R B Currier1; S Alsford1;
1 London School of Hygiene and Tropical Medicine, UK
DiscussionIn contrast to Trypanosoma
brucei gambiense and T. b.
rhodesiense, T. b. brucei is
lysed by apolipoprotein-L1 (apoL1)-containing human serum trypanolytic factors
(TLF), rendering it non-infectious to humans. While the mechanisms of TLF1
uptake, apoL1 membrane integration, and T.
b. gambiense and T. b. rhodesiense apoL1-resistance have been extensively characterised,
our understanding of the range of factors that drive apoL1 action in T. b. brucei is limited. Selecting our
bloodstream-form T. b. brucei RNAi
library with recombinant apoL1 identified an array of factors that supports the
trypanocidal action of apoL1, including six ubiquitin modifiers and
several proteins putatively involved in membrane trafficking. Most
prominent amongst these novel apoL1 sensitivity determinants was a putative ubiquitin
ligase. Intriguingly, while loss of this ubiquitin ligase reduced parasite
sensitivity to apoL1, its loss enhanced parasite sensitivity to TLF1-dominated
normal human serum, indicating that free and TLF1-bound apoL1 have contrasting
modes-of-action. Indeed, loss of the known human serum sensitivity
determinants, p67 (lysosomal associated membrane protein) and the cathepsin-L
regulator, ‘inhibitor of cysteine peptidase’, had no effect on sensitivity to
free apoL1. Our findings highlight a complex network of proteins that
influences apoL1 action, with implications for our understanding of the anti-trypanosomal
action of human serum.