), p=0.6. A significant nonlinear relationship was observed between the two fractions of free vitamin D with LL-37 levels.
Conclusion: From the systematic review, we concluded that active pulmonary TB disease is associated with hypovitaminosis D and elevated circulating LL-37 levels, and low local LL-37 expression. A high proportion of hypovitaminosis D and significantly low free and bioavailable vitamin D levels were associated with the active TB state. The Gc1F genotype was predorminantly found, in the population with a non-significant association between the DBP and free and bioavailable vitamin D levels observed. Additionally elevated LL-37 levels were expressed in the active TB state. Therefore, LL-37 was able to discriminate between ATB and other TB infection states, particularly with the no TB infection.
Main recommendations: Further evaluation of LL-37 as a screening biomarker to rule out TB is needed. Therefore, other studies aimed at assessing the relationship between free and bioavailable levels, the downstream molecule 1,25-hydroxyvitamin D with LL-37, may be informative. Studies of DBP genetic polymorphisms and free and bioavailable vitamin D levels should be considered in a heterogeneous population to detect minor alleles. This study can guide the healthy policy of using vitamin D in preventive or definitive treatment of TB. | en_US |
