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Infection and Immunity, October 2001, p. 6456-6462, Vol. 69, No. 10
Department of Internal Medicine, Yale
University School of Medicine, New Haven, Connecticut 06520
Received 30 March 2001/Returned for modification 11 May
2001/Accepted 26 June 2001
Natural antibodies are those immunoglobulin molecules found in
mammalian serum that arise in the absence of exposure to environmental pathogens and may comprise an early host defense against invading pathogens. The spirochete Borrelia burgdorferi first
encounters natural antibodies when its arthropod vector, Ixodes
scapularis, begins feeding on a mammalian host. Natural
antibodies may therefore have an impact on pathogens within
blood-sucking vectors, prior to pathogen transmission to the mammal. In
this study, we investigated whether natural antibodies influenced the
number and/or phenotype of B. burgdorferi organisms
within feeding I. scapularis nymphs. Using a competitive
PCR, we found that ticks ingesting a blood meal from B-cell-deficient
mice, which lack all immunoglobulins, contained fivefold more
spirochete DNA than ticks feeding on control mice. Spirochete DNA
levels could be reduced to that of controls with passive transfer of
normal mouse serum or polyclonal immunoglobulin M (IgM), but not IgG,
into B-cell-deficient mice prior to placement of infected ticks. At
48 h of tick feeding, 90% of spirochetes within salivary glands
of ticks removed from B-cell-deficient mice were found by confocal
immunofluorescence microscopy to express outer surface protein A
(OspA), compared to only 5% of salivary gland spirochetes from ticks
detached from control mice. Taken together, these results show that
ingestion of natural antibodies limits the spirochete burden within
feeding ticks. Because OspA is normally downregulated when spirochetes
moved from the tick midgut to the salivary gland, our findings suggest
that OspA-expressing midgut spirochetes may be particularly susceptible
to the borrelicidal effects of these molecules.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.10.6456-6462.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Natural Antibody Affects Survival of the Spirochete
Borrelia burgdorferi within Feeding Ticks
*
Corresponding author. Mailing address: Section of
Rheumatology, Department of Internal Medicine, Yale University School
of Medicine, New Haven, CT 06520. Phone: (203) 785-7063. Fax: (203) 785-7053. E-mail: linda.bockenstedt{at}yale.edu.
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