Glutathione data of Eurasian siskins either infected with avian malaria or not

Avian haemosporidian parasites are globally widespread with a broad
repertoire of hosts. When infected, the host can either reduce the
parasite burden (resistance) and/or limit the severity of parasitaemia
(tolerance). Oxidative stress is known to play a pivotal role in the
host’s resistance and tolerance as well as its detrimental endpoints. The
rationale behind this paradox lies in the dual role of reactive oxygen
species (ROS): they can have both beneficial and detrimental effects for
the host, while being largely harmful to the parasite. Thus, it is in the
parasite’s interest to maintain a reduced environment within the host’s
cell, whereas the host needs a fine-tuned balance between generating ROS
to eliminate the parasites and maintaining sufficient antioxidant levels
to protect its own tissues. This dynamic is what we refer to as the
host-parasite oxidative arms-race. In this study, Eurasian siskins (Spinus
spinus) were experimentally infected with Plasmodium ashfordi to
investigate how the fundamental antioxidant system – the glutathione
redox-system – responds to infection over time compared to control birds.
By combining physiological measures and gene expression data of key
glutathione related genes from both the parasite and the host at different
time points, we provide evidence of this oxidative arms race. The gene
expression data show that the parasite actively maintains reduced
intracellular environment and eliminates ROS through high expression of
superoxide dismutase (SOD), glutathione reductase (GR), and glutathione
synthetase. In contrast, the host upregulates glutathione S-transferases
(GSTs) and glutathione peroxidases (GPX), which reduce the physiologically
active levels of the key antioxidant, glutathione. Although, the parasite
seems to win the race in terms of the oxidative state of the cell, the
marked decrease in parasitaemia from day 21 (45%) to 31 (15%) suggests
that the host’s strategy by lowering the physiological glutathione levels
is sufficient to defeat the parasite.