TransfectedPlasmodium knowlesiProduces Bioactive Host Gamma Interferon: a New Perspective for Modulating Immune Responses to Malaria Parasites

Abstract

Transgenic pathogenic microorganisms expressing host cytokines such as gamma interferon (IFN-␥) have been shown to manipulate host-pathogen interaction, leading to immunomodulation and enhanced protection. Expression of host cytokines in malaria parasites offers the opportunity to investigate the potential of an immunomodulatory approach by generating immunopotentiated parasites. Using the primate malaria parasite Plasmodium knowlesi, we explored the conditions for expressing host cytokines in malaria parasites. P. knowlesi parasites transfected with DNA constructs for expressing rhesus monkey (Macaca mulatta) IFN-␥ under the control of the heterologous P. berghei apical membrane antigen 1 promoter, produced bioactive IFN-␥ in a developmentally regulated manner. IFN-␥ expression had no marked effect on in vitro parasite development. Bioactivity of the parasite-produced IFN-␥ was shown through inhibition of virus cytopathic effect and confirmed by using M. mulatta peripheral blood cells in vitro. These data indicate for the first time that it is feasible to generate malaria parasites expressing bioactive host immunomodulatory cytokines. Furthermore, cytokine-expressing malaria parasites offer the opportunity to analyze cytokine-mediated modulation of malaria during the blood and liver stages of the infection.Recombinant pathogenic microorganisms expressing host cytokines such as gamma interferon (IFN-␥) have been shown to modulate immune responses, leading to enhanced protection (15-17, 19, 35, 43, 47). Vaccinia virus and simian immunodeficiency viruses expressing a range of host cytokines were attenuated in vivo, leading to enhanced immune responses (15-17), and Leishmania major expressing host IFN-␥ was significantly attenuated in nude mice (47). These data indicate that in vivo expression of host cytokines by pathogens can manipulate the host-pathogen interaction and generate protective host responses. Thus far, expression of host cytokines by malaria parasites has not been examined. The development of transfection technology for malaria parasites (18,49,51,54) now enables expression of recombinant host proteins, such as cytokines in Plasmodium.IFN-␥ is one of the central effector cytokines in host response to malaria infection, especially during the liver stage (14,21,33,(38)(39)(40) and hence is attractive for expression in malaria parasites. In vitro and in vivo studies in rodent models of malaria have demonstrated that IFN-␥ plays a central role in protection against malaria liver-stage infection, possibly by inducing the infected hepatocyte to produce nitric oxide that kills parasites (31,33). In clinical vaccination studies with an attenuated sporozoite vaccine (reviewed in reference 32), vaccinated humans were protected from subsequent infection through IFN-␥-dependent responses. In separate studies in mice and monkeys, sterile protection was achieved through IFN-␥-dependent responses after exogenous treatment with interleukin-12 (IL-12) (21, 39). Studies using rodent and human malaria models have demon...

Plasmodium-encoded murine IL-6 impairs liver stage infection and elicits long-lasting sterilizing immunity

“…Unfortunately, the authors did not examine further the infectious behavior and whether this transgenic parasite was protective or not against an infectious parasite challenge (Ozwara et al, 2003). In contrast to our present study, none of these reports could investigate the mechanisms underlying these partial protective capabilities.…”

“…With regard to other Plasmodium parasites engineered to produce host cytokines, only one early study demonstrated that transgenic P. knowlesi parasites express bioactive IFN-ψ. Unfortunately, the authors did not examine further the infectious behavior and whether this transgenic parasite was protective or not against an infectious parasite challenge [25]. In contrast to our present study, none of these reports could investigate the mechanisms underlying these partial protective capabilities.…”

Plasmodium knowlesi: a relevant, versatile experimental malaria model

“…In conclusion, the P. knowlesi transfection system is versatile, in terms of vitro-vivo shuttling, which can be essential for the detection of certain phenotypes that are not displayed in vitro (e.g. overexpression of IFN-γ (Ozwara et al 2003 a ) could have impact on host immune response), and it is highly efficient and suitable for both episomal transfection as well as single and double crossover integration into the genome.…”

Plasmodium-encoded murine IL-6 impairs liver stage infection and elicits long-lasting sterilizing immunity

“…With regard to other Plasmodium parasites engineered to produce host cytokines, only one early study demonstrated that transgenic P. knowlesi parasites express bioactive IFN-γ. Unfortunately, the authors did not examine further the infectious behavior and whether this transgenic parasite was protective or not against an infectious parasite challenge ( 29 ). In contrast to our present study, none of these reports could investigate the mechanisms underlying these partial protective capabilities.…”