Plasmodium knowlesi circumsporozoite protein: genetic characterisation and predicted antigenicity of the central repeat region

@#Circumsporozoite protein (CSP) central repeat region is one of the main target regions of the RTS,S/AS01 vaccine for falciparum infection as it consists of immunodominant B cell epitopes. However, there is a lack of study for P. knowlesi CSP central repeat region. This study aims to characterise the CSP repeat motifs of P. knowlesi isolates in Peninsular Malaysia. CSP repeat motifs of 64 P. knowlesi isolates were identified using Rapid Automatic Detection and Alignment of Repeats (RADAR). Antigenicity of the repeat motifs and linear B cell epitopes were predicted using VaxiJen 2.0, BepiPred-2.0 and BCPred, respectively. A total of 35 dominant repeat motifs were identified. The repeat motif “AGQPQAQGDGANAGQPQAQGDGAN” has the highest repeat frequency (n=15) and antigenicity index of 1.7986. All the repeat regions were predicted as B cell epitopes. In silico approaches revealed that all repeat motifs were antigenic and consisted of B cell epitopes which could be designed as knowlesi malaria vaccine.

Cloning, expression and purification of Plasmodium knowlesi circumsporozoite protein and immunoblot analysis with P. knowlesi strain A1H1 protein extract

@#Circumsporozoite protein (CSP) is a sporozoite major surface protein of Plasmodium species. The protein showed promising protection level as a vaccine candidate against Plasmodium falciparum infection. There is a lack of studies on P. knowlesi CSP (PkCSP) as a vaccine candidate due to the high polymorphic characteristic of central repeat region. Recent studies showed the protein has a relatively conserved region at the C-terminal, which consists of T- and B-cell epitopes. This could be the target region for vaccine development against the pre-erythrocytic stage of the parasite. In this study, recombinant PkCSP was expressed using Escherichia coli system. Recombinant PkCSP was immunized in animal models and the antiserum was evaluated using immunoblot analysis. Results showed that PkCSP can be successfully expressed using the bacterial system. Endpoint titre of the antiserum were ranged up to 1:819200. Immunoblot analysis showed the antiserum recognized recombinant PkCSP but not total protein extract from P. knowlesi erythrocytic stage. In conclusion, PkCSP could elicit strong immune response in animal models. However, serum antibodies could not recognize protein from the parasite’s erythrocytic stage extract indicating it is not expressed at the erythrocytic stage. Therefore, PkCSP remains as a potential pre-erythrocytic vaccine candidate against P. knowlesi infection.

Complications of Sub-microscopic Plasmodium vivax Malaria among Orang Asli in Pos Lenjang, Kuala Lipis

@#In recent years, increasing cases of Plasmodium vivax complications had been reported all over the world. This former benign Plasmodium species is now recognized to be one of the human malaria parasites that can produce severe disease. In this article, we report two cases of sub-microscopic P. vivax malaria confirmed by PCR. Both patients were asymptomatic before treatment. They showed unusual presentations few days after initiation of antimalarial treatment. Both patients had subsequently completed antimalarial treatment and recovered completely.