ABSTRACT
A mouse model of pulmonary tuberculosis induced by the intratracheal instillation of live and virulent mycobacteria strain H37-Rv was used to study the relationship of the histopathological changes with the kinetics of local production and circulating levels of interleukin 6 (IL-6) and the gene expression of acute phase proteins (APP) in the liver. The histopathological studies showed a mononuclear inflammatory infiltrate located in the perivascular, peribronchial, and interstitial areas, with granulomas which started to form 2 weeks after the infection. Numerous IL-6 immunostained activated macrophages were observed in the inflammatory infiltrate, particularly in the interstitial-intralveolar compartment and granulomas, coexisting with a high IL-6 mRNA concentration determined by reverse transcription polimerase chain reaction in lung homogenates, particularly at day 21 of infection. Two peaks of IL-6 demonstrated by ELISA in lung homogenates and sera were observed at day 3 and 21 of infection, being higher on the latter. The hepatic APP mRNA transcription (alpha1-acid glycoprotein, fibrinogen, complement factor 4) analyzed by Northern blot showed a rapid and high increase at day one postinfection, which rapidly decreased and showed another second peak at day 21, when granulomas reached full maturity and the maximal production of IL-6 was observed. At the same time the liver mRNA concentrations of the negative APP albumin showed a substantial decrease. From 1 to 4 months after M. tuberculosis intratracheal instillation, histopathological changes of more severity (pneumonia, necrosis) and chronicity (interstitial fibrosis) were seen, as well as small groups of IL-6 immunostained macrophages in the pneumonic areas, granulomas and perivascular compartments, in coexistence with low IL-6 expression. During this advanced stage of the disease a high mRNA concentration of alpha1-acid glycoprotein and fibrinogen associated with low expression of the albumin gene in the liver continued. Thus, it seems that the time course of hepatic APP genetic expression in experimental pulmonary tuberculosis is related to the production of IL-6 and relevant histopathological changes, particularly the formation of granuloma.
