Analysis of the local kinetics and localization of interleukin‐1α, tumour necrosis‘qc factor‐α and transforming growth factor‐β, during the course of experimental pulmonary tuberculosis

Abstract

SUMMARYA mouse model of pulmonary tuberculosis induced by the intratracheal instillation of live and virulent mycobacteria strain H37-Rv was used to examine the relationship of the histopathological findings with the local kinetics production and cellular distribution of tumour necrosis factor-a (TNF-a), interleukin-1a (IL-1a) and transforming growth factor-b ( TGF-b). The histopathological and immunological studies showed two phases of the disease: acute or early and chronic or advanced. The acute phase was characterized by inflammatory infiltrate in the alveolar-capillary interstitium, blood vessels and bronchial wall with formation of granulomas. During this acute phase, which lasted from 1 to 28 days, high percentages of TNF-a and IL-1a immunostained activated macrophages were observed principally in the interstium-intralveolar inflammatory infiltrate and in granulomas. Electron microscopy studies of these cells, showed extensive rough endoplasmic reticulum, numerous lysosomes and occasional mycobacteria. Double labelling with colloid gold showed that TNF-a and IL-1a were present in the same cells, but were confined to separate vacuoles near the Golgi area, and mixed in larger vacuoles near to cell membrane. The concentration of TNF-a and IL-1a as well as their respective mRNAs were elevated in the early phase, particularly at day 3 when the bacillary count decreased. A second peak was seen at days 14 and 21-28 when granulomas appeared and evolved to full maturation. In contrast, TGF-b production and numbers of immunoreactive cells were low in comparison with the advanced phase of the disease. The chronic phase was characterized by histopathological changes indicative of more severity (i.e. pneumonia, focal necrosis and extensive interstitial fibrosis) with a decrease in the TNF-a and IL-1a production that coincided with the highest level of TGF-b. The bacillary counts were highest as the macrophages became large, vacuolated foamy cells, and containing numerous bacilli with immunoreactivity to mycobacterial lipids and lipoarabinomannan ( LAM). These macrophages displayed poor and scarce TNF-a and IL-1a immunostaining but still strong immunoreactivity to TGF-b. These cytokine production kinetics and the spatial relationship between immunostained cells and lung lesions corroborate the important role of TNF-a and IL1a in the constitution of granulomas and immune protection during the early phase of the infection, and also suggest an important if not primary role for TGF-b in the immunopathogenesis of the advanced forms of pulmonary tuberculosis.

Macrophage and T lymphocyte apoptosis during experimental pulmonary tuberculosis: their relationship to mycobacterial virulence

“…NO is an efficient mycobactericidal factor in murine macrophages, and it is also an effective inducer of apoptosis [7]. The observation that animals infected with the hypervirulent Beijing strain had lower expression of IFN-c, TNF-a, and iNOS, permitting higher bacillary growth [14,18], is in agreement with the reduced apoptosis of macrophage demonstrated in the present work. It is possible that reduced apoptosis of macrophages contributes to increase bacillary survival.…”

“…In these pneumonic areas, small groups of activated macrophages were seen, but large macrophages with vacuolated cytoplasm were very common, and these were studied separately. We previously noted that these vacuolated macrophages (VM) only exist during the progressive phase of the infection [14]. Interestingly, relatively few of these VM were apoptotic at day 21 post infection in mice infected with the H37Rv strain (16.6%), and at day 60, the percentage was even lower (8.7%) ( Fig.…”

“…When mice are infected with H37Rv, there is rapid and strong production of TNF-a by activated macrophages, accompanied by progressively increasing expression of IFN-c and inducible NO synthase (iNOS) peaking at 3 weeks. This response temporarily controls bacterial growth [14,18]. The disease then enters a progressive phase with continuing bacterial proliferation, rising expression of IL-4, IL-10, and TGF-b, and falling expression of TNF-a, IFN-c and iNOS [13,14].…”

“…This response temporarily controls bacterial growth [14,18]. The disease then enters a progressive phase with continuing bacterial proliferation, rising expression of IL-4, IL-10, and TGF-b, and falling expression of TNF-a, IFN-c and iNOS [13,14]. Using this experimental model, we recently published the observation that in comparison with H37Rv, three different Beijing strains were hypervirulent, and induced rapid death with massive pneumonia, very high CFU counts and lower expression of TNF-a, iNOS, and IFN-c [15].…”

“…Here we describe the kinetics of macrophage and T lymphocyte apoptosis in vivo during the course of experimental pulmonary tuberculosis, using a wellcharacterized model in BALB/c mice infected by intratracheal injection with a high dose of live and virulent M. tuberculosis strain H37Rv [13,14]. We used the terminal d-UTP nucleotide end labeling (TUNEL) technique to determine the percentage of apoptotic macrophages in lung sections throughout the infection, and immunohistochemistry to estimate the percentage of Bcl-2-, Bax-, FasL-, and Fas-immunostained macrophages.…”