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Infection and Immunity, November 2001, p. 6853-6862, Vol. 69, No. 11
Program in Vector-Borne Diseases, Department
of Veterinary Microbiology and Pathology, Washington State University,
Pullman, Washington 99164,1 and
Department of Animal Sciences, University of Illinois,
Urbana-Champaign, Illinois 618012
Received 9 May 2001/Returned for modification 7 July 2001/Accepted 29 July 2001
Native major surface protein 1 (MSP1) of the ehrlichial pathogen
Anaplasma marginale induces protective immunity in calves challenged with homologous and heterologous strains. MSP1 is a heteromeric complex of a single MSP1a protein covalently associated with MSP1b polypeptides, of which at least two (designated MSP1F1 and
MSP1F3) in the Florida strain are expressed. Immunization with
recombinant MSP1a and MSP1b alone or in combination fails to provide
protection. The protective immunity in calves immunized with native
MSP1 is associated with the development of opsonizing and neutralizing
antibodies, but CD4+ T-lymphocyte responses have not been
evaluated. CD4+ T lymphocytes participate in protective
immunity to ehrlichial pathogens through production of gamma
interferon (IFN-
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.11.6853-6862.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
CD4+ T Lymphocytes from Calves Immunized with
Anaplasma marginale Major Surface Protein 1 (MSP1), a
Heteromeric Complex of MSP1a and MSP1b, Preferentially Recognize the
MSP1a Carboxyl Terminus That Is Conserved among Strains
), which promotes switching to high-affinity
immunoglobulin G (IgG) and activation of phagocytic cells to produce
nitric oxide. Thus, an effective vaccine for A. marginale
and related organisms should contain both T- and B-lymphocyte epitopes
that induce a strong memory response that can be recalled upon
challenge with homologous and heterologous strains. This study was
designed to determine the relative contributions of MSP1a and MSP1b
proteins, which contain both variant and conserved amino acid
sequences, in stimulating memory CD4+ T-lymphocyte
responses in calves immunized with native MSP1. Peripheral blood
mononuclear cells and CD4+ T-cell lines from MSP1-immunized
calves proliferated vigorously in response to the immunizing strain
(Florida) and heterologous strains of A. marginale. The
conserved MSP1-specific response was preferentially directed to the
carboxyl-terminal region of MSP1a, which stimulated high levels of
IFN-
production by CD4+ T cells. In contrast, there was
either weak or no recognition of MSP1b proteins. Paradoxically, all
calves developed high titers of IgG antibodies to both MSP1a and MSP1b
polypeptides. These findings suggest that in calves immunized with MSP1
heteromeric complex, MSP1a-specific T lymphocytes may provide help to
MSP1b-specific B lymphocytes. The data provide a basis for determining
whether selected MSP1a CD4+ T-lymphocyte epitopes and
selected MSP1a and MSP1b B-lymphocyte epitopes presented on the same
molecule can stimulate a protective immune response.
*
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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