Induction of nitric oxide synthase protects against malaria in mice exposed to irradiated Plasmodium berghei infected mosquitoes: involvement of interferon gamma and CD8+ T cells.

Abstract

SummaryExposure of BALB/c mice to mosquitoes infected with irradiated Plasmodium berghei confers protective immunity against subsequent sporozoite challenge. Immunized mice challenged with viable sporozoites develop parasitemia when treated orally with substrate inhibitors of nitric oxide synthase (NOS). This suggests that the production of nitric oxide (NO) prevents the development of exoerythrocytic stages of malaria in liver. Liver tissue from immunized mice expressed maximal levels of mKNA for inducible NOS (iNOS) between 12 and 24 h after challenge with sporozoites. Intraperitoneal injection of neutralizing monoclonal antibody against interferon 3/(IFN-3') or in vivo depletion of CD8 + T cells, but not CD4 + T cells, at the time of challenge blocked expression of iNOS mlLNA and ablated protection in immunized mice. These results show that both CD8 § T cells and IFN-~/are important components in the regulation of iNOS in liver which contributes to the protective response of mice immunized with irradiated malaria sporozoites. IFN-3,, likely provided by malaria-specific CD8 + T cells, induces liver cells, hepatocytes and/or Kupffer cells, to produce NO for the destruction of infected hepatocytes or the parasite within these cells. W ithin minutes after an infected Anopheles mosquito bites the vertebrate host, malaria sporozoites migrate to the liver and invade hepatocytes. There, the parasite matures, and after several days the infected hepatocytes lyse, releasing thousands of merozoites. Once in circulation, the parasite infects erythrocytes causing parasitemia. Prior exposure to irradiated sporozoites confers protective immunity (1, 2). This immunity is directed against liver stage malaria, and does not protect against the blood stage malaria.CD8 + T cells and IFN-3' are required for protective immunity to sporozoite challenge. In vivo depletion of CD8 § T cells or neutralization of IFN-3~ blocks induction of effector activity at the hepatic stage, resulting in parasitaemia (3-5). In vitro studies show that IFN-qr kills parasites by stimulating malaria-infected hepatocytes to produce nitric oxide (NO), and the addition of monomethyl-r-arginine (NGMMLA), a substrate inhibitor of nitric oxide synthase (NOS), to primary cultures of mouse hepatocytes reversed the antiparasitic effects of IFN-'y (6, 7). Human hepatocytes also respond to IFN-3' for NO production (8). As to whether human hepatocytes exhibit antimalaria activity when stimulated to produce NO, remains to be examined.At present, the antimalaria effector mechanism triggered by sporozoites in immunized animals is not fully understood. Presumably malaria-specific CD8 + T cells act directly against infected hepatocytes by recognizing malaria antigen on the cell surface (i.e., induction of CTLs) or malaria-specific lymphocytes release cytokines, such as IFN-3,, upon parasite stimulation, which induces an antimalarial response (3)(4)(5)(9)(10)(11)(12). The relationship between CD8 + T cells, IFN-% and NO-mediated protection in sporozoite-immunized mice was ...

Impact of Recombinant Adenovirus Serotype 35 Priming versus Boosting of aPlasmodium falciparumProtein: Characterization of T- and B-Cell Responses to Liver-Stage Antigen 1

“…While antibodies have been correlated with protection from infection with the malaria parasite (25,27), T cells are believed to play a critical role in the elimination of liver-stage parasites and protection against the disease (29,36). Studies with mice indicate that a major mechanism of protection against liver-stage malaria is the production of IFN-␥ by activated CD8 ϩ T cells, which induces infected hepatocytes to synthesize nitric oxide, a molecule with a potent antiparasitic activity (8,13,50,51).…”

The Dendritic Cell-Specific Chemokine, Dendritic Cell-Derived CC Chemokine 1, Enhances Protective Cell-Mediated Immunity to Murine Malaria

“…CD8 ϩ T cells secreting IFN-␥ have been shown to be the main mediators of protection against the liver stages of murine malaria (8,13). Given the probable involvement of DC-CK1 in promoting the generation of primary T cell responses, we sought to determine whether exogenously administered DC-CK1 could enhance primary antimalaria T cell responses.…”

ASSOCIATION OF INTERFERON-γ RESPONSES TO PRE-ERYTHROCYTIC STAGE VACCINE CANDIDATE ANTIGENS OF PLASMODIUM FALCIPARUM IN YOUNG KENYAN CHILDREN WITH IMPROVED HEMOGLOBIN LEVELS: XV. ASEMBO BAY COHORT PROJECT

“…Earlier studies in animal models reported that interferon-␥ (IFN-␥) is active against infected hepatocytes and that IFN-␥ produced by CD8 + CTLs induced the infected hepatocytes to produce L-arginine-derived nitrogen oxides toxic to the intracellular parasites. [11][12][13] A recent study in BALB/c mice provided evidence that the immunity induced by immunization with irradiated sporozoites or DNA vaccines was initiated by parasite-specific CD8 + T cells and was dependent on the production of IFN-␥ and interleukin-12 (IL-12). 14 Another study in mice using multiple malaria CD8 + T cell epitope vaccine formulations also showed that protection correlated with high levels of IFN-␥-secreting cells.…”