Genetics of host innate immune factors in Tuberculosis susceptibility

Tuberculosis, caused by Mycobacterium tuberculosis, is globally a leading cause of morbidity and mortality. While a host genetic contribution to tuberculosis susceptibility is known to occur, the extent and nature of host genetic variability to tuberculosis pathogenesis are unknown. Thus, to better understand the role of host genetic factors in tuberculosis susceptibility, we have tested the contribution of candidate gene variants to tuberculosis susceptibility in three geographically, epidemically, and clinically distinct populations. We chose four candidate genes involved in the innate immune response, namely, NRAMP1, MBL, SFTPA1, and SFTPA2.Since the global spread of tuberculosis is highly dependent on HIV/AIDS pandemic, we investigated the association of genetic MBL variants and HIV-1 infection in 278 Colombian HIV-infected and control individuals. MBL genotype frequencies were similar for both groups, and no association was detected between MBL alleles B, C, and D and susceptibility to HIV-1 infection (P = 1.0). These results do not support the hypothesis that MBL levels are a risk factor for HIV-1 infection in Colombia. Moreover, we were able to show that MBL variants do not contribute to tuberculosis susceptibility in this population.In a pediatric population composed of 184 families we found allelic variants in the NRAMP1 gene to be associated with tuberculosis disease (P = 0.01; Odds ratio [OR] = 1.75 [95% confidence interval: 1.10--2.77]). Common NRAMP1 alleles were identified as risk factors for pediatric tuberculosis while these same alleles were reported to be protective in adult cases, suggesting that the common alleles promote rapid progression from infection to tuberculosis disease. Furthermore, the association of NRAMP1 with pediatric tuberculosis disease was significantly heterogeneous (P = 0.01) between simplex (P < 0.0008; OR = 3.13 [1.54--6.25]) and multiplex families (P = 1) suggesting an interplay between mechanisms of genetic control and exposure intensities. Finally, we tested the correlation between the NRAMP1 risk and NRAMP1 functional activity by measuring the recruitment efficiency of mannose-6-phosphate receptor (M6PR) to Salmonella containing vacuoles (SCV) in monocyte-derived-macrophages (MDM). We show that recruitment of M6PR to SCV is significantly lower ( P = 0.024) in MDM from patients homozygous for the risk allele as compared to MDM from heterozygous patients. Thus, altered function of NRAMP1 appears to modulate the rate of progression from infection to disease