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Infection and Immunity, November 1998, p. 5423-5432, Vol. 66, No. 11
Department of Veterinary Microbiology and
Pathology, College of Veterinary Medicine, Washington State University,
Pullman, Washington 99164,1 and
Department of Veterinary Pathobiology, College of
Veterinary Medicine, University of Missouri, Columbia, Missouri
652112
Received 3 April 1998/Returned for modification 29 May
1998/Accepted 10 August 1998
DNAs from bacteria and variety of nonvertebrate organisms,
including nematodes, mollusks, yeasts, and insects, cause polyclonal activation of murine B lymphocytes. Similar studies have not been reported for bovine B cells, and to date no studies have reported mitogenic properties of protozoal DNA for any species. However, we and
others have observed that protozoal parasite antigens can induce the
proliferation of lymphocytes from nonexposed donors. Extending these
studies, we now show that the mitogenic property of protozoal antigen
preparations is in part attributable to parasite DNA and that
Babesia bovis DNA is directly mitogenic for bovine B cells.
DNase treatment of B. bovis extracts abrogated B. bovis-induced proliferation of peripheral blood mononuclear cells
from nonexposed cattle. Like DNAs from other organisms that were
mitogenic for murine B cells, B. bovis DNA is largely
nonmethylated and induced a dose-dependent proliferation of bovine B
cells, which was reduced upon methylation. Furthermore, B. bovis and E. coli DNAs enhanced immunoglobulin
secretion by cultured B cells, inducing moderate increases in
immunoglobulin G1 and stronger increases in immunoglobulin G2. Because
certain nonmethylated CpG motifs present in bacterial DNA are known to
stimulate proliferation of murine and human B cells, an 11-kb fragment
of B. bovis DNA was analyzed for CG dinucleotide content
and for the presence of known immunostimulatory sequences (ISS)
centered on a CG motif. The frequency of CG dinucleotides was
approximately one-half of the expected frequency, and several CpG
hexameric sequences with known activity for murine B cells were
identified. An oligodeoxynucleotide containing one of these ISS
(AACGTT), which is present within the rhoptry-associated
protein-1 (rap-1) open reading frame, was shown to
stimulate B-cell proliferation. These ISS may be involved in host
immune modulation during protozoal infection and may be useful as
vaccine adjuvants.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
DNA and a CpG Oligonucleotide Derived from
Babesia bovis Are Mitogenic for Bovine B Cells
*
Corresponding author. Mailing address: Department of
Veterinary Microbiology and Pathology, Washington State University,
Pullman, WA 99164-7040. Phone: (509) 335-6067. Fax: (509) 335-8529. E-mail: wbrown{at}vetmed.wsu.edu.
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