Localization of serum resistance-associated protein in Trypanosoma brucei rhodesiense and transgenic Trypanosoma brucei brucei.

African trypanosomes infect a broad range of mammals, but humans and some higher primates are protected by serum trypanosome lytic factors that contain apolipoprotein L1 (ApoL1). In the human-infective subspecies of Trypanosoma brucei, Trypanosoma brucei rhodesiense, a gene product derived from the variant surface glycoprotein gene family member, serum resistance-associated protein (SRA protein), protects against ApoL1-mediated lysis. Protection against trypanosome lytic factor requires the direct interaction between SRA protein and ApoL1 within the endocytic apparatus of the trypanosome, but some uncertainty remains as to the precise mechanism and location of this interaction. In order to provide more insight into the mechanism of SRA-mediated resistance to trypanosome lytic factor, we assessed the localization of SRA in T. b. rhodesiense EATRO3 using a novel monoclonal antibody raised against SRA together with a set of well-characterized endosomal markers. By three-dimensional deconvolved immunofluorescence single-cell analysis, combined with double-labelling immunoelectron microscopy, we found that ≈ 50% of SRA protein localized to the lysosome, with the remaining population being distributed through the endocytic pathway, but apparently absent from the flagellar pocket membrane. These data suggest that the SRA/trypanolytic factor interaction is intracellular, with the concentration within the endosomes potentially crucial for ensuring a high efficiency.MN is funded by grants from the Spanish Ministerio de Ciencia e Innovación, (SAF2012-40029), Junta de Andalucia (CTS-5841) and VI PN de I+D+I 2008–2011, Instituto de Salud Carlos III – Subdirección General de Redes y Centros de Investigación Cooperativa (RICET) RD12/0018/0001 and RD12/0018/0015. J-MB is supported by a Miguel Servet Fellowship (CP09/00300) and funded by ‘Fondo de Investigación Sanitaria’ PI10/01128. JR and MC were funded by a Wellcome Trust Project Grant 093008/Z/10/Z. Work in the Dundee laboratory was funded by the Wellcome Trust (program grant 093008/Z/10/Z) and the Medical Research Council.This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1111/cmi.1245