Abstract
BackgroundRegulatory T cells are known to play a key role to counter balance the protective immune response and immune mediated pathology. However, the role of naturally occurring regulatory cells CD4+CD25+Foxp3+ in malaria infection during the disease pathogenesis is controversial. Beside this, ICOS molecule has been shown to be involved in the development and function of regulatory T cell enhance IL-10 production. Therefore, possible involvement of the ICOS dependent regulatory CD4+ICOS+Foxp3+ T cells in resistance/susceptibility during malaria parasite is explored in this study.Methods5 × 105 red blood cells infected with non-lethal and lethal parasites were inoculated in female Balb/c mice by intra-peritoneal injection. Infected or uninfected mice were sacrificed at early (3rd day post infection) and later stage (10th day post infection) of infection. Harvested cells were analysed by using flow cytometer and serum cytokine by Bioplex assay.ResultsThin blood films show that percentages of parasitaemia increases with disease progression in infections with the lethal malaria parasite and mice eventually die by day 14th post-infection. Whereas in case of non-lethal malaria parasite, parasitaemia goes down by 7th day post infection and gets cleared within 13th day. The number of CD4+ ICOS+ T cells increases in lethal infection with disease progression. Surprisingly, in non-lethal parasite, ICOS expression decreases after day 7th post infection as parasitaemia goes down. The frequency of CD4+ICOS+FoxP3+ Tregs was significantly higher in lethal parasitic infection as compared to the non-lethal parasite. The level of IL-12 cytokine was remarkably higher in non-lethal infection compared to the lethal infection. In contrast, the level of IL-10 cytokines was higher in lethal parasite infection compared to the non-lethal parasite.ConclusionTaken together, these data suggest that lethal parasite induce immunosuppressive environment, protecting from host immune responses and help the parasite to survive whereas non-lethal parasite leads to low frequencies of Treg cells seldom impede immune response that allow the parasite to get self-resolved.Graphical
Highlights
Regulatory T cells are known to play a key role to counter balance the protective immune response and immune mediated pathology
Parasitaemia and survival To determine the mode of infectivity of Plasmodium species: P. berghei and P. chabaudi in vivo, BALB/c mice were used and infected with 5 × 105 syngeneic parasitized erythrocytes by intra-peritoneal (i.p.)
It was observed that animals infected with P. berghei exhibited gradual increase in parasitaemia till they die on 13–14th day post infection
Summary
Regulatory T cells are known to play a key role to counter balance the protective immune response and immune mediated pathology. The role of naturally occurring regulatory cells C D4+CD25+Foxp3+ in malaria infection during the disease pathogenesis is controversial. Possible involvement of the ICOS dependent regulatory CD4+ICOS+Foxp3+ T cells in resistance/susceptibility during malaria parasite is explored in this study. Even though success of various public health measures made, malaria is still a challenging disease in developing countries like South East Asia, South America and Africa [4]. Malaria disease is characterized by inflammation and massive infiltration of immune cells in spleen resulting into splenomegaly [5]. It is well reported that blood-stage infection with rodent parasites, such as Plasmodium yoelii, Plasmodium berghei and Plasmodium chabaudi induce potent inflammatory response and leads to various manifestations of experimental malaria [8]
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