Functionally Overlapping Variants Control Tuberculosis Susceptibility in Collaborative Cross Mice

Abstract

<jats:title>ABSTRACT</jats:title> <jats:p>Host genetics plays an important role in determining the outcome of <jats:named-content content-type="genus-species">Mycobacterium tuberculosis</jats:named-content> infection. We previously found that Collaborative Cross (CC) mouse strains differ in their susceptibility to <jats:named-content content-type="genus-species">M. tuberculosis</jats:named-content> and that the CC042/GeniUnc (CC042) strain suffered from a rapidly progressive disease and failed to produce the protective cytokine gamma interferon (IFN-γ) in the lung. Here, we used parallel genetic and immunological approaches to investigate the basis of CC042 mouse susceptibility. Using a population derived from a CC001/Unc (CC001) × CC042 intercross, we mapped four quantitative trait loci (QTL) underlying tuberculosis immunophenotypes (<jats:italic>Tip1</jats:italic> to <jats:italic>Tip4</jats:italic>). These included QTL that were associated with bacterial burden, IFN-γ production following infection, and an IFN-γ-independent mechanism of bacterial control. Further immunological characterization revealed that CC042 animals recruited relatively few antigen-specific T cells to the lung and that these T cells failed to express the integrin alpha L (αL; i.e., CD11a), which contributes to T cell activation and migration. These defects could be explained by a CC042 private variant in the <jats:italic>Itgal</jats:italic> gene, which encodes CD11a and is found within the <jats:italic>Tip2</jats:italic> interval. This 15-bp deletion leads to aberrant mRNA splicing and is predicted to result in a truncated protein product. The <jats:italic>Itgal<jats:sup>CC042</jats:sup></jats:italic> genotype was associated with all measured disease traits, indicating that this variant is a major determinant of susceptibility in CC042 mice. The combined effect of functionally distinct <jats:italic>Tip</jats:italic> variants likely explains the profound susceptibility of CC042 mice and highlights the multigenic nature of tuberculosis control in the Collaborative Cross.</jats:p> <jats:p><jats:bold>IMPORTANCE</jats:bold> The variable outcome of <jats:named-content content-type="genus-species">Mycobacterium tuberculosis</jats:named-content> infection observed in natural populations is difficult to model in genetically homogeneous small-animal models. The newly developed Collaborative Cross (CC) represents a reproducible panel of genetically diverse mice that display a broad range of phenotypic responses to infection. We explored the genetic basis of this variation, focusing on a CC line that is highly susceptible to <jats:named-content content-type="genus-species">M. tuberculosis</jats:named-content> infection. This study identified multiple quantitative trait loci associated with bacterial control and cytokine production, including one that is caused by a novel loss-of-function mutation in the <jats:italic>Itgal</jats:italic> gene, which is necessary for T cell recruitment to the infected lung. These studies verify the multigenic control of mycobacterial disease in the CC panel, identify genetic loci controlling diverse aspects of pathogenesis, and highlight the utility of the CC resource.</jats:p>