SummaryChlamydia pneumoniae causes respiratory infections. In chronic diseases associated with Chlamydia , such as arteriosclerosis, C. pneumoniae is present in a persistent form, which might participate in pathogenesis of chronic inflammatory disease. To elucidate how these intracellular bacteria modulate host-cells during persistence, we compared the expression pattern of a range of host genes after short (24 h) and long (up to 7 days) times of chlamydia infection in HeLa-cells. One day post infection, in three cellculture models of persistence, namely treatment with penicillin or IFN-g g g g , or iron-depletion, infection induced the genes of CTGF, IL-6, IL-8, IL-11, LIF, EGR-1 and ETV4 in a similar fashion. However, after a longer time, two modes of host-cell reaction emerged that were dependent on the persistence model used. After IFN-g g g g and penicillin treatment chlamydia-induced host-cell gene expression was inhibited, while it stayed upregulated in iron-depletion. Human monocytes/macrophages, in which persistence naturally occurs, were additionally investigated: for several genes, UV-inactivated and viable chlamydia caused long-lasting upregulation. Thus, this study reveals (i) the ability of C. pneumoniae to participate in two putative pathomechanisms of persistence, silencing and permanent activation, which might represent different in vivo situations and (ii) a strong dependence on the mode of persistence induction.

The anaphylatoxic peptide C3a is a pro‐inflammatory mediator generated during complement activation, whose specific G protein coupled receptor is expressed on granulocytes, monocytes, mast cells, activated lymphocytes, and in the nervous tissue. We have generated RBL‐2H3 cell clones stably expressing mutants of the human C3a‐receptor (C3aR) with combined alanine (Ala) substitutions of ten C‐terminal serine (Ser) or threonine (Thr) residues, which may represent putative phosphorylation sites to characterize their role in ligand‐induced C3aR internalization and signaling. Ser475/479 and Thr480/481 as well as Ser449 seemed not to be involved in ligand‐induced receptor internalization. Either directly or by a conformational change they even "inhibit" C3aR internalization. In contrast, mutants with Ala substitutions at Ser465/470 and Thr463/466 were poorly internalized, and Thr463 seemed to be the most important C‐terminal Thr or Ser residue directly effecting receptor internalization. However, it is likely that other C3aR regions additionally participate in this negative feed‐back mechanism since even mutants with multiple Ala substitutions still internalized to a limited degree. Interestingly, in a mutant with a single exchange of Ser449 to Ala, the signal transduction assessed by a Ca2+ assay and [35S]GTPγS‐binding on HEK cells transiently co‐transfected with G‐alpha 16 or G‐alpha O, respectively, was severely impaired, indicating that this residue of C3aR is involved in G protein coupling.

The anaphylatoxin C3a is a proinflammatory mediator generated during complement activation. The tight control of C3a receptor (C3aR) expression is crucial for the regulation of anaphylatoxinmediated effects. Key factors regulating constitutive expression of the C3aR in the mast cell line HMC-1 and receptor induction by dibutyryl-cAMP in monomyeloblastic U937 cells were determined by functional characterization of the C3aR promoter. Nucleotides ؊18 to ؊285 upstream of the translational start site proved to be critical for promoter activity in HMC-1 cells. Binding sites for the transcription factors AP-1 and Ets could be located. Overexpressed c-Jun/c-Fos (AP-1) and Ets-1 led synergistically to increased promoter activity that was substantially reduced by site-directed mutagenesis of the corresponding elements within the C3aR promoter. In HMC-1 cells, Ets interacted directly with the predicted binding motif of the C3aR promoter as determined by electromobility shift assays. AP-1 binding to the C3aR promoter was augmented during C3aR induction in U937 cells. A retroviral gene transfer system was used to express a dominant negative mutant of Ets-1 in these cells. The resulting cells failed to up-regulate the C3aR after stimulation with dibutyryl-cAMP and showed decreased AP-1 binding, suggesting that Ets acts here indirectly. Thus, it was established that Ets and the AP-1 element mediates dibutyrylcAMP induction of C3aR promoter activity, hence providing a mechanistic explanation of dibutyryl-cAMP-dependent up-regulation of C3aR expression. In conclusion, this study demonstrates an important role of AP-1 and a member of the Ets family in the transcriptional regulation of C3aR expression, a prerequisite for the ability of C3a to participate in immunomodulation and inflammation.The complement system is activated in a variety of diseases (1-3) and leads to the generation of the anaphylatoxic peptide C3a.2 This proinflammatory mediator binds specifically to its heptahelical receptor (C3aR) (4, 5) which is expressed on various cells such as leukocytes, endothelial and broncho-epithelial cells, smooth muscle cells of the lung, and even neurons (4, 6, 7).The best experimental evidence for the involvement of C3a in diseases has been obtained in animal models using C3aR knock-out mice, guinea pigs with a natural C3aR defect, or specific C3aR inhibitors (8 -12). Intriguingly, C3a and its receptor act partially protective, partially destructive. In endotoxin shock, C3a seems to be protective; the mortality rate of C3aR Ϫ/Ϫ mice was much higher than that of their wild type littermates, investigated by a cecal ligation puncture sepsis model (12). Moreover, C3a participates in liver regeneration after partial hepatectomy or toxic injury (13,14).As demonstrated in an adjuvant-induced arthritis rat model, C3a aggravates the inflammatory reaction (8). In asthma, C3a is deleterious because C3aRϪ/Ϫ -mice are protected from ovalbumin-driven airway hyper-responsiveness and early phase bronchoconstriction (15). In man C3a might play a si...

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