Trypanosome Lytic Factor-1 Initiates Oxidation-stimulated Osmotic Lysis of Trypanosoma brucei brucei

J Biol Chem. 2016 Feb 5;291(6):3063-75. doi: 10.1074/jbc.M115.680371. Epub 2015 Dec 8.


Human innate immunity against the veterinary pathogen Trypanosoma brucei brucei is conferred by trypanosome lytic factors (TLFs), against which human-infective T. brucei gambiense and T. brucei rhodesiense have evolved resistance. TLF-1 is a subclass of high density lipoprotein particles defined by two primate-specific apolipoproteins: the ion channel-forming toxin ApoL1 (apolipoprotein L1) and the hemoglobin (Hb) scavenger Hpr (haptoglobin-related protein). The role of oxidative stress in the TLF-1 lytic mechanism has been controversial. Here we show that oxidative processes are involved in TLF-1 killing of T. brucei brucei. The lipophilic antioxidant N,N'-diphenyl-p-phenylenediamine protected TLF-1-treated T. brucei brucei from lysis. Conversely, lysis of TLF-1-treated T. brucei brucei was increased by the addition of peroxides or thiol-conjugating agents. Previously, the Hpr-Hb complex was postulated to be a source of free radicals during TLF-1 lysis. However, we found that the iron-containing heme of the Hpr-Hb complex was not involved in TLF-1 lysis. Furthermore, neither high concentrations of transferrin nor knock-out of cytosolic lipid peroxidases prevented TLF-1 lysis. Instead, purified ApoL1 was sufficient to induce lysis, and ApoL1 lysis was inhibited by the antioxidant DPPD. Swelling of TLF-1-treated T. brucei brucei was reminiscent of swelling under hypotonic stress. Moreover, TLF-1-treated T. brucei brucei became rapidly susceptible to hypotonic lysis. T. brucei brucei cells exposed to peroxides or thiol-binding agents were also sensitized to hypotonic lysis in the absence of TLF-1. We postulate that ApoL1 initiates osmotic stress at the plasma membrane, which sensitizes T. brucei brucei to oxidation-stimulated osmotic lysis.

Keywords: Trypanosoma brucei; cell death; innate immunity; osmotic swelling; oxidative stress; parasite; trypanosome.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apolipoprotein L1
  • Apolipoproteins / metabolism
  • Apolipoproteins / pharmacology
  • Cell Membrane / genetics
  • Cell Membrane / metabolism*
  • Free Radicals / metabolism
  • Gene Knockdown Techniques
  • Humans
  • Lipoproteins, HDL / metabolism
  • Lipoproteins, HDL / pharmacology*
  • Osmotic Pressure / drug effects*
  • Oxidation-Reduction / drug effects
  • Oxidative Stress / drug effects*
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism
  • Trypanosoma brucei brucei / genetics
  • Trypanosoma brucei brucei / metabolism*


  • APOL1 protein, human
  • Apolipoprotein L1
  • Apolipoproteins
  • Free Radicals
  • Lipoproteins, HDL
  • Protozoan Proteins
  • TLF1 protein, human