Joint Effects of Host Genetic Background and Mycobacterial Pathogen on Susceptibility to Infection

Abstract

The present study examined the differential contribution of host genetic background and mycobacterial pathogen variability to biological and mechanistic phenotypes of infection. For this purpose, A/J and C57BL/6J mice were infected intravenously with a low dose of Mycobacterium tuberculosis H37Rv or the Russia, Japan, and Pasteur substrains of Mycobacterium bovis bacille Calmette-Guérin (BCG). The pulmonary bacterial counts (number of CFU) and transcript levels of select cytokines (e.g., Ifng, Il12b, and Il4) at 1, 3, and 6 weeks postinfection were measured as biological and mechanistic phenotypes, respectively. The individual and combined impact of the host and mycobacteria on these phenotypes was assessed using three-way analysis of variance (ANOVA), which partitions phenotypic variation into host, pathogen, time, and interaction effects. All phenotypes, except pulmonary Il4 transcript levels, displayed evidence for host-mycobacterium specificity by means of significant interaction terms. Pulmonary expression profiles of 34 chemokines and chemokine-related genes were compared across the hosts and mycobacteria. The differences in induction of these immune messenger genes between A/J and C57BL/6J mice were modest and generally failed to reach significance. In contrast, the mycobacteria induced significant variance in a subset of the immune messenger genes, which was more evident in A/J mice relative to that in C57BL/6J mice. Overall, the results demonstrated the importance of considering the joint effects of the mycobacterial and host genetic backgrounds on susceptibility to mycobacterial infections.Exposure of humans to Mycobacterium tuberculosis, the cause of tuberculosis, induces a highly variable response. Among persons exposed to M. tuberculosis, only 30 to 50% become infected during an outbreak, and of those infected, only approximately 10% develop clinical disease. There is now clear evidence for the important impact of host genetic factors on this variable response (3,11,12). Evidence for an equally important role of M. tuberculosis strain variability is emerging (reviewed in references 18 and 35). A univariate view would suggest that those who develop disease either display low resistance to M. tuberculosis or are infected with high-virulence strains of M. tuberculosis. An alternate multivariate view is that M. tuberculosis and its human hosts have coevolved such that host susceptibility and pathogen virulence might better be considered in combination. A specific M. tuberculosis isolate may cause disease in certain hosts but not in others, while a specific host may be susceptible to certain M. tuberculosis isolates but resistant to others. The extent to which multivariate interactions are decisive for tuberculosis susceptibility has far-reaching consequences for tuberculosis control efforts, including vaccine development. Although studies have examined the impact of host background and mycobacterial type separately, strategies that focus on the simultaneous analysis of host and mycobacteria in disease e...

Comparative genomic analysis of Mycobacterium tuberculosis clinical isolates

“…The relatively high number of SNPs we identified in all isolates could be partially caused by natural variation, as we included all genes from 7 strains isolated from patients diversely located. Selective diversification of M. tuberculosis isolates might also explain an association between host response and strain genetic background as previously reported [12, 13]. Several lines of evidence in this study support a significant role of natural selection in shaping M. tuberculosis genomes.…”

After the bottleneck: Genome-wide diversification of the Mycobacterium tuberculosis complex by mutation, recombination, and natural selection

“…First, the SNP distribution in genomes is not random, suggesting that diversifying selection is at work notably in genes playing a role in cell wall/membrane/envelope biogenesis, which tend to accumulate an excess of SNPs. This result is probably related to the lifestyle of the tubercle bacilli, producing long chronic colonization of hosts, which might result in selection pressure for arms races with the host, e.g., to evade host defenses (Dawkins and Krebs 1979) or diversifying selection to adapt to different host genetic backgrounds (Di Pietrantonio et al 2011). While we still lack examples of horizontal gene transfer after the last common ancestor of MTBC, our approach was not aimed at identifying regions that could not be mapped in extant genomes; rather, we showed that regions transferred to the ancestor of MTBC also accumulate an excess of SNPs.…”

Correlates between Models of Virulence for Mycobacterium tuberculosis among Isolates of the Central Asian Lineage: a Case for Lysozyme Resistance Testing?

“…tuberculosis isolates found in epidemiologically defined clusters are defined as successful because they transmit and cause TB in more human hosts, in the same population, than the case for other isolates. It is also a generally accepted idea that overall strain success depends on a combination of strain virulence traits and host genetic factors (8,14,16,62,63). The contribution of mycobacterial VFs to establishing disease (TB) or causing pathogenicity, however, was recently reemphasized (42,64); as VFs are likely to be lineage specific (23-25, 38, 43), their existence might have far-reaching impacts on the efficacy of new TB vaccines or drugs (65).…”