Exploring Host-driven Immunopathological Factors Developing Severe Tuberculosis: Insights from Comparative Mouse...

Tuberculosis (TB) pathogenesis arises from complex interactions between host immune responses and the genetic diversity of Mycobacterium tuberculosis (Mtb). To elucidate host determinants of TB immunopathology, we conducted a comparative analysis of inbred mouse strains infected with the highly virulent Mtb K strain. Among the strains tested, C3H/HeJ and A/J mice exhibited markedly increased susceptibility, characterized by elevated pulmonary bacterial burdens and extensive necrotizing lung pathology. Interestingly, at 2 weeks post-infection (PI), both strains showed lower bacterial burdens, limited dissemination, and less pulmonary inflammation than C57BL/6 mice, but at 4 weeks PI, this trend reversed. The increased disease severity was closely associated with pronounced pulmonary neutrophilic infiltration, elevated systemic levels of granulocyte colony-stimulating factor (G-CSF), expansion of Lin⁻Sca-1⁻c-Kit⁺CD34⁺CD16/32⁺ granulocyte-monocyte progenitors (GMPs) in the bone marrow (BM), and a substantially increased pulmonary neutrophil-to-T cell (N/T) ratio, which positively correlated with disease progression. Depletion of neutrophils or blockade of type I IFN from 2 weeks PI significantly ameliorated disease severity, as evidenced by reduced bacterial burden, improved lung pathology, and normalization of the N/T ratio. Notably, IL-10 receptor blockade and aging specifically mitigated disease severity in A/J mice, whereas BCG vaccination conferred greater protection in C3H/HeJ mice. These strain-specific protective effects were consistently associated with restored N/T ratios, normalized GMP levels, and attenuated systemic G-CSF levels. Together, our findings identify the pulmonary N/T ratio and GMP expansion as central, mechanistically linked drivers of type I IFN signaling and neutrophil-mediated TB immunopathology.