Review Alternative complement pathway assessment in patients with atypical HUS Lubka T. Roumenina a,b,c, ⁎, Chantal Loirat d , Marie-Agnes Dragon-Durey a,b,c,e , Lise Halbwachs-Mecarelli f,c , Catherine Sautes-Fridman a,b,c , Veronique Fremeaux-Bacchi a,b,c,e, ⁎ a Cordeliers Research Center, INSERM UMRS 872, 75006 Paris, France b Université Pierre et Marie Curie (UPMC-Paris-6), 75006 Paris, France c Université Paris Descartes, 75 006 Paris, France d Service de Néphrologie Pédiatrique, Hôpital Robert-Debré, 75935 Paris cedex 19, France e Assistance Publique-Hopitaux de Paris, Hopital Europeen Georges-Pompidou, Service d'Immunologie Biologique, 75908 Paris Cedex 15, France f INSERM U845, Hôpital Necker, 75743 Paris Cedex 15, France article info abstract Article history: Received 30 June 2010 Received in revised form 31 October 2010 Accepted 30 December 2010 Available online 6 January 2011 The atypical Hemolytic Uremic Syndrome (aHUS) is a rare thrombotic microangiopathy leading to end stage renal disease in approximately 60% of patients. Over the last decade, a clear link has been demonstrated between this disease and defective complement regulation. The hallmark of the aHUS is the association with mutations in complement alternative pathway genes. Endothelial damage is related to complement dysregulation, but the exact mechanism is just starting to be elucidated. Screening for and characterization of mutations in the components of the C3 convertase (C3 and FB) or its regulators (FH, FI, MCP, and Thrombomodulin) or anti-FH antibodies has become an indispensable part of the disease's diagnostic. This review will initially summarize current knowledge on the understanding of complement activation and regulation, followed by a description on the genetic analysis as well as the methods used for complement protein quantification. Another part of this review will focus on the mechanisms of action of aHUS-associated mutations. We will emphasize on when and why some mutations lead to protein deficiency, while others result in — to dysfunctional but normally expressed proteins. Finally, we will discuss how the therapy of aHUS patients can be modified according to the functional consequences of each particular genetic defect. © 2011 Elsevier B.V. All rights reserved. Keywords: Atypical Hemolytic Uremic Syndrome Complement Complement blockers Factor H C3 convertase Defective complement regulators Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.1. Molecular mechanisms of the alternative complement pathway activation and regulation . . . . . . . . . . . . . . . . 9 1.2. Complement and atypical Hemolytic Uremic Syndrome (aHUS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.3. Recommendation for complement assessment in patients with aHUS . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.4. Alternative pathway mutations analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.4.1. The amount of the protein matters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.4.2. Deep look into the genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.4.3. Predicting the functional consequences of found mutations . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.4.4. The tools of the trade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 1.4.5. From mutations analysis to the mechanism of the alternative pathway C3 convertase dysregulation in aHUS . . 22 Journal of Immunological Methods 365 (2011) 8–26 ⁎ Corresponding authors. Fremeaux-Bacchi is to be contacted at Service d'Immunologie Biologique, Hôpital Européen Georges Pompidou, 20-40 rue Leblanc, 75908 Paris cedex 15, France. Tel.: +33 1 56 09 39 41; fax: +33 1 56 09 20 80. Roumenina, Cordeliers Research Center, INSERM UMRS 872, Team 13; 15 rue de l'Ecole de Medecine, entrance E, fl. 3; 75006 Paris, France. Tel.: +33 1 44 27 90 96; fax: +33 1 40 51 04 20. E-mail addresses: lubka.roumenina@crc.jussieu.fr (L.T. Roumenina), veronique.fremeaux-bacchi@egp.aphp.fr (V. Fremeaux-Bacchi). 0022-1759/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jim.2010.12.020 Contents lists available at ScienceDirect Journal of Immunological Methods journal homepage: www.elsevier.com/locate/jim