Presence of multiple lesion types with vastly different microenvironments in C3HeB/FeJ mice following aerosol infection with Mycobacterium tuberculosis

Abstract

Cost-effective animal models that accurately reflect the pathological progression of pulmonary tuberculosis are needed to screen and evaluate novel tuberculosis drugs and drug regimens. Pulmonary disease in humans is characterized by a number of heterogeneous lesion types that reflect differences in cellular composition and organization, extent of encapsulation, and degree of caseous necrosis. C3HeB/FeJ mice have been increasingly used to model tuberculosis infection because they produce hypoxic, well-defined granulomas exhibiting caseous necrosis following aerosol infection with Mycobacterium tuberculosis. A comprehensive histopathological analysis revealed that C3HeB/FeJ mice develop three morphologically distinct lesion types in the lung that differ with respect to cellular composition, degree of immunopathology and control of bacterial replication. Mice displaying predominantly the fulminant necrotizing alveolitis lesion type had significantly higher pulmonary bacterial loads and displayed rapid and severe immunopathology characterized by increased mortality, highlighting the pathological role of an uncontrolled granulocytic response in the lung. Using a highly sensitive novel fluorescent acid-fast stain, we were able to visualize the spatial distribution and location of bacteria within each lesion type. Animal models that better reflect the heterogeneity of lesion types found in humans will permit more realistic modeling of drug penetration into solid caseous necrotic lesions and drug efficacy testing against metabolically distinct bacterial subpopulations. A more thorough understanding of the pathological progression of disease in C3HeB/FeJ mice could facilitate modulation of the immune response to produce the desired pathology, increasing the utility of this animal model.

Spectinamides are effective partner agents for the treatment of tuberculosis in multiple mouse infection models

“…Here, roughly 60% of the infected mice became moribund between days 28 and 45 post-aerosol exposure due to TB infection and were humanely euthanized prior to the start of treatment. Histological examination of lung tissue from six untreated control mice that had survived this early mortality phase to day 56 post-aerosol exposure (start of treatment) revealed the presence of the three characteristic lung lesion types (not shown) 6 . At this time bacterial loads in the lungs of additional untreated mice had reached 9.09 log 10 cfu.…”

“…Early mortality in a subset (roughly 20%–40%) of infected, but untreated, C3HeB/FeJ mice is a hallmark of productive infection in this model 6 . Here, roughly 60% of the infected mice became moribund between days 28 and 45 post-aerosol exposure due to TB infection and were humanely euthanized prior to the start of treatment.…”

“…Treatment was initiated on day 56 at the time when necrotic lesions had already developed 6 and continued for 4 weeks. Groups of four or seven mice were sacrificed on day 56, prior to treatment initiation, and 3 days following the last day of treatment to determine the bacterial loads in the lungs of mice.…”

“…Building from these studies, herein we investigated the efficacy of 1599 in combination with conventional anti-TB agents, including agents under late-stage clinical development. Synergistic interactions were assessed by conventional in vitro chequerboard assays and also through a series of short-term (≤4 weeks) acute and chronic murine infection models of TB, including C3HeB/FeJ mice exhibiting advanced, hypoxic, caseating granulomas 5 , 6 . The resulting data revealed appreciable in vivo synergy between lead spectinamides and existing therapeutics, as well as compounds in late-stage clinical development that were not otherwise predicted by in vitro MIC chequerboard testing.…”

Sterilizing Activity of Pyrazinamide in Combination with First-Line Drugs in a C3HeB/FeJ Mouse Model of Tuberculosis

“…The C3HeB/FeJ mouse has attracted attention recently as a promising murine model because the mice develop caseous necrosis, and even cavities, that other commonly used murine models do not (6,7). Unlike the nonnecrotic cellular lung lesions found in commonly used mouse strains, like BALB/c, in which the vast majority of infecting bacilli are found intracellularly, C3HeB/FeJ mice harbor abundant extracellular bacilli in the caseous center of necrotic lesions and intracellular bacilli in nonnecrotic lesions and the cellular cuff surrounding necrotic lesions (8,9). In mice developing large liquefying caseous lung lesions, the bacterial burden is typically at least an order of magnitude higher, and the vast majority of the bacilli are extracellular.…”