Projects, methods, selected publications, and grants
- Cross talk between these intracellular bacteria and their host cells
- Chlamydial virulence factors
- Interaction of chlamydia with the complement system
Chlamydiae are obligate intracellular bacteria with a unique biphasic (virus-like) productive cycle. Depending on species and serovar chlamydia can cause a variety of diseases. Different serovars of Chlamydia trachomatis are responsible for eye infections (conjunctivitis and trachoma causing blindness), urogenital infections (STD) leading to infertility or ectopic pregnancy, and respiratory tract infections in newborns. Moreover, persistent C. trachomatis can cause reactive arthritis. Chlamydia pneumoniae is a frequent cause of usually mild respiratory infections and is also associated with other diseases such as vascular disorders. Chlamydia psittaci is an important pathogen in birds and other animals. Following transmission from avian sources, it can cause psittacosis in humans, a life-threatening atypical pneumonia with systemic spread. Infections of cattle, sheep, horses and other domestic animals with non-avian strains of C. psittaci can result in abortion, respiratory disorders, enteritis and arthritis.
Chlamydia express a type III secretion system. Bacteria use this system to transfer bacterial effector proteins into the host cells thereby "re-programming" them on the level of signal transduction or gene-expression and permitting bacterial infection and survival.
Our research group is mainly interested in the cross-talk between the obligate intracellular chlamydia and their host cells, the identification and characterization of chlamydial effector proteins (such as CT166 acting as virulence factor on the host cell cytoskeleton), and the understanding of chlamydial persistence. During the last years we also became interested in the elucidation of the role of the complement in infections caused by intracellular bacteria. In an ongoing investigation using a lung infection model with several knock-out mice we could show that effector functions downstream of complement factor C3 have a severe impact on the outcome of C. psittaci and C. pneumonia infection. We hope that our investigations will lead to a better understanding of the molecular pathomechanisms during chlamydial infections, and that they may contribute to the identification of new therapeutic targets.
2. THE COMPLEMENT SYSTEM
- Expression, regulation, and function of C5a-receptor, C3a-receptor, and C5L2
- Interaction of intracellular bacteria with the complement system
The complex and highly regulated complement system is central to immune effector functions against microorganisms. It consists of more than thirty different proteins, most of which are found in serum and other body fluids. Receptors for complement components and complement regulators are expressed on the host cell surface. Immune complexes, surface components of bacteria and yeast, C-reactive protein, mitochondria and necrotic cells trigger complement activation pathways. During activation, early and central mediators of the inflammatory cascade are generated by cleavage of complement factors, in particular the anaphylatoxic peptides C3a, C5a and its derivative C5adesArg.
The anaphylatoxins modulate the intensity of innate and adaptive specific immune responses. They act as mediators via related G protein coupled receptors, the C3a receptor and the C5a receptor. Their function is modulated by C5a receptor like 2 (C5L2), which is heptahelical but non-coupling to G proteins. C5L2 seems to serve mainly as a scavenger receptor for C5a and C5adesArg, competing with the biologically active C5a-receptor for their shared ligands. The anaphylatoxin receptors are expressed in a variety of cells and tissues, e.g. human granulocytes, monocytes, and mast cells. They also seem to be expressed on activated subpopulations of lymphocytes and some other, non-myeloid cells (e.g. of the central nervous system). Anaphylatoxins and their receptors participate in numerous diseases such as adult respiratory distress syndrome, SLE, rheumatoid arthritis, psoriasis, sepsis/SIRS, polytrauma, Arthus reaction, and defense against bacterial infections of the lung, asthma, and colitis.
Our group is focusing on various aspects of anaphylatoxin receptor expression, regulation, signalling, function, and cross-talk between these receptors. We want to gain a detailed understanding of the role of these complement receptors in inflammatory disorders and help to develop inhibitors and modulators within the complement cascade.
Moreover, we are also interested in the involvement of the complement system in the infection with intracellular bacteria such as chlamydia (see above).
METHODS USED IN RESEARCH:
Our work is based on analysis of purified primary cells, generation and characterization of stably and transiently expressing cell lines (HeLa, HEK293, RBL-2H3), and mouse models (colitis, pneumonia) using several mouse strains with gene knock-outs of complement components. We employ a broad range of molecular and cell biological methods including generation and expression of recombinant receptors and their mutants by a retroviral gene transfer and expression system, overexpression of chlamydial effector proteins, overexpression of dominant negative mutants of signalling components, reporter gene assays, competitive binding studies, flow cytometry, trancriptomics, real-time RT-PCR, proteomics, and functional assays addressing cell signalling.
1. Dahlke K, Wrann CD, Sommerfeld O, Sossdorf M, Recknagel P, Sachse S, Winter SW, Klos A, Stahl GL, Ma YX, Claus RA, Reinhart K, Bauer M, Riedemann NC. Distinct different contributions of the alternative and classical complement activation pathway for the innate host response during sepsis. J Immunol. 186: 3066-3075; 2011
2. Amara U, Flierl MA, Rittirsch D, Klos A, Chen H, Acker B, et al. Molecular intercommunication between the complement and coagulation systems. J Immunol. 185(9): 5628-5636; 2010
3. Thalman, J, JaniK K, May M, Sommer K, Ebeling J, Hofmann F, Genth H, Klos A. Actin re-organization induced by Chlamydia trachomatis Serovar D - Evidence for a critical role of the effector protein CT166 Targeting Rac. PLoS ONE. 5(3):e9887; 2010
4. Bleich EM, Martin M, Bleich A, Klos A. The Mongolian gerbil as a model for inflammatory bowel disease. Int J Exp Pathol. 91(3): 281-287; 2010
5. Johswich K, Martin M, Bleich A, Kracht M, Dittrich-Breiholz O, Gessner JE, Suerbaum S, Wende E. Rheinheimer C, Klos A. Role of the C5a receptor (C5aR) in acute and chronic dextran sulfate-induced models of inflammatory bowel disease. Inflamm Bowel Dis. 15(12):1812-1823; 2009
6. Mosa A, Trumstedt C, Eriksson E, Soehnlein O, Heuts F, Janik K, Klos A, Dittrich-Breiholz O, Kracht M, Hidmark Å, Wigzell H, Rottenberg M E. Non-hematopoietic cells control the outcome of infection with Listeria monocytogenes in a NOD1-dependent manner. Infect Immun. 77(7):2908-18; 2009
7. Klos A, Thalmann J, Peters J, Gérard H C, Hudson A P. The transcript profile of persistent Chlamydophila (Chlamydia) pneumoniae in vitro depends on the means by which persistence is induced. FEMS Microbiol Lett. 291:120-126; 2009
8. Sommer K, Njau F, Wittkop U, Thalmann J, Bartling G, Wagner A, Klos A. Identification of high- and low-virulent strains of Chlamydia pneumoniae by their characterization in a mouse Pneumonia Model. FEMS Immunol & Med. Microbiol. 55(2):206-14; 2009
9. Scola A, Johswich K, Morgan B P, Klos A, Monk P N. The human complement fragment receptor, C5L2, is a decoy receptor. Mol Immunol. 46(6):1149-62; 2009
10. Wrann C D, Tabriz N A, Barkhausen T, Klos A, van Griensven M, Pape H C, Kendoff D O, Guo R, Ward P, Krettek C, Riedemann N. The PI3K signaling pathway exerts protective effects during sepsis by controlling C5a-mediated activation of innate immune functions. J Immunol. 178: 5940-5948; 2007
11. Eickhoff M, Thalmann J, Hess S, Martin M, Laue T, Kruppa J, Brandes G, Klos A. Host cell responses to Chlamydia pneumoniae in IFN-γ-induced persistence overlap those of productive infection and are linked to genes involved in apoptosis, cell cycle, and metabolism. Infect Immunity. 75:2853-2863; 2007
12. Johswich K, Martin M, Thalmann J, Rheinheimer C, Monk PN, Klos A. Ligand specificity of the anaphylatoxin C5L2 receptor and its regulation on myeloid and epithelial cell-lines. J Biol Chem. 281:39088-39095; 2006
13. Schaefer M, Konrad S, Thalmann J, Rheinheimer C, Johswich K, Sohns B, Klos A. The transcription factors AP-1 and Ets are regulators of C3a receptor expression. J Biol Chem. 280(51): 42113-42123; 2005
14. Peters J, Hess S, Endlich K, Thalmann J, Holzberg D, Kracht M, Schaefer M, Bartling G, Klos A. Silencing and permanent activation: Host-cell responses in models of persistent Chlamydia pneumoniae infection. Cell Microbiol. 7:1099-1108; 2005
15. Fischer S F, Vier J J, Kirschnek S, Klos A, Hess S, Häcker G. Chlamydia inhibit host cell-apoptosis by specific degradation of the pro-apoptotic BH3-only protein Bim. J Exp Med. 200:905-916; 2004
16. Godau J, Heller T, Hawlisch H, Trappe M, Howells E, Best J, Zwirner J, Verbeek J S, Hogarth P M, Gerard C, van Rooijen N, Klos A, Gessner J E, Köhl J. C5a initiates the inflammatory cascade in immune complex peritonitis. J Immunol. 173:3437-3445; 2004
17. Otto M, Hawlisch H, Monk P N, Mueller M, Klos A, Karp C L, Köhl J. C5a mutants are potent antagonists of the C5a receptor (CD88) and of C5L2: Position 69 is the locus that determines agonism or antagonism. J Biol Chem. 279:142-151; 2004
18. Hess S, Peters J, Bartling G, Rheinheimer C, Magid-Slav M, Tal-Singer R, Klos A. More than just innate immunity: Comparative analysis of C. pneumoniae and C. trachomatis effects on host-cell gene-regulation. Cell Microbiol. 5: 785-795; 2003
19. Settmacher B, Rheinheimer C, Hamacher H, Ames R S, Wise A, Jenkinson L, Bock D, Schaefer M, Köhl J, Klos A. Structure-function studies of the C3a-receptor: C-terminal serine and threonine residues which influence receptor internalization and signaling. Eur J Immunol. 33: 920-927; 2003
20. Hess S, Rheinheimer C, Tidow F, Bartling G, Kaps C, Lauber J, Buer J, Klos A. The reprogrammed host: Chlamydia trachomatis-induced up-regulation of glycoprotein 130 cytokines, transcription factors, and antiapoptotic genes. Arthritis Rheum. 44:2392-2401; 2001
21. Ames R S, Lee D, Foley J J, Jurewicz A J, Tornetta M A, Bautsch W, Settmacher B, Klos A, Erhard K F, Cousins R D, Sulpizio A C, Hieble J P, McCafferty G, Ward K W, Adams J L, Bondinell W E, Underwood D C, Osborn R R, Badger A M, Sarau H M. Identification of a selective nonpeptide antagonist of the anaphylatoxin C3a receptor that demonstrates anti¬inflammatory activity in animal models. J Immunol. 166:6341-6348; 2001
22. Hawlisch H, Muller M, Frank R, Bautsch W, Klos A, Köhl J. Site-specific anti-C3a receptor single-chain antibodies selected by differential panning on cellulose sheets. Anal Biochem. 293:142-145; 2001