Apolipoprotein L1 Variant Associated with Increased Susceptibility to Trypanosome Infection

12 Apr 2016
Bart Cuypers, Laurence Lecordier, Conor J. Meehan, Frederik Van den Broeck, Hideo Imamura, Philippe B├╝scher, Jean-Claude Dujardin, Kris Laukens, Achim Schnaufer, Caroline Dewar, Michael Lewis, Oliver Balmer, Thomas Azurago, Sardick Kyei-Faried, Sally-Ann Ohene, Boateng Duah, Prince Homiah, Ebenezer Kofi Mensah, Francis Anleah, Jose Ramon Franco, Etienne Pays, Stijn Deborggraeve

African trypanosomes, except Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense, which cause human African trypanosomiasis, are lysed by the human serum protein apolipoprotein L1 (ApoL1). These two subspecies can resist human ApoL1 because they express the serum resistance proteins T. b. gambiense glycoprotein (TgsGP) and serum resistance-associated protein (SRA), respectively. Whereas in T. b. rhodesiense, SRA is necessary and sufficient to inhibit ApoL1, in T. b. gambiense, TgsGP cannot protect against high ApoL1 uptake, so different additional mechanisms contribute to limit this uptake. Here we report a complex interplay between trypanosomes and an ApoL1 variant, revealing important insights into innate human immunity against these parasites. Using whole-genome sequencing, we characterized an atypical T. b. gambiense infection in a patient in Ghana. We show that the infecting trypanosome has diverged from the classical T. b. gambiense strains and lacks the TgsGP defense mechanism against human serum. By sequencing the ApoL1 gene of the patient and subsequent in vitro mutagenesis experiments, we demonstrate that a homozygous missense substitution (N264K) in the membrane-addressing domain of this ApoL1 variant knocks down the trypanolytic activity, allowing the trypanosome to avoid ApoL1-mediated immunity.