Humoral Immune Responses to a Recombinant Plasmodium vivax Tryptophan-Rich Antigen Among Plasmodium vivax-Infected Patients and Its Localization in the Parasite

• Published in: Applied biochemistry and biotechnology Vol. 175; no. 4; pp. 2166 - 2177
• Main Authors: Siddiqui, Asim A, Khan, Fozia, Sharma, Yagya D
• Format: Journal Article
• Language: English
• Published: Boston Springer-Verlag 01.02.2015; Springer US; Springer Nature B.V
• Subjects: absorbance; Adult; Amino Acid Sequence; Animals; Antibodies, Protozoan - blood; Antigens; Antigens, Protozoan - chemistry; Antigens, Protozoan - genetics; Antigens, Protozoan - immunology; Biochemistry; Biotechnology; Chemistry; Chemistry and Materials Science; Conserved Sequence; enzyme-linked immunosorbent assay; Erythrocytes; Erythrocytes - immunology; Erythrocytes - parasitology; Female; fluorescent antibody technique; Gene Expression; Humans; humoral immunity; Immune Sera - chemistry; Immune system; Immunity, Cellular; Immunity, Humoral; Malaria; Malaria, Vivax - immunology; Malaria, Vivax - parasitology; Male; Middle Aged; Molecular Sequence Data; Parasites; patients; Plasmodium falciparum; Plasmodium falciparum - chemistry; Plasmodium falciparum - immunology; Plasmodium vivax; Plasmodium vivax - chemistry; Plasmodium vivax - immunology; Plasmodium yoelii; Plasmodium yoelii - chemistry; Plasmodium yoelii - immunology; Proteins; Protozoan Proteins - chemistry; Protozoan Proteins - genetics; Protozoan Proteins - immunology; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - immunology; sequence analysis; seroprevalence; tryptophan; Tryptophan - metabolism; Vaccines; Vector-borne diseases; Western blotting; Conserved sequence; Immunofluorescence; Electron microscopy; Malaria vaccine; Tryptophan-rich antigen
• DOI: 10.1007/s12010-014-1428-7
• ISSN: 0273-2289; 1559-0291

Our recent studies have focused on the identification and characterization of the tryptophan-rich proteins of the Plasmodium vivax parasite where their role in the elicitation of humoral and cellular responses and erythrocyte-binding activity was investigated. Here, we report the humoral responses of a 32.4-kDa P. vivax tryptophan-rich antigen (PvTRAg32.4) among the sera of P. vivax-infected patients. PvTRAg32.4 also contains an unusually high percentage of tryptophan residues (10.7 %) that are positionally conserved with its orthologues in Plasmodium yoelii (PypAg1 and PypAg2) and Plasmodium falciparum (PfTryThrA and PfMATRA). Thirty-four of the 40 (85.0 %) P. vivax isolates showed seropositivity to recombinant PvTRAg32.4 by ELISA. The mean ± SD values of optical density (OD) for P. vivax subjects and naïve individuals were 1.02 ± 0.36 and 0.26 ± 0.11, respectively. In the Western blot analysis, majority of the subjects studied (n = 44) showed reactivity to the recombinant, purified PvTRAg32.4. This antigen does not show binding to the erythrocytes, but the immunofluorescence data reveals that it is expressed in the erythrocytic stages of the parasite. Sequence analysis of the clinical isolates from various parts of the country shows that PvTRAg32.4 is highly conserved. Functional in-depth characterization of more such type of novel proteins in the parasite is warranted for the development of successful malaria intervention methods.