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Infect. Immun. doi:10.1128/IAI.00677-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Expression, Purification and Characterization of the Immunological Response to a 40 kDa Plasmodium vivax Tryptophan-Rich Antigen (PvTRAg40)

Department of Biotechnology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi-110029, India; National Institute of Malaria Research (ICMR), Field Station, Jabalpur, (M. P.) 482003, India; National Institute of Malaria Research, 22 Shamnath Marg, Delhi 110054,India

^* To whom correspondence should be addressed. Email: ydsharma_aiims{at}yahoo.com.

	Abstract

We describe here a 40 kDa Plasmodium vivax tryptophan-rich antigen (PvTRAg40) which contains 321 amino acids and 11.4% tryptophan residues. This protein shows 65% homology (35% identity) with the previously described PvTRAg besides sharing 23 of 27 positionally conserved tryptophan residues and similar genomic organization. Nucleotide sequence of the entire tryptophan–rich domain of PvTRAg40 was identical among 35 P.vivax clinical isolates. The protein is expressed by ring, trophozoite, and schizont stages of the parasite. The cDNA covering the exon-2 of PvTRAg40 was cloned, expressed in pPROEXHTa vector and recombinant protein purified. A high humoral immune response (90.7% seropositivity, n=43) was detected in humans during the course of natural P. vivax infection against this recombinant protein. Eighty percent of the total 20 P. vivax-exposed individuals exhibited the lymphoproliferative responses against this antigen. The T-cells of these individuals were producing higher amount of IL-12, IL-4 and IL-10 than IFN-, and TNF- cytokines in response to the recombinant protein. Production of Th2 biased cytokines, conserved T and B cell epitopes and an enhanced humoral immune response indicate that PvTRAg40 could possibly induce antibody mediated immune protection against infection.