The Role of Single Nucleotide Polymorphisms in C-Type Lectin Receptors and the Signaling Molecules in their Pathways in Susceptibility towards developing Pulmonary Tuberculosis in an Indian Population

Tuberculosis (TB) is a multifactorial disease being affected by bacterial, host as well as environmental factors. Mycobacterium tuberculosis (Mtb) engages a number of receptors during infection and the pathogenesis not only depends upon the receptors involved but all the adaptors down the signaling pathways and their cross-talk and involvement with other receptors/pathways. The members of C-type lectin receptors (CTLRs) have recently been described as important in TB pathogenesis. Some of these receptors can directly recognize the potent virulence factors of Mtb cell wall and induce several pro-inflammatory immune responses. Not many studies have been performed looking into the genetic variations among these receptors and their effects of TB disease. In this study, important CTLRs and their signaling molecules involved in TB infection and pathogenesis were investigated for potential TB associated single nucleotide polymorphisms (SNPs). We performed a case-control study consisting of 144 HIV-negative new pulmonary TB cases and 181 healthy controls recruited in Hyderabad, India, and the DNA was collected from the blood of each subject. A two stage sequencing approach was adopted in which candidate common variations were first screened out in a pilot explorative phase by Ampliseq based next generation sequencing consisting of 80 samples. An adjustment for population stratification was performed assuming a heterogeneous population and the candidate SNPs were genotyped and verified in all the samples in the validation phase. The results showed no association of SNPs in CTLRs with the occurrence of (pulmonary TB) PTB. However, while also focusing on signaling proteins related to CTLRs we found that SNP rs3774275 in MASP1, which is downstream of the MBL pathway, is significantly associated with pulmonary TB (PTB) in our population (meta- analysis p=0.034). The G allele occurs more frequently among controls and seems to provide a protective effect against TB in this study population. Furthermore, the MASP-1 and Map44 serum levels are significantly higher in TB patients when compared to healthy controls. A further in vitro experiment with recombinant human MASP-1 (rhMASP-1) demonstrated that addition of MASP-1 in serum increases the lectin pathway activity, suggesting a functional role of MASP-1 in TB pathogenesis. In conclusion, this study demonstrates a significant relationship between MASP-1 polymorphisms and serum levels and development of pulmonary TB, suggesting an important role of lectin pathway in TB pathogenesis. Moreover, the results propose MASP-1 as a potential genetic marker for TB resistance