In situ localization of TNFa/b, TACE and TNF receptors TNF-R1 and TNF-R2 in control and LPS-treated lung tissue M. Ermert a , C. Pantazis a , H.-R. Duncker b , F. Grimminger c , W. Seeger c , L. Ermert a, * a Department of Pathology, Justus-Liebig University Giessen, Langhansstr. 10, 35385 Giessen, Germany b Institute of Anatomy and Cell Biology, Justus-Liebig University Giessen, 35385 Giessen, Germany c Department of Internal Medicine, Justus-Liebig University Giessen, 35385 Giessen, Germany Received 23 July 2002; received in revised form 3 April 2003; accepted 8 April 2003 Abstract Tumor necrosis factor (TNF) has been implicated in several infectious and inflammatory lung diseases. Two closely related variants, TNFa and TNFb, elicit various cellular responses via two distinct TNF receptors, the 55-kDa TNF-R1 and the 75-kDa TNF-R2. Recently, a TNFa-converting enzyme (TACE) was described, which cleaves and releases the membrane-bound TNFa. In the present study in normal rat and human lung tissue, the constitutive expression of TNFa/b, TACE and TNF-R1/R2 was investigated by immunohistochemical techniques. In addition, TNFa and TNFb mRNA were localized by in situ hybridization. Both TNFa and TNFb were detected in various lung cell types. Expression of TNFa was particularly prominent in bronchial epithelial cells and vascular smooth muscle cells, next to alveolar macrophages. Both in situ hybridization for TNFa message and TACE immunostaining matched this expression profile. TNFb—so far only known to be produced by lymphocytes—was demonstrated in alveolar macrophages, bronchial epithelial cells, vascular smooth muscle cells and endothelial cells at the protein and the message level. Both TNF receptors were detected, with TNF-R1 being prominent on bronchial epithelial cells and endothelial cells, and TNF-R2 being expressed by nearly all cell types. Following LPS stimulation in isolated rat lungs TNFa/b signal intensity was largely reduced due to liberation of stored TNFa/b, while TACE immunoreactivity remained unchanged or was enhanced, demonstrating increased TNF generation. We conclude that both TNFa and TNFb are constitutively expressed by several non-leukocytic cell types in the human and rat lung. In concert with the expression of TACE and the TNF receptors R1 and R2, this finding suggests in addition to the known role of the TNF system in inflammation physiological functions of the TNF system in different compartments of the adult lung, with the vasculature and the bronchial tissue being of particular interest in addition to the leukocyte/macrophage populations. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: Immunohistochemistry; In situ hybridization; TNFa-converting enzyme; Vasotone regulation; Homeostasis; Lung physiology; Cytokines 1. Introduction Tumor necrosis factor (TNF) has been implicated in many inflammatory diseases, and is assumed to be an important mediator in the sequel of sepsis and septic organ failure. There are two closely related proteins termed TNFa (cachectin) and TNFb (lymphotoxin), which possess similar yet not completely identical efficacy profiles. TNFa is involved in the initiation of cell death and may trigger a cascade of secondary proin- flammatory cytokines, e.g. in response to endotoxic challenge [1–3]. Recently, a metalloproteinase with TNFa precursor converting activity (TACE) has been characterized, which processes the membrane-bound www.elsevier.com/locate/jnlabr/ycyto Cytokine 22 (2003) 89–100 * Corresponding author. Fax: +49-6441-212253. E-mail address: leander.ermert@anatomie.med.uni-giessen.de (L. Ermert). 1043-4666/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1043-4666(03)00117-0