Academic journal article Iranian Journal of Public Health

High-Level Expression of Immunogenic Recombinant Plasmodium Vivax Merozoite Surface Protein (Pvmsp-1 ^Sub 42^ kDa) in pGEX 6P1 Vector

Academic journal article Iranian Journal of Public Health

High-Level Expression of Immunogenic Recombinant Plasmodium Vivax Merozoite Surface Protein (Pvmsp-1 ^Sub 42^ kDa) in pGEX 6P1 Vector

Article excerpt

Introduction

Plasmodium vivax (P. vivax) is the second most frequent human malaria parasite. It has been estimated that 2.85 billion people all around the world are at risk of this infection (1). Compared to the lethal counterpart, P. falciparum, which a few months to few years after the initial blood-stage infection, the infection could be treated, P. vivax could be relapsed and expanded. It may also be cases of chloroquine resistance or severe complications. In spite of focused efforts to reduce the mortality rate caused by P. falciparum, the prevalence of P. vivax is faster than the prevalence of P. falciparum in many endemic regions (2). For the time being, although malaria-eliminating programs are performing in 25 out of 32 countries in the world, these efforts merely or chiefly are against P. vivax (3). Due to the limitation of conventional microscopy, new direct diagnostic techniques have aroused the research for immunodiagnostic methods.

Existence of the malaria parasite in the organs of patient causes the creation of an extensive range of antibodies, both specifically against Plasmodia antigens and against nonspecific cells or agents such as red blood cells, leukocytes, rheumatoid factor, etc. (4). A few days after the invasion of the parasite into the bloodstream, species-specific, stage-specific and genus specific antibodies are identifiable and may persist long after the infection has occurred. There are antibodies against all blood stages of the parasite schizogonic cycle even against exoerythrocytic schizonts, but commonly available serological tests are aimed at the detection of antibodies against asexual blood stages for applicable intentions (supply of antigen) (5). The best antigens are obviously homologous antigens (P. falciparum, P. vivax, P. ovale, P. malariae), but an adequate supply is practically accessible merely for P. falciparum, which is cultured in vitro. For the serological diagnosis of the other species of Plasmodia, heterologous antigens are to be used (P. cynomolgi for P. vivax and P. braflianum for P. malariae).

Merozoite surface protein 1 (MSP-1) is one of the most promising candidates among the antigens presently under examination in malaria vaccines and diagnostic kits (6). On the parasite surface, the MSP-1 antigen is expressed as a large protein of 190-200 kDa. During the merozoite maturation, this precursor undergoes two phases of proteolytic cleavage. First, it is separated into four great fragments of 83, 30, 38 and 42 kDa (further referred to as MSP-1 S3, MSP-130, MSP-138, and MSP-1 f, then the MSP-142 fragment undergoes a second cleavage before erythrocytic invasion which leads to the production of 33 and 19 kDa (MSP-133 and MSP-1 f fragments, while during the invasion, only MSP-119 remains on the merozoite surface (7).

Seroepidemiology of malaria is evaluated by detection of antibodies using ELISA. Flowever, regarding P. vivax, the difficulty of blood stage cultivation has prevented the use of this methodology. Making recombinant proteins via the methods of genetic engineering can provide adequate P. vivax blood stage antigens for the foundation of specific serological assays. Regarding the use of recombinant proteins established upon the sequence of the merozoite surface protein-1 (MSP-1) of P. vivax in the series of immuno-epidemiological studies, we inferred that, carboxy-terminal region of MSP-1 recombinant protein was highly immunogenic that was recognized by antibodies of persons who was lately exposed to P. vivax (8). In addition, the carboxy-terminal region of MSP-1 gene from P. vivax exhibits restricted polymorphism alleles (especially MSP-119) in various regions of the world, which does not restrict recognition by human antibodies (9, 10). Subsequently, these results suggest that it could be possible to develop serological tests using recombinant proteins based on the P. vivax carboxy-terminal 42 kDa region of MSP-1. This recombinant protein can be used in malaria serological diagnostic tests such as ELISA after serologic evaluation explained above. …

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