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Immune evasion of pathogenic moulds by acquisition of complement factor H and C4b binding protein
Abstracts / Molecular Immunology 44 (2007) 3909–3994
O39 Hematin promotes complement alternative pathwaymediated deposition of C3 activation fragments on human erythrocytes: Potential implications for the pathogenesis of anemia in malaria Ronald P. Taylor a , Andrew W. Pawluczkowycz a , Margaret A. Lindorfer a , John W. Waitumbi b a
Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, Virginia 22908, USA b Walter Reed Project and Kenya Medical Research Institute, Kisumu, Kenya Childhood malaria caused by Plasmodium falciparum (pf) is often characterized by severe anemia at low parasite burdens; the mechanism(s) responsible for this pathology remain to be defined. We have reported that erythrocyte (E) CR1, the immune adherence receptor specific for C3b, is reduced during anemia in childhood malaria, suggesting a possible role for complement in E destruction. Intravascular lysis of infected E by pf leads to release of E breakdown products hemoglobin and hematin, which have inflammatory properties. Free hematin can bind to E, and we find that in serum and in citrated whole blood, moderate concentrations of hematin activate the alternative pathway of complement and promote deposition of C3 activation and breakdown products on E. The degree of C3 fragment deposition is directly correlated with E CR1 levels, both within a given donor’s E population and when E from different donors are compared. E opsonized with complement in the presence of hematin form rosettes with Raji cells, through interaction with CR2, the C3dg receptor expressed on several types of B cells including splenic marginal zone B cells. Thus, hematin-mediated complement activation and C3 fragment deposition on E may promote accelerated splenic clearance of the youngest E, which have the most CR1, leading to sudden onset of anemia along with reduction of mean CR1 on surviving E. A monoclonal antibody specific for C3b, mAb 3E7, previously demonstrated to inhibit the alternative pathway of complement, completely blocks the C3 fragment deposition reaction. Use of this monoclonal antibody in non-human primate models of malaria may provide insight into mechanisms of erythrocyte destruction and thus aid in the development of targeted therapies based on inhibiting the alternative pathway of complement. doi:10.1016/j.molimm.2007.06.046
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O40 Immune evasion of pathogenic moulds by acquisition of complement factor H and C4b binding protein G. Vogl 1 , I. Lesiak 1 , C. Speth, C. Lass-Fl¨orl, P.E. Zipfel, A.M. Blom, M.P. Dierich, R. W¨urzner Med. Univ. Innsbruck, Univ. Jena, Univ. Lund, Sweden Pathogenic fungi represent a major threat to immunocompromised hosts, leading to severe, and often lethal, systemic opportunistic infections. Factor H (FH), a soluble plasma protein consisting of 20 short consensus repeats (SCRs), is the main fluid phase inhibitor of the alternative pathway of complement. C4b-binding protein (C4bp), having a polymeric structure composed of 6–8 identical ␣-chains and a single -chain, is the main fluid-phase inhibitor of the classical and lectin pathways of complement. Both proteins can be acquired onto the surface of various human pathogens conveying resistance to complement destruction and thus contributing to their pathogenic potential. We have recently shown that Candida albicans evades complement by binding both FH and C4bp. We now show that moulds such as Aspergillus spp. do not only bind the complete form of FH and its splicing product FHL-1 (consisting of FH SCRs 1–7), but also C4bp. Immunofluorescence and flow cytometry studies detail that FH and C4bp binding to Aspergillus spp. appears to be even stronger than to Candida spp. and that different albeit possibly nearby binding moieties are involved. doi:10.1016/j.molimm.2007.06.047 Session 7: Complement structure and function Tuesday 11th September 08.30–10.30 O41 Structural studies of the interaction of SITE 2 of CR1 (CD35) with C3b and C4b Thomas J. Allen a , Richard Hauhart b , Paul Barlow c , John P. Atkinson b a
Division of Pediatric Infectious Diseases, Washington University School of Medicine, St. Louis, MO 63110, USA b Division of Rheumatology, Washington University School of Medicine, St. Louis, MO 63110, USA c School of Biological Sciences, University of Edinburgh, Edinburgh, UK The binding interaction (immune adherence) of CR1 with C3b and C4b plays a fundamental role in innate and adaptive immunity. A molecular model of this interplay may provide insight into a growing list of pathologic processes attributed to mutations and polymorphisms in the regulators of complement activation genes. In this light, we continue to expand upon our previous efforts to elucidate the structural details of interaction of CR1 with its ligands. 1
These authors contributed equally.
O39 Hematin promotes complement alternative pathwaymediated deposition of C3 activation fragments on human erythrocytes: Potential implications for the pathogenesis of anemia in malaria Ronald P. Taylor a , Andrew W. Pawluczkowycz a , Margaret A. Lindorfer a , John W. Waitumbi b a
Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, Virginia 22908, USA b Walter Reed Project and Kenya Medical Research Institute, Kisumu, Kenya Childhood malaria caused by Plasmodium falciparum (pf) is often characterized by severe anemia at low parasite burdens; the mechanism(s) responsible for this pathology remain to be defined. We have reported that erythrocyte (E) CR1, the immune adherence receptor specific for C3b, is reduced during anemia in childhood malaria, suggesting a possible role for complement in E destruction. Intravascular lysis of infected E by pf leads to release of E breakdown products hemoglobin and hematin, which have inflammatory properties. Free hematin can bind to E, and we find that in serum and in citrated whole blood, moderate concentrations of hematin activate the alternative pathway of complement and promote deposition of C3 activation and breakdown products on E. The degree of C3 fragment deposition is directly correlated with E CR1 levels, both within a given donor’s E population and when E from different donors are compared. E opsonized with complement in the presence of hematin form rosettes with Raji cells, through interaction with CR2, the C3dg receptor expressed on several types of B cells including splenic marginal zone B cells. Thus, hematin-mediated complement activation and C3 fragment deposition on E may promote accelerated splenic clearance of the youngest E, which have the most CR1, leading to sudden onset of anemia along with reduction of mean CR1 on surviving E. A monoclonal antibody specific for C3b, mAb 3E7, previously demonstrated to inhibit the alternative pathway of complement, completely blocks the C3 fragment deposition reaction. Use of this monoclonal antibody in non-human primate models of malaria may provide insight into mechanisms of erythrocyte destruction and thus aid in the development of targeted therapies based on inhibiting the alternative pathway of complement. doi:10.1016/j.molimm.2007.06.046
3927
O40 Immune evasion of pathogenic moulds by acquisition of complement factor H and C4b binding protein G. Vogl 1 , I. Lesiak 1 , C. Speth, C. Lass-Fl¨orl, P.E. Zipfel, A.M. Blom, M.P. Dierich, R. W¨urzner Med. Univ. Innsbruck, Univ. Jena, Univ. Lund, Sweden Pathogenic fungi represent a major threat to immunocompromised hosts, leading to severe, and often lethal, systemic opportunistic infections. Factor H (FH), a soluble plasma protein consisting of 20 short consensus repeats (SCRs), is the main fluid phase inhibitor of the alternative pathway of complement. C4b-binding protein (C4bp), having a polymeric structure composed of 6–8 identical ␣-chains and a single -chain, is the main fluid-phase inhibitor of the classical and lectin pathways of complement. Both proteins can be acquired onto the surface of various human pathogens conveying resistance to complement destruction and thus contributing to their pathogenic potential. We have recently shown that Candida albicans evades complement by binding both FH and C4bp. We now show that moulds such as Aspergillus spp. do not only bind the complete form of FH and its splicing product FHL-1 (consisting of FH SCRs 1–7), but also C4bp. Immunofluorescence and flow cytometry studies detail that FH and C4bp binding to Aspergillus spp. appears to be even stronger than to Candida spp. and that different albeit possibly nearby binding moieties are involved. doi:10.1016/j.molimm.2007.06.047 Session 7: Complement structure and function Tuesday 11th September 08.30–10.30 O41 Structural studies of the interaction of SITE 2 of CR1 (CD35) with C3b and C4b Thomas J. Allen a , Richard Hauhart b , Paul Barlow c , John P. Atkinson b a
Division of Pediatric Infectious Diseases, Washington University School of Medicine, St. Louis, MO 63110, USA b Division of Rheumatology, Washington University School of Medicine, St. Louis, MO 63110, USA c School of Biological Sciences, University of Edinburgh, Edinburgh, UK The binding interaction (immune adherence) of CR1 with C3b and C4b plays a fundamental role in innate and adaptive immunity. A molecular model of this interplay may provide insight into a growing list of pathologic processes attributed to mutations and polymorphisms in the regulators of complement activation genes. In this light, we continue to expand upon our previous efforts to elucidate the structural details of interaction of CR1 with its ligands. 1
These authors contributed equally.