Serine protease activity contributes to control of Mycobacterium tuberculosis in hypoxic lung granulomas in mice
Stephen T. Reece, Christoph Loddenkemper, David J. Askew, Ulrike Zedler, Sandra Schommer-Leitner, Maik Stein, Fayaz Ahmad Mir, Anca Dorhoi, Hans-Joachim Mollenkopf, Gary A. Silverman, Stefan H.E. Kaufmann
Stephen T. Reece, Christoph Loddenkemper, David J. Askew, Ulrike Zedler, Sandra Schommer-Leitner, Maik Stein, Fayaz Ahmad Mir, Anca Dorhoi, Hans-Joachim Mollenkopf, Gary A. Silverman, Stefan H.E. Kaufmann
View: Text | PDF
Research Article Infectious disease

Serine protease activity contributes to control of Mycobacterium tuberculosis in hypoxic lung granulomas in mice

Abstract

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.

Authors

Stephen T. Reece, Christoph Loddenkemper, David J. Askew, Ulrike Zedler, Sandra Schommer-Leitner, Maik Stein, Fayaz Ahmad Mir, Anca Dorhoi, Hans-Joachim Mollenkopf, Gary A. Silverman, Stefan H.E. Kaufmann

×

Figure 2

Blocking of TNF-α or IFN-γ leads to development of caseous necrosis within granulomas.

Options: View larger image (or click on image) Download as PowerPoint
Blocking of TNF-α or IFN-γ leads to development of caseous necrosis with...
(A) H&E staining of lung tissue at day 56 p.i. demonstrated the presence of nonnecrotizing (N) and caseous granulomas (C), after blocking of TNF-α or IFN-γ in Nos2–/– mice (original magnification, ×25). (B) Giemsa staining of caseous granulomas distinguished the central necrotic region from the cellular periphery (original magnification, ×200). Ziehl-Neelsen staining revealed presence of M. tuberculosis in both locations. Regions within the rectangles are shown at higher magnification (original magnification, ×1,000). (C) Number of granulomas per section in control mice and after blocking of TNF-α or IFN-γ. The entire left lobe was sectioned, H&E stained, and the total number of granulomas per section were enumerated per mouse (n = 5). Blocking of TNF-α or IFN-γ caused significantly increased numbers of granulomas per section and (D) significantly increased percentages of granulomas demonstrating caseous necrosis per section compared with control mice (mean ± SEM; n = 5). **P < 0.01; ***P < 0.001.