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Infection and Immunity, November 2003, p. 6338-6343, Vol. 71, No. 11
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.11.6338-6343.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

PPE Antigen Rv2430c of Mycobacterium tuberculosis Induces a Strong B-Cell Response

Rakesh Kumar Choudhary,1 Sangita Mukhopadhyay,1 Prachee Chakhaiyar,1 Naresh Sharma,1 K. J. R. Murthy,2 V. M. Katoch,3 and Seyed E. Hasnain1,4*

Centre for DNA Fingerprinting and Diagnostics, Hyderabad 500-076,1 Immunology Unit, Mahavir Hospital and Research Centre, A. C. Guards, Hyderabad 500-004,2 Central Jalma Institute of Leprosy, Tajganj, Agra 282-001,3 Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560-064, India4

Received 8 April 2003/ Returned for modification 20 May 2003/ Accepted 8 August 2003

The variation in sequence and length in the C-terminal region among members of the unique PE (Pro-Glu) and PPE (Pro-Pro-Glu) protein families of Mycobacterium tuberculosis is a likely source of antigenic variation, giving rise to the speculation that these protein families could be immunologically important. Based on in silico analysis, we selected a hypothetical open reading frame (ORF) encoding a protein belonging to the PPE family and having epitopes with predictably higher antigenic indexes. Reverse transcriptase PCR using total RNA extracted from in vitro-cultured M. tuberculosis H37Rv generated an mRNA product corresponding to this gene, indicating the expression of this ORF (Rv2430c) at the mRNA level. Recombinant protein expressed in Escherichia coli was used to screen the sera of M. tuberculosis-infected patients, as well as those of clinically healthy controls (n = 10), by enzyme-linked immunosorbent assay. The panel of patient sera comprised sera from fresh infection cases (category 1; n = 32), patients with relapsed tuberculosis (category 2; n = 30), and extrapulmonary cases (category 3; n = 30). Category 2 and 3 sera had strong antibody responses to the PPE antigen, equal to or higher than those to other well-known antigens, such as Hsp10 or purified protein derivative (PPD). However, a higher percentage of patients belonging to category 1, as opposed to clinically healthy controls, showed stronger antibody response against the PPE protein when probed with anti-immunoglobulin M (IgM) (71 versus 37.5%) or anti-IgG (62.5 versus 28.12%). Our results reveal that this PPE ORF induces a strong B-cell response compared to that generated by M. tuberculosis Hsp10 or PPD, pointing to the immunodominant nature of the protein.

* Corresponding author. Mailing address: C.D.F.D., ECIL Rd., Nacharam, Hyderabad 500-076, India. Fax: 91-040 27155610 and 91-040 27155479. Phone: 91-040 27155604 and 91-040 27155605. E-mail: hasnain{at}cdfd.org.in.

Editor: J. M. Mansfield

Infection and Immunity, November 2003, p. 6338-6343, Vol. 71, No. 11
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.11.6338-6343.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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