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Parasitic helminth worms, such as Schistosoma mansoni, are endemic in regions with a high prevalence of tuberculosis (TB) among the population. Human studies suggest that helminth coinfections contribute to increased TB susceptibility and increased rates of TB reactivation. Prevailing models suggest that T helper type 2 (Th2) responses induced by helminth infection impair Th1 immune responses and thereby limit Mycobacterium tuberculosis (Mtb) control. Using a pulmonary mouse model of Mtb infection, we demonstrated that S. mansoni coinfection or immunization with S. mansoni egg antigens can reversibly impair Mtb-specific T cell responses without affecting macrophage-mediated Mtb control. Instead, S. mansoni infection resulted in accumulation of high arginase-1-expressing macrophages in the lung, which formed type 2 granulomas and exacerbated inflammation in Mtb-infected mice. Treatment of coinfected animals with an antihelminthic improved Mtb-specific Th1 responses and reduced disease severity. In a genetically diverse mouse population infected with Mtb, enhanced arginase-1 activity was associated with increased lung inflammation. Moreover, in patients with pulmonary TB, lung damage correlated with increased serum activity of arginase-1, which was elevated in TB patients coinfected with helminths. Together, our data indicate that helminth coinfection induces arginase-1-expressing type 2 granulomas, thereby increasing inflammation and TB disease severity. These results also provide insight into the mechanisms by which helminth coinfections drive increased susceptibility, disease progression, and severity in TB.

The hallmark of human Mycobacterium tuberculosis infection is the presence of lung granulomas. Lung granulomas can have different phenotypes, with caseous necrosis and hypoxia present within these structures during active tuberculosis. Production of NO by the inducible host enzyme NOS2 is a key antimycobacterial defense mechanism that requires oxygen as a substrate; it is therefore likely to perform inefficiently in hypoxic regions of granulomas in which M. tuberculosis persists. Here we have used Nos2-/- mice to investigate host-protective mechanisms within hypoxic granulomas and identified a role for host serine proteases in hypoxic granulomas in determining outcome of disease. Nos2-/- mice reproduced human-like granulomas in the lung when infected with M. tuberculosis in the ear dermis. The granulomas were hypoxic and contained large amounts of the serine protease cathepsin G and clade B serine protease inhibitors (serpins). Extrinsic inhibition of serine protease activity in vivo resulted in distorted granuloma structure, extensive hypoxia, and increased bacterial growth in this model. These data suggest that serine protease activity acts as a protective mechanism within hypoxic regions of lung granulomas and present a potential new strategy for the treatment of tuberculosis.

Various arachidonic acid (AA) metabolites are known to regulate immune cell function(s) and dictate the progression of both acute and chronic inflammatory reactions. Using a model of Schistosoma mansoni egg-induced hypersensitivity granulomas, we have delineated the in vivo effects of inhibitors of cyclooxygenase (CO) and lipoxygenase (LO) pathways on granuloma development and granuloma macrophage I-region-associated (Ia) antigen expression. In addition, by high performance liquid chromatography (HPLC) we have profiled the metabolism of AA by macrophages that are isolated from granulomatous foci, and have biochemically characterized the in vitro specificity and activity of selected CO and LO inhibitors. The development of hypersensitivity-type pulmonary granulomas in mice was dramatically suppressed by inhibitors with anti-LO activity (nordihydroguairetic acid (NDGA), nafazatrom, and BW755c) in a dose-dependent manner, while indomethacin, which is primarily CO-selective, had no significant effect. Furthermore, NDGA and nafazatrom profoundly arrested the normal progression of preformed granulomatous lesions. The inhibitors of the LO pathway also suppressed the in vivo kinetics of Ia antigen expression by granuloma macrophages. In contrast, indomethacin augmented Ia-antigen expression. The major AA metabolites that were synthesized by the granuloma macrophages were shown to be leukotriene C4 and mono-hydroxyeicosatetraenoic acids. HPLC analysis of AA metabolites from granuloma macrophages that were treated with the various inhibitors confirmed that indomethacin was most CO-selective and NDGA most LO-selective. Nafazatrom and BW755c inhibited AA metabolism by both pathways. Notably, high concentrations of the compounds (5 X 10(-5) M) tended to suppress all products. Our results suggest that LO products may be important in the generation and maintenance of immune granulomatous inflammatory responses.

Lung lavage levels of angiotensin-converting enzyme (ACE)-like activity were increased in C57BL/6 mice with Bacille Calmette-Guérin (BCG)-induced chronic granulomatous pulmonary inflammation and splenomegaly. Contrariwise, ACE activity was not increased in lung lavage fluids of CBA mice that developed only minimal pulmonary inflammation in response to BCG. ACE-like activity correlated with the intensity of inflammation and Captopril, a specific competitive inhibitor of ACE activity, markedly suppressed the induction and maintenance of the BCG-induced inflammatory response in both lungs and spleen. It was necessary, however, to provide sustained treatment with large doses of Captopril in order to reduce the inflammatory response. After a single intraperitoneal injection of Captopril, ACE levels in lung lavage of BCG-injected mice were reduced but returned to preinjection levels or greater within 24 h. The highest dose of Captopril was more effective in reducing the lung fluid level of ACE in BCG-inflamed lungs. This suggests that sustained daily injections of Captopril were necessary to maintain reduced ACE levels. In vitro studies indicated that high concentrations of Captopril did not affect macrophage mobility or chemotactic activity for macrophages. Thus, ACE may act as a molecular mediator of BCG-induced granulomatous inflammation in the lung.

Angiotensin-converting enzyme (ACE) activity was measured in isolated peripheral blood monocytes and culture medium from 28 patients with sarcoidosis and compared with values obtained from monocytes of 25 normal control subjects. ACE activity was determined by radioimmunoassay of angiotensin II produced from angiotensin I. While there was no measurable ACE activity in monocytes or culture medium from normal controls under the conditions of our study, monocytes from patients with sarcoidosis all showed activity both in cells and culture medium. The mean ACE activity of monocytes from patients with sarcoidosis was 2.0 pg angiotensin II formed/min per 10(5) cells, and that released into medium over a 24-h interval was 30.4 pg angiotensin II/min per 10(5) cells. The monocyte ACE from patients with sarcoidosis was activated by chloride ions and inhibited by EDTA, captopril, and rabbit antiserum to purified human plasma ACE, indicating that enzymatic activity was effected specifically by ACE. Thus, our studies show a significant elevation and release of ACE by peripheral blood monocytes of patients with sarcoidosis under conditions where monocytes of normal control subjects do not demonstrate ACE activity.

Murine schistosomiasis is a granulomatous disease associated with high serum and granuloma angiotensin I-converting enzyme (ACE) activity. SQ 14225, a specific competitive inhibitor of ACE, was administered to normal mice and mice infected with Schistosoma mansoni to determine whether this compound could inhibit granuloma ACE activity and modify the size of the granulomatous response to schistosome eggs. Peroral administration of SQ 14225 for 5 wk to infected mice with peak granulomatous responses decreased ACE activity in isolated liver granulomas. Treated mice demonstrated a decrease in granuloma size in the liver, colon, and ileum, and hydroxyproline concentration of isolated liver granulomas was increased. Mean diameters of synchronous pulmonary granulomas, induced by the pulmonary embolization of schistosome eggs into normal and sensitized mice, were decreased by a similar dose of SQ 14225. Withdrawal of SQ 14225 from unsensitized mice with 2-wk-old synchronous pulmonary granulomas induced an increase in inflammation. Infected, but not normal mice receiving SQ 14225 demonstrated reduced portal pressure, liver weight, and body weight. Both normal and infected mice experienced dipsogenesis, expanded intravascular volume, and increased serum ACE. These observations suggest that SQ 14225 can partially inhibit the granulomatous response to schistosome eggs and the pathological manifestations of schistosomiasis. It is possible that ACE has an inflammatory role in granulomatous inflammation.