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Abstract
Complement factor D (FD) is a serine protease that plays an essential role in the activation of the alternative pathway (AP) by cleaving complement factor B (FB) and generating the C3 convertases C3(H2 O)Bb and C3bBb. FD is produced mainly from adipose tissue and circulates in an activated form. On the contrary, the other serine proteases of the complement system are mainly synthesized in the liver. The activation mechanism of FD has long been unknown. Recently, a serendipitous discovery in the mechanism of FD activation has been provided by a generation of Masp1 gene knockout mice lacking both the serine protease MASP-1 and its alternative splicing variant MASP-3, designated MASP-1/3-deficient mice. Sera from the MASP-1/3-deficient mice had little-to-no lectin pathway (LP) and AP activity with circulating zymogen or proenzyme FD (pro-FD). Sera from patients with 3MC syndrome carrying mutations in the MASP1 gene also had circulating pro-FD, suggesting that MASP-1 and/or MASP-3 are involved in activation of FD. Here, we summarize the current knowledge of the mechanism of FD activation that was finally elucidated using the sera of mice monospecifically deficient for MASP-1 or MASP-3. Sera of the MASP-1-deficient mice lacked LP activity, but those of the MASP-3-deficient mice lacked AP activity with pro-FD. This review illustrates the pivotal role of MASP-3 in the physiological activation of the AP via activation of FD.
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Affiliation(s)
- Hideharu Sekine
- Department of Immunology, Fukushima Medical University School of Medicine, Fukushima, Japan
| | - Takeshi Machida
- Department of Immunology, Fukushima Medical University School of Medicine, Fukushima, Japan
| | - Teizo Fujita
- Fukushima Prefectural General Hygiene Institute, Fukushima, Japan
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2
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Schubart A, Flohr S, Junt T, Eder J. Low-molecular weight inhibitors of the alternative complement pathway. Immunol Rev 2023; 313:339-357. [PMID: 36217774 PMCID: PMC10092480 DOI: 10.1111/imr.13143] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Dysregulation of the alternative complement pathway predisposes individuals to a number of diseases. It can either be evoked by genetic alterations in or by stabilizing antibodies to important pathway components and typically leads to severe diseases such as paroxysmal nocturnal hemoglobinuria, atypical hemolytic uremic syndrome, C3 glomerulopathy, and age-related macular degeneration. In addition, the alternative pathway may also be involved in many other diseases where its amplifying function for all complement pathways might play a role. To identify specific alternative pathway inhibitors that qualify as therapeutics for these diseases, drug discovery efforts have focused on the two central proteases of the pathway, factor B and factor D. Although drug discovery has been challenging for a number of reasons, potent and selective low-molecular weight (LMW) oral inhibitors have now been discovered for both proteases and several molecules are in clinical development for multiple complement-mediated diseases. While the clinical development of these inhibitors initially focuses on diseases with systemic and/or peripheral tissue complement activation, the availability of LMW inhibitors may also open up the prospect of inhibiting complement in the central nervous system where its activation may also play an important role in several neurodegenerative diseases.
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Affiliation(s)
- Anna Schubart
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Stefanie Flohr
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Tobias Junt
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Jörg Eder
- Novartis Institutes for BioMedical Research, Basel, Switzerland
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3
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Shaughnessy J, Chabeda A, Lewis LA, Ram S. Alternative pathway amplification and infections. Immunol Rev 2023; 313:162-180. [PMID: 36336911 DOI: 10.1111/imr.13160] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The alternative pathway (AP) is the phylogenetically oldest arm of the complement system and may have evolved to mark pathogens for elimination by phagocytes. Studies using purified AP proteins or AP-specific serum showed that C3b amplification on bacteria commenced following a lag phase of about 5 min and was highly dependent on the concentration of complement. Most pathogens have evolved several elegant mechanisms to evade complement, including expressing proteases that degrade AP proteins and secreting proteins that block function of C3 convertases. In an example of convergent evolution, many microbes recruit the AP inhibitor factor H (FH) using molecular mechanisms that mimic FH interactions with host cells. In most instances, the AP serves to amplify C3b deposited on microbes by the classical pathway (CP). The role of properdin on microbes appears to be restricted to stabilization of C3 convertases; scant evidence exists for its role as an initiator of the AP on pathogens in the context of serum. Therapeutic complement inhibition carries with it an increased risk of infection. Antibody (Ab)-dependent AP activation may be critical for complement activation by vaccine-elicited Ab when the CP is blocked, and its molecular mechanism is discussed.
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Affiliation(s)
- Jutamas Shaughnessy
- Division of Infectious Diseases and Immunology, University of Massachusetts Chan Medical School, Worcester, Massachusetts, USA
| | - Aleyo Chabeda
- Division of Infectious Diseases and Immunology, University of Massachusetts Chan Medical School, Worcester, Massachusetts, USA
| | - Lisa A Lewis
- Division of Infectious Diseases and Immunology, University of Massachusetts Chan Medical School, Worcester, Massachusetts, USA
| | - Sanjay Ram
- Division of Infectious Diseases and Immunology, University of Massachusetts Chan Medical School, Worcester, Massachusetts, USA
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4
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Gil E, Noursadeghi M, Brown JS. Streptococcus pneumoniae interactions with the complement system. Front Cell Infect Microbiol 2022; 12:929483. [PMID: 35967850 PMCID: PMC9366601 DOI: 10.3389/fcimb.2022.929483] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Accepted: 07/08/2022] [Indexed: 11/21/2022] Open
Abstract
Host innate and adaptive immunity to infection with Streptococcus pneumoniae is critically dependent on the complement system, demonstrated by the high incidence of invasive S. pneumoniae infection in people with inherited deficiency of complement components. The complement system is activated by S. pneumoniae through multiple mechanisms. The classical complement pathway is activated by recognition of S. pneumoniae by C-reactive protein, serum amyloid P, C1q, SIGN-R1, or natural or acquired antibody. Some S. pneumoniae strains are also recognised by ficolins to activate the mannose binding lectin (MBL) activation pathway. Complement activation is then amplified by the alternative complement pathway, which can also be activated by S. pneumoniae directly. Complement activation results in covalent linkage of the opsonic complement factors C3b and iC3b to the S. pneumoniae surface which promote phagocytic clearance, along with complement-mediated immune adherence to erythrocytes, thereby protecting against septicaemia. The role of complement for mucosal immunity to S. pneumoniae is less clear. Given the major role of complement in controlling infection with S. pneumoniae, it is perhaps unsurprising that S. pneumoniae has evolved multiple mechanisms of complement evasion, including the capsule, multiple surface proteins, and the toxin pneumolysin. There is considerable variation between S. pneumoniae capsular serotypes and genotypes with regards to sensitivity to complement which correlates with ability to cause invasive infections. However, at present we only have a limited understanding of the main mechanisms causing variations in complement sensitivity between S. pneumoniae strains and to non-pathogenic streptococci.
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Affiliation(s)
- Eliza Gil
- Division of Infection and Immunity, University College London, London, United Kingdom
- *Correspondence: Eliza Gil,
| | - Mahdad Noursadeghi
- Division of Infection and Immunity, University College London, London, United Kingdom
| | - Jeremy S. Brown
- Division of Medicine, University College London, London, United Kingdom
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5
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Henriksen ML, Nielsen C, Pedersen D, Andersen GR, Thiel S, Palarasah Y, Hansen SWK. Quantification of the pro-form of human complement component factor D (adipsin). J Immunol Methods 2022; 507:113295. [DOI: 10.1016/j.jim.2022.113295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2022] [Revised: 05/31/2022] [Accepted: 06/01/2022] [Indexed: 11/30/2022]
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Langereis JD, van der Molen RG, de Kat Angelino C, Henriet SS, de Jonge MI, Joosten I, Simons A, Schuurs-Hoeijmakers JH, van Deuren M, van Aerde K, van der Flier M. Complement factor D haplodeficiency is associated with a reduced complement activation speed and diminished bacterial killing. Clin Transl Immunology 2021; 10:e1256. [PMID: 33841879 PMCID: PMC8019133 DOI: 10.1002/cti2.1256] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2020] [Revised: 01/29/2021] [Accepted: 01/29/2021] [Indexed: 01/16/2023] Open
Abstract
Objectives Complete deficiency of alternative pathway (AP) complement factors, explained by homozygous mutations, is a well‐known risk factor for invasive bacterial infections; however, this is less obvious for heterozygous mutations. We describe two siblings with a heterozygous NM_001928.3(CFD):c.125C>A p.(Ser42*) mutation in the complement factor D (fD) gene having a history of recurrent bacterial infections. We determined the effect of heterozygous fD deficiency on AP complement activity. Methods We determined the effect of fD levels on complement activation as measured by AP activity, complement C3 binding to the bacterial surface of Neisseria meningitidis (Nm), Streptococcus pneumoniae (Sp) and non‐typeable Haemophilus influenzae (NTHi), and complement‐mediated killing of Nm and NTHi. In addition, we measured the effect of vaccination of complement C3 binding to the bacterial surface and killing of Nm. Results Reconstitution of fD‐deficient serum with fD increased AP activity in a dose‐ and time‐dependent way. Reconstitution of patient serum with fD to normal levels increased complement C3 binding to Sp, Nm and NTHi, as well as complement‐mediated killing of Nm and NTHi. Vaccination increased complement C3 binding and resulted in complete killing of Nm without fD reconstitution. Conclusion We conclude that low fD serum levels (< 0.5 μg mL−1) lead to a reduced speed of complement activation, which results in diminished bacterial killing, consistent with recurrent bacterial infections observed in our index patients. Specific antibodies induced by vaccination are able to overcome the diminished bacterial killing capacity in patients with low fD levels.
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Affiliation(s)
- Jeroen D Langereis
- Department of Laboratory Medicine Laboratory of Medical Immunology Radboud Institute for Molecular Life Sciences Radboudumc Nijmegen The Netherlands.,Radboud Center for Infectious Diseases Radboudumc Nijmegen The Netherlands
| | - Renate G van der Molen
- Department of Laboratory Medicine Laboratory of Medical Immunology Radboud Institute for Molecular Life Sciences Radboudumc Nijmegen The Netherlands
| | - Corrie de Kat Angelino
- Department of Laboratory Medicine Laboratory of Medical Immunology Radboud Institute for Molecular Life Sciences Radboudumc Nijmegen The Netherlands
| | - Stefanie S Henriet
- Pediatric Infectious Diseases and Immunology Amalia Children's Hospital Nijmegen The Netherlands.,Expertise Center for Immunodeficiency and Autoinflammation (REIA) Radboudumc Nijmegen The Netherlands
| | - Marien I de Jonge
- Department of Laboratory Medicine Laboratory of Medical Immunology Radboud Institute for Molecular Life Sciences Radboudumc Nijmegen The Netherlands.,Radboud Center for Infectious Diseases Radboudumc Nijmegen The Netherlands
| | - Irma Joosten
- Department of Laboratory Medicine Laboratory of Medical Immunology Radboud Institute for Molecular Life Sciences Radboudumc Nijmegen The Netherlands
| | - Annet Simons
- Department of Human Genetics Radboudumc Nijmegen The Netherlands
| | | | - Marcel van Deuren
- Expertise Center for Immunodeficiency and Autoinflammation (REIA) Radboudumc Nijmegen The Netherlands.,Department of Internal Medicine Division of Infectious Diseases Radboudumc Nijmegen The Netherlands
| | - Koen van Aerde
- Pediatric Infectious Diseases and Immunology Amalia Children's Hospital Nijmegen The Netherlands.,Expertise Center for Immunodeficiency and Autoinflammation (REIA) Radboudumc Nijmegen The Netherlands
| | - Michiel van der Flier
- Pediatric Infectious Diseases and Immunology Amalia Children's Hospital Nijmegen The Netherlands.,Expertise Center for Immunodeficiency and Autoinflammation (REIA) Radboudumc Nijmegen The Netherlands.,Present address: Pediatric Infectious Diseases and Immunology Wilhelmina Children's Hospital UMC Utrecht Utrecht The Netherlands
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7
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Wiles JA, Galvan MD, Podos SD, Geffner M, Huang M. Discovery and Development of the Oral Complement Factor D Inhibitor Danicopan (ACH-4471). Curr Med Chem 2020; 27:4165-4180. [PMID: 31573880 DOI: 10.2174/0929867326666191001130342] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2018] [Revised: 03/28/2019] [Accepted: 04/04/2019] [Indexed: 12/29/2022]
Abstract
Complement plays a vital role in our innate immune defense against invasive microorganisms. Excessive complement activation or insufficient control of activation on host cells, however, is associated with several chronic disorders. Essential to the activation and amplification of the Alternative Pathway (AP) of complement, Complement Factor D (CFD) is a specific serine protease that cleaves its unique substrate, Complement Factor B (CFB) in complex with an activated form of complement component 3 (C3), to generate the AP C3 convertases C3(H2O)Bb and C3bBb. These convertases comprise a central component in eliciting effector responses following AP activation, and they also enable a powerful amplification loop for both the Classical Pathway (CP) and Lectin Pathway (LP) of complement. Because CFD is not required for the activation of either the CP or LP, selective CFD inhibition presents a favorable therapeutic approach to modulating complement activity that leaves intact the effector functions following CP and LP activation and thus poses a lower risk of bacterial infection than other complement-directed approaches. This review provides an update on inhibitors of CFD, which have evolved from irreversible small molecules that demonstrate poor selectivity to reversible small molecules and monoclonal antibodies that demonstrate exceptional selectivity and potency. The reversible small-molecule inhibitor danicopan.
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Affiliation(s)
- Jason A Wiles
- Drug Discovery, Achillion Pharmaceuticals, New Haven, CT 06511, United States
| | - Manuel D Galvan
- Drug Discovery, Achillion Pharmaceuticals, New Haven, CT 06511, United States
| | - Steven D Podos
- Drug Discovery, Achillion Pharmaceuticals, New Haven, CT 06511, United States
| | - Michael Geffner
- Drug Development, Achillion Pharmaceuticals, New Haven, CT 06511, United States
| | - Mingjun Huang
- Drug Discovery, Achillion Pharmaceuticals, New Haven, CT 06511, United States
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8
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van den Broek B, van der Flier M, de Groot R, de Jonge MI, Langereis JD. Common Genetic Variants in the Complement System and their Potential Link with Disease Susceptibility and Outcome of Invasive Bacterial Infection. J Innate Immun 2019; 12:131-141. [PMID: 31269507 DOI: 10.1159/000500545] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Accepted: 04/19/2019] [Indexed: 01/01/2023] Open
Abstract
Streptococcus pneumoniae and Neisseria meningitidis are pathogens that frequently colonize the nasopharynx in an asymptomatic manner but are also a cause of invasive bacterial infections mainly in young children. The complement system plays a crucial role in humoral immunity, complementing the ability of antibodies to clear microbes, thereby protecting the host against bacterial infections, including S. pneumoniae and N. meningitidis. While it is widely accepted that complement deficiencies due to rare genetic variants increase the risk for invasive bacterial infection, not much is known about the common genetic variants in the complement system in relation to disease susceptibility. In this review, we provide an overview of the effects of common genetic variants on complement activation and on complement-mediated inflammation.
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Affiliation(s)
- Bryan van den Broek
- Paediatric Infectious Diseases and Immunology, Amalia Children's Hospital, Nijmegen, The Netherlands.,Section Paediatric Infectious Diseases, Laboratory of Medical Immunology, Radboud Institute for Molecular Life Sciences, Radboudumc, Nijmegen, The Netherlands.,Radboud Center for Infectious Diseases, Radboudumc, Nijmegen, The Netherlands
| | - Michiel van der Flier
- Paediatric Infectious Diseases and Immunology, Amalia Children's Hospital, Nijmegen, The Netherlands.,Expertise Center for Immunodeficiency and Auto inflammation (REIA), Radboudumc, Nijmegen, The Netherlands.,Section Paediatric Infectious Diseases, Laboratory of Medical Immunology, Radboud Institute for Molecular Life Sciences, Radboudumc, Nijmegen, The Netherlands.,Radboud Center for Infectious Diseases, Radboudumc, Nijmegen, The Netherlands
| | - Ronald de Groot
- Section Paediatric Infectious Diseases, Laboratory of Medical Immunology, Radboud Institute for Molecular Life Sciences, Radboudumc, Nijmegen, The Netherlands.,Radboud Center for Infectious Diseases, Radboudumc, Nijmegen, The Netherlands
| | - Marien I de Jonge
- Section Paediatric Infectious Diseases, Laboratory of Medical Immunology, Radboud Institute for Molecular Life Sciences, Radboudumc, Nijmegen, The Netherlands.,Radboud Center for Infectious Diseases, Radboudumc, Nijmegen, The Netherlands
| | - Jeroen D Langereis
- Section Paediatric Infectious Diseases, Laboratory of Medical Immunology, Radboud Institute for Molecular Life Sciences, Radboudumc, Nijmegen, The Netherlands, .,Radboud Center for Infectious Diseases, Radboudumc, Nijmegen, The Netherlands,
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Yuan X, Gavriilaki E, Thanassi JA, Yang G, Baines AC, Podos SD, Huang Y, Huang M, Brodsky RA. Small-molecule factor D inhibitors selectively block the alternative pathway of complement in paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome. Haematologica 2016; 102:466-475. [PMID: 27810992 PMCID: PMC5394948 DOI: 10.3324/haematol.2016.153312] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Accepted: 10/24/2016] [Indexed: 12/13/2022] Open
Abstract
Paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome are diseases of excess activation of the alternative pathway of complement that are treated with eculizumab, a humanized monoclonal antibody against the terminal complement component C5. Eculizumab must be administered intravenously, and moreover some patients with paroxysmal nocturnal hemoglobinuria on eculizumab have symptomatic extravascular hemolysis, indicating an unmet need for additional therapeutic approaches. We report the activity of two novel small-molecule inhibitors of the alternative pathway component Factor D using in vitro correlates of both paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome. Both compounds bind human Factor D with high affinity and effectively inhibit its proteolytic activity against purified Factor B in complex with C3b. When tested using the traditional Ham test with cells from paroxysmal nocturnal hemoglobinuria patients, the Factor D inhibitors significantly reduced complement-mediated hemolysis at concentrations as low as 0.01 μM. Additionally the compound ACH-4471 significantly decreased C3 fragment deposition on paroxysmal nocturnal hemoglobinuria erythrocytes, indicating a reduced potential relative to eculizumab for extravascular hemolysis. Using the recently described modified Ham test with serum from patients with atypical hemolytic uremic syndrome, the compounds reduced the alternative pathway-mediated killing of PIGA-null reagent cells, thus establishing their potential utility for this disease of alternative pathway of complement dysregulation and validating the modified Ham test as a system for pre-clinical drug development for atypical hemolytic uremic syndrome. Finally, ACH-4471 blocked alternative pathway activity when administered orally to cynomolgus monkeys. In conclusion, the small-molecule Factor D inhibitors show potential as oral therapeutics for human diseases driven by the alternative pathway of complement, including paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome.
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Affiliation(s)
- Xuan Yuan
- Division of Hematology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Eleni Gavriilaki
- Division of Hematology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | | | | | - Andrea C Baines
- Division of Hematology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | | | | | | | - Robert A Brodsky
- Division of Hematology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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10
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Infections of people with complement deficiencies and patients who have undergone splenectomy. Clin Microbiol Rev 2010; 23:740-80. [PMID: 20930072 DOI: 10.1128/cmr.00048-09] [Citation(s) in RCA: 252] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The complement system comprises several fluid-phase and membrane-associated proteins. Under physiological conditions, activation of the fluid-phase components of complement is maintained under tight control and complement activation occurs primarily on surfaces recognized as "nonself" in an attempt to minimize damage to bystander host cells. Membrane complement components act to limit complement activation on host cells or to facilitate uptake of antigens or microbes "tagged" with complement fragments. While this review focuses on the role of complement in infectious diseases, work over the past couple of decades has defined several important functions of complement distinct from that of combating infections. Activation of complement in the fluid phase can occur through the classical, lectin, or alternative pathway. Deficiencies of components of the classical pathway lead to the development of autoimmune disorders and predispose individuals to recurrent respiratory infections and infections caused by encapsulated organisms, including Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae. While no individual with complete mannan-binding lectin (MBL) deficiency has been identified, low MBL levels have been linked to predisposition to, or severity of, several diseases. It appears that MBL may play an important role in children, who have a relatively immature adaptive immune response. C3 is the point at which all complement pathways converge, and complete deficiency of C3 invariably leads to severe infections, including those caused by meningococci and pneumococci. Deficiencies of the alternative and terminal complement pathways result in an almost exclusive predisposition to invasive meningococcal disease. The spleen plays an important role in antigen processing and the production of antibodies. Splenic macrophages are critical in clearing opsonized encapsulated bacteria (such as pneumococci, meningococci, and Escherichia coli) and intraerythrocytic parasites such as those causing malaria and babesiosis, which explains the fulminant nature of these infections in persons with anatomic or functional asplenia. Paramount to the management of patients with complement deficiencies and asplenia is educating patients about their predisposition to infection and the importance of preventive immunizations and seeking prompt medical attention.
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Xu Y, Ma M, Ippolito GC, Schroeder HW, Carroll MC, Volanakis JE. Complement activation in factor D-deficient mice. Proc Natl Acad Sci U S A 2001; 98:14577-82. [PMID: 11724962 PMCID: PMC64724 DOI: 10.1073/pnas.261428398] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2001] [Indexed: 01/12/2023] Open
Abstract
To assess the contribution of the alternative pathway in complement activation and host defense and its possible role in the regulation of systemic energy balance in vivo, factor D-deficient mice were generated by gene targeting. The mutant mice have no apparent abnormality in development and their body weights are similar to those of factor D-sufficient littermates. Complement activation could not be initiated in the serum of deficient mice by the alternative pathway activators rabbit erythrocytes and zymosan. Surprisingly, injection of cobra venom factor (CVF) caused a profound and reproducible reduction in serum C3 levels, whereas, as expected, there was no C3 reduction in factor B-deficient mice treated similarly. Studies of C3 and factor B activation in vitro by CVF demonstrated that in factor D-deficient serum the alpha chain of C3 was cleaved gradually over a period of 60 min without detectable cleavage of factor B. CVF-dependent C3 cleavage in the deficient serum required the presence of Mg(2+), whereas in normal mouse serum the presence of divalent cations was not required. These results suggest that in mouse proteolytic cleavage of factor B by factor D is not an absolute requirement for the zymogen to active enzyme conformational transition of CVF-bound factor B. Kinetics of opsonization of Streptococcus pneumoniae by C3 fragments was much slower in factor D-deficient serum, suggesting a significant contribution of the alternative pathway to antibacterial host defense early after infection.
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Affiliation(s)
- Y Xu
- Department of Medicine, University of Alabama, Birmingham, AL 35294, USA.
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12
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Biesma DH, Hannema AJ, van Velzen-Blad H, Mulder L, van Zwieten R, Kluijt I, Roos D. A family with complement factor D deficiency. J Clin Invest 2001. [DOI: 10.1172/jci200112023] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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13
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Biesma DH, Hannema AJ, van Velzen-Blad H, Mulder L, van Zwieten R, Kluijt I, Roos D. A family with complement factor D deficiency. J Clin Invest 2001; 108:233-40. [PMID: 11457876 PMCID: PMC203023 DOI: 10.1172/jci12023] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
A complement factor D deficiency was found in a young woman who had experienced a serious Neisseria meningitidis infection, in a deceased family member with a history of meningitis, and in three relatives without a history of serious infections. The patient and these three relatives showed a normal activity of the classical complement pathway, but a very low activity of the alternative complement pathway and a very low capacity to opsonize Escherichia coli and N. meningitidis (isolated from the patient) for phagocytosis by normal human neutrophils. The alternative pathway-dependent hemolytic activity and the opsonizing capacity of these sera were restored by addition of purified factor D. The family had a high degree of consanguinity, and several other family members exhibited decreased levels of factor D. The gene encoding factor D was found to contain a point mutation that changed the TCG codon for serine 42 into a TAG stop codon. This mutation was found in both alleles of the five completely factor D-deficient family members and in one allele of 21 other members of the same family who had decreased or low-normal factor D levels in their serum. The gene sequence of the signal peptide of human factor D was also identified. Our report is the first, to our knowledge, to document a Factor D gene mutation. The mode of inheritance of factor D deficiency is autosomal recessive, in accordance with the localization of the Factor D gene on chromosome 19. Increased susceptibility for infections in individuals with a partial factor D deficiency is unlikely.
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Affiliation(s)
- D H Biesma
- Department of Internal Medicine, St. Antonius Hospital, Nieuwegein, The Netherlands.
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