[toggle_content title=”Abstract”] Helminth infections such as filariasis can be life long due to immunomodulatory mechanisms elicited by the worms that prevent their elimination by the human host. Malaria prevalence is frequently high in areas where filarial nematode infections are endemic, originating co-infections. It is still an ongoing debate the extent to which worms can alter anti-plasmodial responses in a concomitantly infected host. In order to dissect the interactions occurring between both parasites, a murine model using the filarial nematode,
Litomosoides sigmodontis, and the malaria parasite,
Plasmodium berghei, ANKA in BALB/c and C57BL/6 mice has been established in the present work. One third of helminth-infected BALB/c mice remained malaria negative and did not develop detectable parasitaemia after co-infection with plasmodial sporozoites. Such outcomes were not observed after co-infection with blood stage parasites, thereby circumventing the plasmodial liver stage, but were only originated after sporozoite inoculation. Protection depended on IL-10, since IL-10 deficient co-infected mice were fully susceptible to sporozoite challenge. However, systemic IL-10 levels were low, suggesting a local function of this cytokine. 44 h after
P. berghei sporozoite inoculation increased CD8+ T cell numbers were found in the liver and spleen of co-infected mice. Interestingly, protection as well as numbers of CD8+ T cells correlated with the presence of microfilaraemia. Since microfilariae are potent stimulators of immune responses, their presence in the blood may enhance cross-protective responses against incoming sporozoites. Co-infected C57BL/6 mice showed significantly reduced cerebral malaria (CM) rates. CD8+ T cell recruitment to brain, a critical condition for CM development, was reduced in co-infected mice. Furthermore, in contrast to
P. berghei single-infected animals, groups of double infected mice presented high levels of circulating IL-10. The absolute requirement for IL-10 in CM protection was demonstrated by the total susceptibility to the pathology in IL-10 KO co-infected mice. Hence IL-10-dependent immunoregulatory mechanisms elicited by filarial nematodes might be able to suppress the overwhelming inflammatory reaction usually triggered against malaria parasites by C57BL/6 mice, preventing full progress to CM. Taken together, this work shows that depending on the genetic background different mechanisms elicited by filarial worms improve control of both liver and blood stages of concomitant malaria parasites, and moreover ameliorate severe pathology in a murine model. The main beneficial effects driven by filariae rely on IL-10, which on the one hand prevents CM through immunomodulation but on the other enhances protective anti-malarial responses in the liver. Worm eradication programs are currently being carried out in endemic countries, but this study suggests that their implementation may cause unpredictable consequences on malaria control. [/toggle_content]
[toggle_content title=”Clodronate Liposome Parameters”] [custom_table]
| Clodronate Concentration |
Total Lipid Concentration |
Lipid Composition |
Lipid Mole % |
Liposome Type |
Control Liposomes |
| 5 mg/ml1 |
23.5 mg/ml |
EPC/Chol |
86/14 |
MLV |
none |
1Author states clodronate liposome concentration as 250 mg/ml, however it is well-known that this is not achievable for clodronate liposomes. Since the liposomes were provided by the van Rooijen lab, we assume that they have the usual reported concentration of 5 mg/ml and were prepared by the usual method used by that lab.
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[toggle_content title=”Animals and Dosing”] [custom_table]
| Animal Description |
Clodronate Dose |
Dosing Method/Site |
Target Phagocytes |
Systemic Dosing? |
Systemic Results |
| BALB/c mice |
200 µl |
intrapleural |
Gr1highF4/80high pleural macrophages |
yes (i.v.) |
not evaluated |
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[toggle_content title=”Notes”]
- No details on the intrapleural dosing technique published.
- Author states that 200 µl were dosed both intrapleurally and intravenously for 4 consecutive days to “L. sigmodontis co-infected mice” without specifying the time of clodronate treatment relative to infection or data collection.
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[toggle_content title=”Results”]
- The author concluded, after FACS analysis of cells isolated from the pleural cavity, that the Gr1high+, F4/80high+ cell population which disappeared in clodronate-liposome-treated animals were macrophages.
- We did not find any reports of experiments investigating the effects of macrophage depletion in any models elsewhere in this thesis.
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