In order to develop tools for an early serodiagnosis of Plasmodium falciparum infection, we evaluated the usefulness of P. falciparum liver stage antigen-3 (LSA-3) as a serodiagnostic antigen. A portion of LSA-3 gene was cloned, and its recombinant protein (rLSA-3) was expressed in Escherichia coli and purified by column chromatography. The purified rLSA-3 and 120 test blood/serum samples collected from inhabitants in malaria-endemic areas of Mandalay, Myanmar were used for this study. In microscopic examinations of blood samples, P. falciparum positive rate was 39.1% (47/120) in thin smear trials, and 33.3% (40/120) in thick smear trials. Although the positive rate associated with the rLSA-3 (30.8%) was lower than that of the blood stage antigens (70.8%), rLSA-3 based enzyme-linked immunosorbent assay could detect 12 seropositive cases (10.0%), in which blood stage antigens were not detected. These results indicate that the LSA-3 is a useful antigen for an early serodiagnosis of P. falciparum infection.
Recombinant Proteins/biosynthesis/genetics/*immunology ; Plasmodium vivax/isolation & purification ; Plasmodium falciparum/*immunology ; Molecular Sequence Data ; Malaria, Falciparum/blood/*diagnosis ; Humans ; Genes, Protozoan/genetics/immunology ; Fluorescent Antibody Technique, Direct/methods ; Escherichia coli/genetics ; Enzyme-Linked Immunosorbent Assay/methods ; Early Diagnosis ; DNA, Protozoan/chemistry ; DNA Primers/chemistry ; Cloning, Molecular/methods ; Base Sequence ; Antigens, Protozoan/biosynthesis/chemistry/genetics/*immunology ; Animals ; Amino Acid Sequence

Malaria is still a major health problem in Thailand and its incidence is currently rising in Korea. To identify a useful antigen for the diagnosis of malaria patients, a cDNA expression library from malaria parasites was constructed and screened out immunologically. One clone was selected in view of its predominant reactivity with the patient sera. The recombinant malaria parasite antigen (Pv30) with 27 kDa as a C-terminal His-tag fusion protein that was produced in Escherichia coli was identified through immunoblot analysis. The deduced amino acid sequence had the sequence homology with the merozoite surface protein 1 (MSP1) genes of Plasmodium falciparum and P. yoelii, each by 41% and 42%, respectively. Measurement of serum IgG and IgM antibody to Pv30 by enzyme-linked immunosorbent assay (ELISA) was evaluated as a serodiagnostic test for malaria patients in Thailand (endemic area) and Korea (recently reemerging area). The sensitivity of P. vivax, P. falciparum, and P. malariae was 96.3% (26 /27), 90.6% (29/32), and 100% (6/6), respectively, and the specificity was 63.5% (40/63) in Thailand samples. The sensitivity of P. vivax was 98.8% (88/89), and the specificity was 96.6% (86/89) in Korean samples. Pv30 appears to be a good and reliable recombinant antigen for serodiagonosis of malaria in a nonendemic area.
Amino Acid Sequence ; Animals ; Antibodies, Protozoan ; Enzyme-Linked Immunosorbent Assay/*methods ; Human ; Korea ; Malaria, Vivax/*diagnosis/immunology ; Merozoite Surface Protein 1/*analysis/genetics/immunology ; Molecular Sequence Data ; Plasmodium vivax/chemistry/immunology/*isolation & purification ; Sensitivity and Specificity ; Serologic Tests ; Support, Non-U.S. Gov't