Chlamydia pneumoniae activates IKK/IkB-mediated signaling, which is inhibited by 4-HNE and following primary exposure Bernadette Donath a,1 , Claudia Fischer a,1 , Sharon Page a , Sigrid Prebeck b , Nikolaus Jilg a , Marion Weber a , Clarissa da Costa b , Dieter Neumeier a , Thomas Miethke b , Korbinian Brand a, * a Institute of Clinical Chemistry and Pathobiochemistry, Technische Universita ¨t Mu ¨nchen, Klinikum rechts der Isar, Ismaninger Strasse 22, 81675 Mu ¨nchen, Germany b Institute of Medical Microbiology, Technische Universita ¨t Mu ¨nchen, Mu ¨nchen, Germany Received 10 December 2001; received in revised form 1 May 2002; accepted 17 May 2002 Abstract Chlamydia pneumoniae may be involved in atherosclerosis by inducing inflammation as well as LDL oxidation. The transcription factor NF-kB is found in an active state in atherosclerotic lesions. This study examined the effect of C. pneumoniae exposure on the NF-kB system in human monocytic lineage cells. Short exposure to C. pneumoniae as well as chlamydial heat shock protein 60 activated NF-kB, accompanied by increased cytokine production. Incubation with C. pneumoniae induced depletion of IkB-a and later IkB-o which was preceded by IkB kinase complex activation. 4-Hydroxynonenal, an aldehyde LDL oxidation product, was shown to inhibit C. pneumoniae induced NF-kB activation by preventing IkB phosphorylation/proteolysis. During long-term incubation with C. pneumoniae IkB-a returned to baseline, whereas the levels of IkB-o and p65 were upregulated. Interestingly, long- term preincubation with C. pneumoniae selectively prevented restimulation by this microorganism, which appears to be at least partly facilitated by inhibition of IkB proteolysis. C. pneumoniae -induced NF-kB activation as well as the inhibition of that effect under certain conditions may contribute to chronic inflammation with potential relevance to vascular disease. # 2002 Published by Elsevier Science Ireland Ltd. Keywords: Chlamydia pneumoniae ; NF-kB; 4-Hydroxynonenal; Monocyte/macrophage; Atherosclerosis 1. Introduction The presence of the respiratory pathogen Chlamydia pneumoniae in atherosclerotic lesions suggests involve- ment of this microorganism in inflammatory processes observed during atherosclerosis [1  /3]. C. pneumoniae has been shown to multiply in monocyte/macrophages as well as endothelial and smooth muscle cells, primarily involved in atherogenesis [3]. Furthermore, C. pneumo- niae infection may induce chronic inflammation mediated by cyto- and chemokines as well as thrombotic events [1,3,4]. Transgenic animal experiments indicate that C. pneumoniae works synergistically with other risk factors, such as high cholesterol, to accelerate the atherosclerotic process [1,3]. C. pneumoniae has also been shown to induce cellular LDL oxidation and foam cell formation [5,6]. These processes may impair a proper immune response of cells to bacteria in the atherosclerotic lesion [5  /8]. Following extensive LDL oxidation a variety of products arises like the aldehyde 4-hydroxynonenal (HNE) [9  /12]. Numer- ous HNE effects in different cell types have been described and HNE-modified lysine residues have been identified in the lesion [7,9]. The transcription factor NF-kB plays an important role in inflammatory, immune and proliferative pro- cesses and is activated in atherosclerotic lesions, e.g. in monocytic cells [13  /15]. NF-kB comprises dimers, commonly p50/p65, that are trapped in the cytosol by inhibitory proteins, including IkB-a and -o [16,17]. Numerous molecules or conditions modulate NF-kB, * Corresponding author. Tel.:  /49-89-4140-4084; fax:  /49-89- 4140-4080 E-mail address: brand@klinchem.med.tu-muenchen.de (K. Brand). 1 Sharing first authorship. Atherosclerosis 165 (2002) 79  /88 www.elsevier.com/locate/atherosclerosis 0021-9150/02/$ - see front matter # 2002 Published by Elsevier Science Ireland Ltd. PII:S0021-9150(02)00198-3