TABLE 1.4.

Interactions between complement and parasites in the CNS.

	Study design	Outcomes	Conclusion	References
Plasmodium
1	(Human) Proteomic analysis on the frontal lobe (autopsy) of subjects with cerebral malaria (CM) caused by Plasmodium falciparum.	(1) Proteins associated with innate immune response, complement system (C1qb), coagulation, the platelet activation, are elevated in CM. (2) Proteins associated with myelination, oxidative phosphorylation, ROS regulation, sodium and calcium ion transport are depleted in CM.	Innate immune responses (including the complement system) and associated demyelination may contribute to the severity of CM.	Kumar et al., 2018
2	(in vivo) Experimental Malaria in Pregnancy (EMIP) model using P. berghei ANKA in mice (WT vs. C5aR deficient).	(1) In utero exposure to EMIP induced persistent neurocognitive deficit and affective disorders in the offspring. (2) In utero EMIP-induced cognitive deficit in offspring was rescued by genetic or pharmacological disruption of C5aR signaling. (3) In utero EMIP-induced reduction in neurotransmitter levels (dopamine, 5-HT, and norepinephrine) was observed only in WT (not in C5aR deficient) offspring.	In utero exposure to MIP induces cognitive deficit in offspring via maternal C5aR signaling.	McDonald et al., 2015
3	(in vivo) CM model using P. berghei ANKA in mice (WT and C5 deficient).	C5 deficient mice were protected against infection-induced seizures and high spike frequency.	C5 plays a role in malaria-induced seizures.	Buckingham et al., 2014
4	(1) (in vivo) CM model using P. berghei ANKA in mice (WT, C5aR deficient, and C5L2 deficient). (2) (Human) Plasma from children presenting with CM or uncomplicated malaria (UM) (case-control)	(1) In experimental CM model, C5aR deficient mice (but not C5L2 deficient) showed (moderately) improved survival that was associated with reduced levels of proinflammatory cytokines and chemokine (TNF, IFN-g, and CCL2), as well as preserved endothelial integrity, compared to WT mice. (2) In human subjects, serum C5a levels were significantly higher in CM children compared to UM.	Dysregulated C5aR signaling contributes to the pathogenesis of CM.	Kim et al., 2014
5	(in vivo) CM model using P. berghei ANKA in mice (C57BL/6 WT, C4 deficient, FB deficient, and C3 deficient).	(1) C4 deficient and FB deficient mice were fully susceptible to CM. (2) C3 deficient mice were partially resistant to CM. (3) Terminal activation (C5 cleavage) occurred in C3 deficient mice during CM.	Terminal pathway activation during CM occurs independently of the three upstream pathways, suggesting the crosstalk between coagulation cascade and complement cascade.	Ramos et al., 2012
6	(in vivo) CM model in mice using P. berghei ANKA. Mouse strains: WT, C5 deficient, C5aR deficient, and C3aR deficient.	(1) C5 deficient mice were resistant to cerebral malaria, whereas C5aR deficient and C3aR deficient mice were susceptible. (2) C9 deposition was detected throughout the cortex of infected mice. C9 deposits frequently colocalized with blood vessels, while some were detected in the parenchyma. (3) anti-C9 antibody treatment significantly delayed the progress of cerebral malaria.	Protection of C5 deficient mice against cerebral malaria is mediated through the inhibition of MAC formation, not through C5a-induced inflammation.	Ramos et al., 2011
7	(in vivo) CM model using P. berghei ANKA in mice of different genetic backgrounds. C5-deficient: A/J, C57BL/6 with C5-defective allele from A/J, and C5-deficient B10.D2. C5-sufficient: C57BL/6, A/J with C5-sufficient allele from C57BL/6, and C5-deficient B10.D2.	(1) CM was associated with the presence of C5 gene. C5-sufficient mice were susceptible while and C5-deficient mice were CM resistant. (2) C5a and C5aR blockade rescued susceptible mice from CM.	C5 and C5a are responsible for CM pathogenesis.	Patel et al., 2008
8	(in vivo) CM model using P. berghei ANKA in mice.	Increased C1q and C5 proteins in the brain of cerebral malaria. C1q and C5 levels correlated with clinical severity.	C1q and C5 are locally upregulated in the brain in cerebral malaria.	Lackner et al., 2008
9	(in vivo) CM model using P. berghei ANKA in mice (BALB/c; nu/nu and nu/+) (in vivo)	(1) Compared to nu/+, nu/nu mice were protected against CM despite higher parasitemia. (2) Early rapid decrease in serum C3 and increase in serum immune complex levels were observed in nu/+ mice, but not in nu/nu.	T cell-deficiency is protective against CM, which was accompanied by reduced complement activation.	Finley et al., 1982
Toxoplasma gondii
	Study design	Outcomes	Conclusion	References
1	(in vivo and in vitro) Toxoplasma infection model: Type II T. gondii (Fukaya) in mice (in vivo); Type II T. gondii (PTG) in murine primary glia (in vitro)	(1) mRNA levels of C1qa, C3, FB, FP, C3aR, and C5aR were persistently up-regulated in the infected brain. (2) C5a protein was up-regulated in the infected brain. (3) Toxoplasma infection in glial cells induced the up-regulation of mRNA for C1qa, FB, FP, and C5aR in a microglia-dependent manner.	Toxoplasma infection induced the expression of the alternative pathway components (FB and FP) and anaphylatoxin receptors (C3aR and C5aR), which was partly mediated by microglia.	Shinjyo et al., 2021
2	(in vivo) Chronic Toxoplasma infection model: Type II T. gondii (Prugniaud) in mice (Kumming). Measures: proteomics using brain tissue samples.	Complement (C3, C4b, and C1qa) and coagulation (e.g., plasminogen) pathways were highly upregulated in the brain of infected mice. Tight junction pathway was disordered.	In Toxoplasma-infected brain, complement components (C3, C4b, and C1q) were upregulated possibly causing the disruption of tight junctions.	Huang et al., 2019
3	(in vivo) Persistent infection model: Type I T. gondii (GT1) in mice (5 months post infection)	(1) Complement C1q, C1r, C3, and C4 levels were elevated in the brain with high Toxoplasma cyst burden. (2) Complement proteins were deposited on the surface of degenerating neurons.	T. gondii cyst burden is associated with up-regulation of complement components (C1q, C1r, C3, and C4), which leads to complement deposition on the surface of degenerating neurons.	Li et al., 2019
4	(in vivo) Chronic Toxoplasma infection model in mice, using type I (GT1, virulent) and type II (ME49, avirulent) strains.	(1) C1q mRNA and protein levels increased after infection. C1q levels correlated with Toxoplasma cyst burden. (2) C1q expression was predominantly cytoplasmic, which was in the cells adjacent to GFAP positive astrocytes, near breached cyst barriers. (3) C1q colocalized with Toxoplasma cysts in the brain.	Toxoplasma infection causes upregulation of C1q in the brain, particularly near parasite cysts and punctate synaptic patterns.	Xiao et al., 2016

The relevant complement proteins are highlighted in bold.