Exposições prévias a parasitos vivos de plasmodium berghei nk65 na proteção contra a malária cerebral experimental

Abstract

Malaria remains a great world health issue. The occurrence of Plasmodium species and strains with different degrees of virulence in one area makes its essential to clarify the mechanism of immune response in the host during malarial infections. This elucidation can collaborate in strategies that avoids the disease severity or even the infection. So, this study aims to investigate the occurrence of transcendent antimalarial immune response in pre-exposed mice to live parasites of Plasmodium berghei NK65 (PbN) and challenged with P. berghei ANKA (PbA). First, we determined the concentration of parasites that were capable to induce cerebral malaria (CM) in C57BL/6 mice. For that, 105 , 106 e 5x106 parasitized erythrocytes (pRBCs) were tested, all groups presented low levels of parasitaemia, decreased clinical score and death between the period estimated for the development of cerebral malaria. In front of the parameter linearity shown by the group that received 105 parasitized erythrocytes, that was the inoculum used in the experiments. So, C57BL/6 mice were exposed once or twice to 103 parasitized erythrocytes by PbN. Following 30, 90 and 180 days after the last exposure to parasites, animals were challenged with 105 pRBCs by PbA. Then, animals were daily followed since day 4 after infection to determine the clinical score, parasitaemia and survival rate. Antibody levels, histopathological findings at cerebral tissue, cerebral cytokine levels, splenic index, splenocytes phenotype and T CD4+ , CD8+ and B cerebral lymphocyte population were also evaluated. We could observe that, in average, 21% of pre-exposed animals once or twice to PbA and 43% and 54% of animals pre-exposed to PbN, respectively, did not developed CM. Interestingly, survival rate and parasitaemia levels remained similar when challenge was performed 90 days after the last exposure, on the other hand, protection declined to 20% in animals challenged 180 days after the last exposure. IgG1, IgG2a, IgG2b and IgG3 levels showed similar between animals that developed CM and those that were protected from the severe form of the disease, even in animals that were challenged 30, 90 and 180 days after the last pre-exposition. TNF-α e IFN-Ɣ pro-inflammatory and IL-10 antiinflammatory cytokine analysis shown similar levels between pre-exposed groups and the group that was not infected, independently of the type of immunization or the clinical profile showed by animals, or even the elapsed time until the challenge (30, 90 or 180 days). Regarding the splenocytes phenotyping, when animals were challenged 30 days after the last exposure, they showed low frequencies of B lymphocytes, naïve B cells or cytotoxic T cells when did not developed CM, compared to the control group or to animals that developed the severe form of the disease. Then, pre-expositions to low virulence live parasites influences at the experimental cerebral malaria development in murine model caused by PbA.