Persistent Inactivation of Macrophage Cyclooxygenase-2 in Mycobacterial Pulmonary Inflammation

Abstract

The induction of cyclooxygenase-2 (COX-2) in tissue macrophages (MØ) increases prostaglandin E 2 (PGE 2 ) release, potentially downregulating granulomatous inflammation. In response to Mycobacteria, local MØ express COX-2, which is either nuclear envelope (NE)-associated or NE-dissociated. Persistent mycobacterial pulmonary inflammation is characterized by alveolar MØ expressing NEdissociated (inactive) COX-2 without release of PGE 2 . In this study, we examined COX-2 in alveolar MØ after intranasal exposure to heat-killed Mycobacterium bovis BCG (HK-BCG). After administration, whole lungs of C57Bl/6 mice were lavaged with saline; COX-2 expression and PGE 2 release by alveolar MØ and tumor necrosis factor (TNF)-a and nitric oxide levels in the lung lavage were monitored. Normal alveolar MØ had undetectable levels of COX-2 on Western blots. However, 1 day after intranasal administration, almost all alveolar MØ had phagocytosed HK-BCG and expressed NE-dissociated COX-2 without any increase in the release of PGE 2 . At 28 days after intranasal administration, 68% of alveolar MØ still contained both BCG and the NE-dissociated form of COX-2. NEassociated (active) COX-2 was not observed in alveolar MØ. In contrast, 7 days after intraperitoneal injection of HK-BCG, peritoneal MØ containing HK-BCG were no longer detected. At 28 days after intranasal administration, TNF-a and nitrite levels in the lung lavage fluid were significantly higher than those in controls. Our results indicate that mycobacterial pulmonary inflammation is associated with suppressed PGE 2 production by alveolar MØ, with expression of COX-2 dissociated from the NE.

Cholera Toxin Induces a Shift from Inactive to Active Cyclooxygenase 2 in Alveolar Macrophages Activated by Mycobacterium bovis BCG

“…vaccination of mice with Mycobacterium bovis bacillus Calmette-Guérin (BCG) offered better protection against M. tuberculosis than did systemic vaccination (12). Our previous studies (13,14) indicate that alveolar M, activated by i.n. heatkilled BCG, develop bactericidal M (M1) that facilitate Th1 immunity.…”

“…However, in these M1 M, both COX-1 and COX-2 are dissociated from the nuclear envelop (NE), accumulate in aggregates in the endoplasmic reticulum (ER), and are catalytically inactive. Although PGE synthase, which converts PGH 2 to PGE 2 , appears to be active (15), these COX-2 ϩ M release no PGE 2 (13). Furthermore, the impairment of PGE 2 release seems to be independent of degradation of PGE 2 driven by 15-hydroxyprostaglandin dehydrogenase (16).…”

“…Intranasal Mycobacterium tuberculosis, Mycobacterium butyricum, and Propionibacterium acnes, like BCG, also induce M1 activation of alveolar M that is characterized by the inactive forms of COX-2 and COX-1 (13). In contrast, i.n.…”

“…In contrast, i.n. administration of heatkilled Escherichia coli or lipopolysaccharide (LPS) induces NEassociated COX-2, which can be inactivated by subsequent in vivo stimulation by BCG, suggesting that selected microbes regulate whether alveolar M express active or inactive COX-2 (13). Mycobacterial inactivation of COX will limit PGE 2 -mediated mucosal protection and immune responses.…”

“…Mycobacterial inactivation of COX will limit PGE 2 -mediated mucosal protection and immune responses. Therefore, it would be important to understand the mechanism(s) regulating inactive/ NE-dissociated COX formation in response to mucosal mycobacterial vaccination in vivo and NE-associated, active COX-2 in murine alveolar M (or other tissue M) cultured with BCG in vitro (13,17,18).…”