APOL1 expression is induced by Trypanosoma brucei gambiense infection but is not associated with differential susceptibility to sleeping sickness.

Most African trypanosome species are sensitive to trypanolytic factors (TLFs) present in human serum. Trypanosome lysis was demonstrated to be associated with apolipoprotein L-I (APOL1). Trypanosoma brucei (T. b.) gambiense and Trypanosoma brucei rhodesiense, the two human infective trypanosome species, have both developed distinct resistance mechanisms to APOL1 mediated lysis. Whereas T. b. rhodesiense resistance is linked with the expression of the serum resistance associated (SRA) protein that interacts with APOL1 inside the parasite lysosome, inhibiting its lytic action; T. b. gambiense resistance is rather controlled by a reduced expression of the parasite HpHb receptor, limiting APOL1 absorption by trypanosomes. Based on this last observation we hypothesised that variation in the host APOL1 environment could significantly alter T. b. gambiense growth and thus resistance/susceptibility to sleeping sickness. To test this hypothesis, we have measured blood APOL1 relative expression in HAT patients, uninfected endemic controls and serologically positive subjects (SERO TL(+)) that are suspected to control infection to parasitological levels that are undetectable by the available test used in the field. All RNA samples were obtained from medical surveys led in the HAT mangrove foci of Coastal Guinea. Results indicate that APOL1 expression is a complex trait dependant on a variety of factors that need to be taken into account in the analysis. Nevertheless, multivariate analysis showed that APOL1 expression levels were significantly higher in both HAT and SERO TL(+) subject as compared to endemic controls (p=0.006). This result suggests that APOL1 expression is likely induced by T. b. gambiense, but is not related to resistance/susceptibility in its human host.
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