Bacillary replication and macrophage necrosis are determinants of neutrophil recruitment in tuberculosis

Abstract

We previously determined that burst size necrosis is the chief mode of mononuclear cell death in the lungs of mice with tuberculosis. The present study explored the link between infection-induced necrosis of mononuclear phagocytes and neutrophil accumulation in the lungs of mice challenged with one of four Mycobacterium tuberculosis strains of increasing virulence (RvΔphoPR mutant, H37Ra, H37Rv and Erdman). At all time points studied, Erdman produced the highest bacterial load and the highest proportion and number of M. tuberculosis-infected neutrophils. These parameters, and the proportion of TUNEL-positive cells, tracked with virulence across all strains tested. Differences in neutrophil infection were not reflected by levels of chemoattractant cytokines in bronchoalveolar lavage fluid, while interferon-γ (reported to suppress neutrophil trafficking to the lung in tuberculosis) was highest in Erdman-infected mice. Treating Erdman-infected mice with ethambutol decreased the proportion of mononuclear phagocytes with high bacterial burden and the ratio of infected neutrophils to infected mononuclear cells in a dose-dependent manner. We propose that faster replicating M. tuberculosis strains cause more necrosis which in turn promotes neutrophil recruitment. Neutrophils infected with M. tuberculosis constitute a biomarker for poorly controlled bacterial replication, infection-induced mononuclear cell death, and increased severity of immune pathology in tuberculosis.

Impaired Recognition ofMycobacterium tuberculosisby Alveolar Macrophages From Diabetic Mice

“…The key signals that initiate an innate response to the presence of M. tuberculosis-infected AMs in the lung are not known with certainty. In the 2-week period after low-dose aerosol infection with M. tuberculosis Erdman, the lung bacterial load increases by 0.3-0.4 log per day [16]. A reduced rate of phagocytosis, followed by slower growth of intracellular bacilli to a burst-sized load in diabetic AMs, could delay the induction of innate immunity by several days.…”

“…Viability was no different in macrophages from normoglycemic or HG mice ( Figure 3D). We previously reported that the horizontal spread of M. tuberculosis infection from AMs to newly recruited macrophages, myeloid dendritic cells (mDCs), and neutrophils in the lung depends on intracellular bacterial replication to a threshold burden that triggers necrosis of the infected macrophage [15,16]. If M. tuberculosis grows more slowly in the AMs of diabetic hosts, this could delay immunostimulatory macrophage necrosis, transmission of bacilli to mDCs and neutrophils, and transfer of bacilli to lymph nodes for adaptive immune priming.…”

Pathology and immune reactivity: understanding multidimensionality in pulmonary tuberculosis

“…Frequencies of neutrophils in the blood of exposed individuals inversely correlate with risk of TB [81], suggesting a protective role of neutrophils. In murine models, kinetics of neutrophils in the alveolar space parallels in situ cell death of resident macrophages [82] and fine-tunes subsequent inflammatory responses [74,83,84]. The extent of alveolar macrophage death and early tissue damage modulates preadaptive neutrophilic infiltration of the alveolar space [74,82].…”

“…In murine models, kinetics of neutrophils in the alveolar space parallels in situ cell death of resident macrophages [82] and fine-tunes subsequent inflammatory responses [74,83,84]. The extent of alveolar macrophage death and early tissue damage modulates preadaptive neutrophilic infiltration of the alveolar space [74,82]. Signaling through IFN-alpha receptor-1 (IFNAR1) promotes bacillary replication and death of alveolar macrophages [74].…”

“…Neutrophils have been detected in granulomas in multiple animal models [66,133,135] and in human lesions already in the pre-antibiotic era [61]. Heightened accumulation of neutrophils [82,83], which express granzyme B [136], parallels Mtb numbers and causes intra-granulomatous necrosis [136]. Involvement of neutrophils in lung injury and TB transmission will be discussed in the context of cavity formation in the following.…”