Early innate immunity determines outcome of Mycobacterium tuberculosis pulmonary infection in rabbits

Abstract

BackgroundPulmonary infection of humans by Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), results in active disease in 5-10% of individuals, while asymptomatic latent Mtb infection (LTBI) is established in the remainder. The host immune responses that determine this differential outcome following Mtb infection are not fully understood. Using a rabbit model of pulmonary TB, we have shown that infection with the Mtb clinical isolate HN878 (a hyper-virulent W-Beijing lineage strain) leads to progressive cavitary disease similar to what is seen in humans with active TB. In contrast, infection with Mtb CDC1551 (a hyper-immunogenic clinical isolate) is efficiently controlled in rabbit lungs, with establishment of LTBI, which can be reactivated upon treatment with immune-suppressive drugs. We hypothesize that the initial interaction of Mtb with the cells of the host response in the lungs determine later outcome of infection.ResultsTo test this hypothesis, we used our rabbit model of pulmonary TB and infected the animals with Mtb HN878 or CDC1551. At 3 hours, with similar lung bacillary loads, HN878 infection caused greater accumulation of mononuclear and polymorphonuclear leukocytes (PMN) in the lungs, compared to animals infected with CDC1551. Using whole-genome microarray gene expression analysis, we delineated the early transcriptional changes in the lungs of HN878- or CDC1551-infected rabbits at this time and compared them to the differential response at 4 weeks of Mtb-infection. Our gene network and pathway analysis showed that the most significantly differentially expressed genes involved in the host response to HN878, compared to CDC1551, at 3 hours of infection, were components of the inflammatory response and STAT1 activation, recruitment and activation of macrophages, PMN, and fMLP (N-formyl-Methionyl-Leucyl-Phenylalanine)-stimulation. At 4 weeks, the CDC1551 bacillary load was significantly lower and the granulomatous response reduced compared to HN878 infection. Moreover, although inflammation was dampened in both Mtb infections at 4 weeks, the majority of the differentially expressed gene networks were similar to those seen at 3 hours.ConclusionsWe propose that differential regulation of the inflammation-associated innate immune response and related gene expression changes seen at 3 hours determine the long term outcome of Mtb infection in rabbit lungs.

Pathology and immune reactivity: understanding multidimensionality in pulmonary tuberculosis

“…Neutrophil abundance in the lung alveoli immediately following Mtb implantation directly correlates with virulence of the Mtb strains employed [80]. Frequencies of neutrophils in the blood of exposed individuals inversely correlate with risk of TB [81], suggesting a protective role of neutrophils.…”

Innate Resistance to Tuberculosis in Man, Cattle and Laboratory Animal Models: Nipping Disease in the Bud?

“…Prior to the onset of acquired immunity, the lungs of experimentallyinfected susceptible rabbits contained 20-to 30-fold more Mtb organisms than those of resistant rabbits (Dannenberg and Rook, 1994) and a more recent study in rabbits suggested that the ultimate outcome of pulmonary Mtb infection is significantly influenced by the differential regulation of the innate immune response and associated gene expression as early as 3 h post infection (Subbian et al, 2013). Variation in these innate responses may reflect the antibacterial effectiveness of myriad components within the host immune armoury such as pathogen recognition by cell receptors, phagocytosis and the production of intra-and extracellular immunomodulatory compounds including cytokines.…”

Cryptococcus inositol utilization modulates the host protective immune response during brain infection

“…The log2-transformed transcript levels from uninfected, wild type-infected or mutant-infected mice brain (n = 3 per group) was further analyzed by Partek Genomics Suite (Partek, St.Louis, MO) for statistical analysis and to identify significantly differentially expressed genes (SDEG) in the infected group, relative to the uninfected animals. The normalized RNA-Seq data from each group (n = 3) were averaged and analyzed by one-way ANOVA with equal variance for significance [48]. To identify SDEG, the log2 ratio between uninfected and wild type-or the mutantinfected transcript levels was further screened by applying an unadjusted false discovery rate (FDR) of 5% (q value ≤ 0.05).…”

“…Gene ontology analysis was performed by interrogating the SDEG generated in our studies with the IPA knowledgebase as described [48]. To improve the stringency, we included only mouse database from IPA for the network/pathway analysis.…”