Genetic and functional evaluation of the role of DLL1 in susceptibility to visceral leishmaniasis in India

Abstract

Chromosome 6q26–27 is linked to susceptibility to visceral leishmaniasis (VL) in Brazil and Sudan. DLL1 encoding the Delta-like 1 ligand for Notch 3 was implicated as the etiological gene. DLL1 belongs to the family of Notch ligands known to selectively drive antigen-specific CD4 T helper 1 cell responses, which are important in protective immune response in leishmaniasis. Here we provide further genetic and functional evidence that supports a role for DLL1 in a well-powered population-based study centred in the largest global focus of VL in India. Twenty-one single nucleotide polymorphisms (SNPs) at PHF10/C6orf70/DLL1/FAM120B/PSMB1/TBP were genotyped in 941 cases and 992 controls. Logistic regression analysis under an additive model showed association between VL and variants at DLL1 and FAM120B, with top associations (rs9460106, OR=1.17, 95%CI 1.01–1.35, P=0.033; rs2103816, OR=1.16, 95%CI 1.01–1.34, P=0.039) robust to analysis using caste as a covariate to take account of population substructure. Haplotype analysis taking population substructure into account identified a common 2-SNP risk haplotype (frequency 0.43; P=0.028) at FAM120B, while the most significant protective haplotype (frequency 0.18; P=0.007) was a 5-SNP haplotype across the interval 5’ of both DLL1 (negative strand) and FAM120B (positive strand) and extending to intron 4 of DLL1. Quantitative RT/PCR was used to compare expression of 6q27 genes in paired pre- and post-treatment splenic aspirates from VL patients (N=19). DLL1 was the only gene to show differential expression that was higher (P<0.0001) in pre- compared to post-treatment samples, suggesting that regulation of gene expression was important in disease pathogenesis. This well-powered genetic and functional study in an Indian population provides evidence supporting DLL1 as the etiological gene contributing to susceptibility to VL at Chromosome 6q27, confirming the potential for polymorphism at DLL1 to act as a genetic risk factor across the epidemiological divides of geography and parasite species.

Resistance to visceral leishmaniasis is severely compromised in mice deficient of bradykinin B2-receptors

“…Anti-parasite immune response against the parasite is still present at early infection and recovery after cure subsequent to chemotherapy; this can easily been assessed by the determination of the delayed type hypersensitivity following injection of a leishmanial antigen [3-5]. The variable degrees of susceptibility or natural resistance to VL have been the focus of intense studies in the mice and dog models [6,7] and in humans [8] since the 70’s. A genetic basis for the susceptibility to VL was described in mice, dogs and humans [7,9-11].…”

Mannose-binding Lectin (MBL) as a susceptible host factor influencing Indian Visceral Leishmaniasis

“…[30]. Geographical heterogeneity and host genetic variations in HLA-DRB1, HLA-DQA1, HLA class II region, SLC11A1 and DLL1 were shown to modulate VL susceptibility in Indian patients [31][32][33].…”

Determinants for the Development of Visceral Leishmaniasis Disease

“…In particular, NRAMP1 plays a key role in susceptibility to visceral disease [39]. A number of cytokines, chemokines, and their receptors (TNFα [40]; IL4 [41]; TGFβ [42]; IL2 receptor [43]; CXCR2 [44]), as well as mannan-binding lectin [45] and the Delta-like 1 ligand for Notch 3 (DLL1) [46], have also been associated with symptomatic versus asymptomatic disease. However, it is largely unknown how deeply polymorphisms in these host immune response genes penetrate to cause visceral leishmaniasis in the human population of endemic regions.…”