Trypanosoma brucei Invasion and T-Cell Infiltration of the Brain Parenchyma in Experimental Sleeping Sickness: Timing and Correlation with Functional Changes

Abstract

BackgroundThe timing of Trypanosoma brucei entry into the brain parenchyma to initiate the second, meningoencephalitic stage of human African trypanosomiasis or sleeping sickness is currently debated and even parasite invasion of the neuropil has been recently questioned. Furthermore, the relationship between neurological features and disease stage are unclear, despite the important diagnostic and therapeutic implications.MethodologyUsing a rat model of chronic Trypanosoma brucei brucei infection we determined the timing of parasite and T-cell neuropil infiltration and its correlation with functional changes. Parasite DNA was detected using trypanosome-specific PCR. Body weight and sleep structure alterations represented by sleep-onset rapid eye movement (SOREM) periods, reported in human and experimental African trypanosomiasis were monitored. The presence of parasites, as well as CD4+ and CD8+ T-cells in the neuropil was assessed over time in the brain of the same animals by immunocytochemistry and quantitative analyses.Principal findingsTrypanosome DNA was present in the brain at day 6 post-infection and increased more than 15-fold by day 21. Parasites and T-cells were observed in the parenchyma from day 9 onwards. Parasites traversing blood vessel walls were observed in the hypothalamus and other brain regions. Body weight gain was reduced from day 7 onwards. SOREM episodes started in most cases early after infection, with an increase in number and duration after parasite neuroinvasion.ConclusionThese findings demonstrate invasion of the neuropil over time, after an initial interval, by parasites and lymphocytes crossing the blood-brain barrier, and show that neurological features can precede this event. The data thus challenge the current clinical and cerebrospinal fluid criteria of disease staging.

Blood signatures for second stage human African trypanosomiasis: a transcriptomic approach

“…The second phase of CNS invasion activates chemokines which promote macrophage and lymphocyte recruitment to areas where their activity might induce additional alterations [8,9]. A number of studies have been carried to understand the mechanisms of trypanosome infections and invasion of CNS, however most of these have been done in animal and in vitro blood brain barrier models [10][11][12][13]. In human T. b rhodesiense infections, immune responses have been observed through antibody assays and protein measurements [14][15][16].…”

Blood signatures for second stage Human African Trypanosomiasis: A transcriptomic approach.

“…The second phase of CNS invasion activates chemokines which promote macrophage and lymphocyte recruitment to areas where their activity might induce additional alterations [8,9]. A number of studies have been carried to understand the mechanisms of trypanosome infections and invasion of CNS, however most of these have been done in animal and in vitro blood brain barrier models [10][11][12][13]. In human T. b rhodesiense infections, immune responses have been observed through antibody assays and protein measurements [14][15][16].The limitation to this is that only stable highly abundant molecules can be measured, leaving the low and transiently expressed proteins uncaptured.…”

Sleeping Sickness: A Tale of Two Clocks

“…Curiously, although T. brucei can be observed in the CSF of patients [one of the methods to diagnose late stage of infection (WHO, 2019 )], trypanosomes do not survive for long in CSF (Wolburg et al, 2012 ). Parasites could also be crossing the BBB similarly to lymphocytes (Mulenga et al, 2001 ; Laperchia et al, 2016 ). When parasites reach the brain parenchyma they seem to concentrate in the median eminence and hypothalamic areas (Lundkvist et al, 2004 ; Rijo-Ferreira et al, 2018 ), but the brain-biogeographical and/or physiological cues parasites use remain elusive.…”