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Immunogenetic and Gene Expression Analyses of Mycobacterium tuberculosis Infection in Mice
Summary: Dr. Apt is analyzing immunogenetic and gene expressionn of certain bacterium in mice.
I/St and A/Sn mice display a severe and a mild course of tuberculosis (TB), respectively. TB response in the lungs of I/St mice is characterized by 1) prominent inflammation, 2) a decrease in type 1cytokines, 3) impaired antimycobacterial macrophage function, and 4) marked proliferation of T lymphocytes. The multiplicity of phenotypes correspond well to a polygenic pattern of TB control previously mapped to loci on chromosomes 3, 9, 17, and X, loci that regulate disease severity. Recently, we demonstrated a striking feature of TB response in the lungs of I/St mice: prolonged and severe infiltration with neutrophils. Compared with neutrophils of A/Sn, those of I/St more readily migrated and phagocytosed mycobacteria in an opsonin-dependent manner in in vitro transwell and in vivo peritoneal inflammatory models. Given that tissue neutrophils showed negligible mycobacteriostatic capacity, we speculate that in TB-susceptible animals neutrophils play the role of a “Trojan horse," hiding mycobacteria from the host immune system and serving as an important element of pathogenesis.
Using mRNA from I/St and A/Sn lung macrophages applied to Affymetrix array U74Av2, gene expression studies indicated that infection results in iNOS, hsp70, IL-10Ra, Csf-2, and Mmp10 up-regulation, but in Mmp8 down-regulation. Importantly, the expression of IL-11 and IL-6 genes was 12-fold and 3-fold higher, respectively, in both naive and infected I/St lung macrophages, compared with their A/Sn counterparts. We confirmed these data by RT-PCR and Taqman PCR analyses. We assume that the genetically determined high level of pro-inflammatory non–T cell cytokines in the lung is another feature of TB pathogenesis. We continued to develop congenic mouse strains that differ in those segments of Chr. 3 and 9 that are involved in TB control. In the Chr. 3 set, genotyping of the BC4–BC6 progeny allowed us to select mice in which the linkage peak marker D3Mit215 was separated by crossing over from the left flanking marker D3Mit29 and the right flanking marker D3Mit199.
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