Mycobacteria infect different cell types in the human lung and cause species dependent cellular changes in infected cells

Abstract

BackgroundMycobacterial infections remain a significant cause of morbidity and mortality worldwide. Due to limitations of the currently available model systems, there are still comparably large gaps in the knowledge about the pathogenesis of these chronic inflammatory diseases in particular with regard to the human host. Therefore, we aimed to characterize the initial phase of mycobacterial infections utilizing a human ex vivo lung tissue culture model designated STST (Short-Term Stimulation of Tissues).MethodsHuman lung tissues from 65 donors with a size of 0.5–1 cm3 were infected each with two strains of three different mycobacterial species (M. tuberculosis, M. avium, and M. abscessus), respectively. In order to preserve both morphology and nucleic acids, the HOPE® fixation technique was used. The infected tissues were analyzed using histo- and molecular-pathological methods. Immunohistochemistry was applied to identify the infected cell types.ResultsMorphologic comparisons between ex vivo incubated and non-incubated lung specimens revealed no noticeable differences. Viability of ex vivo stimulated tissues demonstrated by TUNEL-assay was acceptable. Serial sections verified sufficient diffusion of the infectious agents deep into the tissues. Infection was confirmed by Ziel Neelsen-staining and PCR to detect mycobacterial DNA. We observed the infection of different cell types, including macrophages, neutrophils, monocytes, and pneumocytes-II, which were critically dependent on the mycobacterial species used. Furthermore, different forms of nuclear alterations (karyopyknosis, karyorrhexis, karyolysis) resulting in cell death were detected in the infected cells, again with characteristic species-dependent differences.ConclusionWe show the application of a human ex vivo tissue culture model for mycobacterial infections. The immediate primary infection of a set of different cell types and the characteristic morphologic changes observed in these infected human tissues significantly adds to the current understanding of the initial phase of human pulmonary tuberculosis. Further studies are ongoing to elucidate the molecular mechanisms involved in the early onset of mycobacterial infections in the human lung.

Mycobacterium abscessus-Induced Granuloma Formation Is Strictly Dependent on TNF Signaling and Neutrophil Trafficking

“…Our results are distinct from those with Mycobacterium tuberculosis or M . marinum where neutrophils appear to be less mobilized [34,38]. Ex vivo infections of human lung tissues indicated that neutrophils had a greater tendency to phagocytize Mabs than M .…”

“…Ex vivo infections of human lung tissues indicated that neutrophils had a greater tendency to phagocytize Mabs than M . tuberculosis and that Mabs has a higher capacity to induce the migration of neutrophils than other mycobacterial species [38]. Additionally, while neutrophils are unable to kill virulent strains of M .…”

In vitro and ex vivo systems at the forefront of infection modeling and drug discovery

“…The first method (Fig. 4A) begins with surface decontamination, followed by dissection of tissues into cubes of approximately equal sizes [59,239]. In pigs, surface decontamination could be carried out by briefly searing the ventral surface of the pleura (< 1s) with a hot pallet knife [239].…”

“…Similar techniques are also applicable to lung tissues from human donors. In a recent study, a human ex vivo lung tissue culture model was used to characterize the initial phase of mycobacterial infections and it was discovered that the infection of different cell types in early mycobacterial infections is bacteria species dependent [59]. Unfortunately, the ex vivo lung model prepared following this procedure also has limitations, the most important of which is the high variance in the data obtained, which most likely resulted from tissue heterogeneity and inconsistent cutting.…”

Modeling tuberculosis pathogenesis through ex vivo lung tissue infection

“…In a report of ex vivo human lung tissue infected with M. tuberculosis, M. avium and M. abscessus, Ganbat et al [32], found macrophages, neutrophils, monocytes, and pneumocytes-II infected with mycobacteria and nuclear alterations resulting in cell death depending on the mycobacterial species used. This system provides a similarity to the original lung microenvironment with its native cell population, orientation, and structural integrity.…”