Structures of C1-IgG1 provide insights into how danger pattern recognition activates complement. - Ugurlar D; Howes SC; de Kreuk BJ; Koning RI; de Jong RN; Beurskens FJ; Schuurman J; Koster AJ; Sharp TH; Parren PWHI; Gros P (Science (New York, N.Y.), 2018)