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Infection and Immunity, August 1999, p. 3998-4007, Vol. 67, No. 8
Corixa Corporation1
and Infectious Disease Research
Institute,2 Seattle, Washington 98104
Received 23 February 1999/Returned for modification 14 April
1999/Accepted 27 May 1999
Culture filtrate proteins (CFP) of Mycobacterium
tuberculosis have been shown to contain immunogenic components
that elicit at least partial protective immunity against
Mycobacterium infection. To clone genes encoding some of
the immunogenic proteins, we made a high-titer rabbit anti-CFP serum
and used it to screen an M. tuberculosis genomic expression
library in Escherichia coli. In this paper, we describe the
molecular cloning of two new protein components of CFP and identified
them as members of the serine protease gene family. Their open reading
frames contain N-terminal hydrophobic secretory signals consistent with
their detection in CFP. The predicted molecular masses of the mature,
fully processed forms of both antigens are ~32 kDa, in agreement with
their observed sizes on immunoblots of CFP probed with polyclonal
rabbit antisera made to the recombinant proteins. Thus, these proteins
have been designated MTB32A and MTB32B. Interestingly, and despite 66%
amino acid sequence homology between the two proteins, polyclonal
rabbit antisera made to each of the recombinant proteins were found to be specific for the respective immunizing antigens. The recombinant proteins were also evaluated in in vitro assays with donor peripheral blood mononuclear cells (PBMC) from healthy purified protein derivative (PPD)-positive individuals of diverse ethnic backgrounds. MTB32A but
not MTB32B stimulated PBMC from healthy PPD-positive donors but not
from PPD-negative donors to proliferate and secrete gamma interferon.
MTB32A is encoded by a single-copy gene which is present in both
virulent and avirulent strains of the M. tuberculosis complex and the BCG strain of Mycobacterium bovis but
absent in the environmental mycobacterial species tested. In addition,
nucleotide sequence comparison of mtb32a of the avirulent
H37Ra strain and the virulent Erdman strain, as well as with the
corresponding sequences (identified in the databases) of strain H37Rv
and the clinical isolate CSU93, revealed 100% identity. MTB32A,
therefore, represents a candidate for inclusion in subunit vaccine
development. Finally, the possible role of MTB32 serine proteases as a
virulence factor(s) during Mycobacterium spp. infection is discussed.
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Cloning, Expression, and Immunological Evaluation
of Two Putative Secreted Serine Protease Antigens of
Mycobacterium tuberculosis
*
Corresponding author. Mailing address: Corixa
Corporation, 1124 Columbia St., Seattle, WA 98104. Phone: (206)
754-5772. Fax: (206) 754-5715. E-mail: Skeiky{at}Corixa.Com.
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