title: Pre-existing Schistosoma japonicum infection alters the immune response to Plasmodium berghei infection in C57BL/6 mice.
abstract: BACKGROUND
  Since helminths and malaria parasites are often co-endemic, it is important to clarify the immunoregulatory mechanism that occurs during the process of co-infection. A previous study confirmed that dendritic cells (DCs) are involved in the establishment and regulation of the T-cell-mediated immune response to malaria infection. In the current study, distinct response profiles for splenic DCs and regulatory T cell (Treg) responses were assessed to evaluate the effects of a pre-existing Schistosoma japonicum infection on malaria infection.
  
  
  METHODS
  Malaria parasitaemia, survival rate, brain histopathology and clinical experimental cerebral malaria (ECM) were assessed in both Plasmodium berghei ANKA-mono-infected and S. japonicum-P. berghei ANKA-co-infected mice. Cell surface/intracellular staining and flow cytometry were used to analyse the level of splenic DC subpopulations, toll-like receptors (TLRs), DC surface molecules, Tregs (CD4⁺CD25⁺Foxp3⁺), IFN-γ/IL-10-secreting Tregs, and IFN-γ⁺/IL-10⁺-Foxp3⁻CD4⁺ T cells. IFN-γ, IL-4, IL-5, IL-10 and IL-13 levels were determined in splenocyte supernatants using enzyme-linked immunosorbent assay (ELISA).
  
  
  RESULTS
  The co-infected mice had significantly higher malaria parasitaemia, compared with the mono-infected mice, on days 2, 3, 7 and 8 after P. berghei ANKA infection. Mono-infected mice had a slightly lower survival rate, while clinical ECM symptoms, and brain pathology, were significantly more severe during the period of susceptibility to ECM. On days 5 and 8 post P. berghei ANKA infection, co-infected mice had significantly lower levels of CD11c⁺CD11b⁺, CD11c⁺CD45R/B220⁺, CD11c⁺TLR4⁺, CD11c⁺TLR9⁺, CD11c⁺MHCII⁺, CD11c⁺CD86⁺, IFN-γ-secreting Tregs, and IFN-γ⁺Foxp3⁻CD4⁺ T cells in single-cell suspensions of splenocytes when compared with P. berghei ANKA-mono-infected mice. Co-infected mice also had significantly lower levels of IFN-γ and higher levels of IL-4, IL-5, and IL-13 in splenocyte supernatants compared to mono-infected mice. There were no differences in the levels of IL-10-secreting Tregs or IL-10⁺Foxp3⁻CD4⁺ T cells between co-infected and mono-infected mice.
  
  
  CONCLUSIONS
  A Tregs-associated Th2 response plays an important role in protecting against ECM pathology. Pre-existing S. japonicum infection suppressed TLR ligand-induced DC maturation and had an anti-inflammatory effect during malaria infection not only by virtue of its ability to induce Th2 responses, but also by directly suppressing the ability of DC to produce pro-inflammatory mediators.
authors.affiliation: Department of Microbiology and Parasitology, College of Basic Medical Sciences, China Medical University, No, 92 Beier Road, Heping District, Shenyang 110001, China. enjieluo@hotmail.com.
authors.forename: Mei-lian
authors.initials: ML
authors.lastname: Wang
authors.forename: Ya-ming
authors.initials: YM
authors.lastname: Cao
authors.forename: En-jie
authors.initials: EJ
authors.lastname: Luo
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
authors.forename: Ya-jun
authors.initials: YJ
authors.lastname: Guo
mesh_terms: D000818:Animals; D001921:Brain / Q000473:pathology; D003713:Dendritic Cells / Q000276:immunology; D004195:Disease Models, Animal; D005260:Female; D006651:Histocytochemistry; D007108:Immune Tolerance; D016130:Immunophenotyping; D008288:Malaria / Q000276:immunology* / Q000469:parasitology / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018512:Parasitemia / Q000469:parasitology; D010962:Plasmodium berghei / Q000276:immunology*; D012549:Schistosoma japonicum / Q000276:immunology*; D012554:Schistosomiasis japonica / Q000150:complications / Q000276:immunology* / Q000473:pathology; D013154:Spleen / Q000276:immunology; D016019:Survival Analysis; D050378:T-Lymphocytes, Regulatory / Q000276:immunology
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