Plasmodium yoelii: influence of immune modulators on the development of the liver stage.

Plasmodium sporozoites suppress the respiratory burst and antigen presentation of Kupffer cells, which are regarded as the portal of invasion into hepatocytes. It is not known whether immune modulation of Kupffer cells can affect the liver stage. In the present study, we found that sporozoites inoculated into Wistar rats could be detected in the liver, spleen, and lung; however, most sporozoites were arrested in the liver. Sporozoites were captured by Kupffer cells lined with endothelial cells in the liver sinusoid before hepatocyte invasion. Pretreatment with TLR3 agonist poly(I:C) and TLR2 agonist BCG primarily activated Kupffer cells, inhibiting the sporozoite development into the exoerythrocytic form, whereas Kupffer cell antagonists dexamethasone and cyclophosphamide promoted development of the liver stage. Our data suggests that sporozoite development into its exoerythrocytic form may be associated with Kupffer cell functional status. Immune modulation of Kupffer cells could be a promising strategy to prevent malaria parasite infection.

Plasmodium yoelii: contribution of oocysts melanization to natural refractoriness in Anopheles dirus.

It is well known that Anopheles dirus is naturally refractory to rodent malaria parasite, Plasmodium yoelii, but the mechanism is still largely unknown. Here, we found that some P. yoelii taken into An. dirus could develop into oocysts, but oocysts were partially melanized at 7 days and completely melanized at 15 days post-infectious blood meal. Transmission electronic microscopy could find the melanized P. yoelii oocysts in An. dirus as early as 5 days post-infection, with a few haemocytes attaching to the melanized oocysts, indicating a typical humoral melanization reaction. Although the change of protein pattern at 24h post-infection suggested that other unknown mechanisms and/or factors might be involved in killing ookinetes, our data implied that oocysts melanization was one of the mechanisms of An. dirus to block P. yoelii development. In addition, activity of phenoloxidase, such as monophenol oxidase and o-diphenoloxidase, in haemolymph of An. dirus fed on infectious blood meal was much higher than that of mosquitoes fed on 5% glucose or normal mouse blood (p<0.05), implying the possible role of PO in oocysts melanization by An. dirus.

Relationship between hemolymph phenol oxidase and melanization of Plasmodium yoelii oocysts in Anopheles dirus / 第三军医大学学报

Objective　To explore the relationship between hemolymph phenol oxidase and the melanization of Plasmodium yoelii oocysts in Anopheles dirus. Methods　An Anopheles dirus-Plasmodium yoelii system was used Anopheles dirus were divided into 3 groups, that is, non-blood-fedding (N), normal-blood-fedding (B) and infected-blood-fedding (I). The activities of MPO and o-DPO in hemolymph from 3 groups were determined with native polyacrylamide gel electrophoresis (PAGE) and density scanning at 5, 7, 11 and 15 d after blood feeding. Results　Both MPO and o-DPO activity were significantly higher in group I than group N and B (P<0.05). But with the melanization of Plasmodium yoelii oocysts, both MPO and o-DPO activity in group I were decreased in comparison with group N, especially on the 15 th day after infected-blood feeding. MPO and o-DPO activity in group B were significantly stronger than those of group N. Conclusion　Blood feeding and infection of Plasmodium yoelii both can activate the cascade. The heamolymph phenol oxidase may play an important role in the melanization of Plasmodium yoelii oocysts in Anopheles dirus.

Relationship between hemolymph phenol oxidase and melanization of Plasmodium yoelii oocysts in Anopheles dirus / 第三军医大学学报

Objective　To explore the relationship between hemolymph phenol oxidase and the melanization of Plasmodium yoelii oocysts in Anopheles dirus. Methods　An Anopheles dirus-Plasmodium yoelii system was used Anopheles dirus were divided into 3 groups, that is, non-blood-fedding (N), normal-blood-fedding (B) and infected-blood-fedding (I). The activities of MPO and o-DPO in hemolymph from 3 groups were determined with native polyacrylamide gel electrophoresis (PAGE) and density scanning at 5, 7, 11 and 15 d after blood feeding. Results　Both MPO and o-DPO activity were significantly higher in group I than group N and B (P<0.05). But with the melanization of Plasmodium yoelii oocysts, both MPO and o-DPO activity in group I were decreased in comparison with group N, especially on the 15 th day after infected-blood feeding. MPO and o-DPO activity in group B were significantly stronger than those of group N. Conclusion　Blood feeding and infection of Plasmodium yoelii both can activate the cascade. The heamolymph phenol oxidase may play an important role in the melanization of Plasmodium yoelii oocysts in Anopheles dirus.