Cathelicidin augments VDR-dependent anti-leishmanial immune response in Indian Post-Kala-Azar Dermal Leishmaniasis

Objectives: Indian Post kala-azar dermal leishmaniasis (PKDL) is the cutaneous aftermath of visceral leishmaniasis (VL) caused by L. donovani. Vitamin D-regulated cationic antimicrobial peptide cathelicidin (hCAP-18/LL37) has microbicidal and immunomodulatory role against cutaneous infections, but its role in PKDL remains elusive. Methods: Skin snips and blood-derived monocytes of PKDL patients (n = 46), before (B1) and after (AT) chemotherapy, were used for this study. Serum vitamin D3 level was evaluated by ELISA. Cathelicidin and vitamin D receptor (VDR) levels were analyzed by real-time PCR and flowcytometry in PKDL patients. The mechanistic effect of cathelicidin on macrophage differentiation and anti-leishmanial activity was assessed through RNA interference techniques followed by subsequent microscopic evaluation of in vitro parasite killing and Thl/Th2 counter-regulation by ELISA/RT-PCR. Results: Low vitamin D3 levels were accompanied with decreased expression of cathelicidin and VDR in PKDLBT patients. Results suggested positive induction of VDR-dependent cathelicidin in PKDL macrophages by Amphotericin B treatment, which could be due to indirect effect of drug-induced IL12 upregulation. 1,25 Vitamin D3 stimulation induced cathelicidin in PKDL-BT patients through involvement of TLR2/IL-1 beta, but not TLR4. Cathelicidin also augmented the and-leishmanial effect and macrophage activating potential of Amphotericin B, attributable to regulation of VDR-dependent enhancement of CD40, p-STAT-I and MHC-II expression leading to regulation of IL10/IL12 balance in PKDL-BT patient macrophages. Conclusions: This study indicates that cathelicidin augments anti-leishmanial macrophage activating property of Amphotericin B in a TLR2/VDR dependent mechanism, and advocate the development of novel adjunct treatment modality of cathelicidin with conventional Amphotericin B in PKDL patients.