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Infection and Immunity, December 2003, p. 7211-7214, Vol. 71, No. 12
0019-9567/03/$08.00+0 DOI: 10.1128/IAI.71.12.7211-7214.2003
Copyright © 2003, American
Society for
Microbiology. All Rights Reserved.
Immunogenicity of Borrelia burgdorferi Arthritis-Related Protein
Sunlian Feng, Emir Hodzic, Kimberly Freet, and Stephen W. Barthold*
Center
for Comparative Medicine, Schools of Medicine and Veterinary Medicine,
University of California at Davis, Davis, California
95616
Received 30 May 2003/
Returned for modification 16 July 2003/
Accepted 2 September 2003
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ABSTRACT
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Immunization
against arthritis-related protein (Arp) elicits antibody in mice that
resolves arthritis but is not protective against challenge with
Borrelia burgdorferi. In mice immunized against Arp, an
unrelated 37-kDa protein (P37-42), outer surface protein A (OspA), or
glutathione S-transferase (GT) and then challenged by syringe
or tick, only OspA conferred protection. Passive transfer of Arp
antiserum into infected SCID mice induced arthritis resolution, but
antisera to P37-42, OspA, GT, or six overlapping Arp peptide fragments
did not. Results suggest that the arthritis-resolving immunogenicity is
specific to Arp, but the relevant epitopes may be
conformational.
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TEXT
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The agent of Lyme disease, Borrelia burgdorferi, disseminates
in mice following syringe- or tick-borne infection,resulting in induction of arthritis and carditis, which then undergo
immune-mediated resolution
(1,
2,
3). Although disease
resolves, infection persists and the infected mice develop strong
protective and disease-resolving antibody responses, which can be
measured by passive transfer. Transfer of immune serum from infected
immunocompetent mice into naïve mice protects against syringe
challenge with B. burgdorferi but not against tick
challenge or against host-adapted spirochetes
(4,
5,
7). Passive transfer of
immune serum into SCID mice with existing infection also induces
arthritis resolution but does not eliminate infection, thus mimicking
events in immunocompetent mice
(4,
5,
6).
Two proteins
illustrate the concept that different antigenic targets may be involved
in protective or arthritis-resolving immunity. Decorin binding protein
A (DbpA) elicits protective immunity against syringe (but not
tick)-borne challenge
(10,
14-16,
18), yet does not induce
disease-resolving immunity
(10). In contrast,
arthritis-related protein (Arp) elicits arthritis-resolving immunity
but not protective immunity against syringe-borne challenge
(9). Since these negative
findings with syringe challenge could be attributed to the fact that
Arp is expressed in vivo rather than under culture conditions and
expression increases within ticks during feeding
(17), a more thorough
examination of protective immunity using both syringe and tick
challenges was undertaken. The immunogenicity of Arp was compared to
that induced by glutathione S-transferase (GT, negative
control), P37-42 (similar-size protein, negative control), and OspA
(positive control).
The arp gene, lacking the
hydrophobic N-terminal leader region (amino acids 1 to 12), was
amplified by PCR with oligonucleotide primers
(9). Primers corresponded
with nucleotides 37 to 73 and 951 to 975 of the arp gene
(GenBank sequence accession no.
N40-AF050212),
which is nearly identical to B31 sequence bbf01
(13). Amplicons were
cloned in frame with the GT gene into pMX, a pGEX-2T vector (Pharmacia,
Piscataway, N.J.) with a modified polylinker
(18). Recombinant P37-42
(GenBank sequence accession no.
N40-AF035553),
which is nearly identical to B31 open reading frame bbk47, was
also generated without the leader peptide, by using primers
corresponding with nucleotides 72 to 98 and 953 to 987
(9,
13). The PCR-amplified
DNA sequences were confirmed by sequence comparison with the original
insert. Recombinant proteins were purified free of their GT fusion
partner as described previously
(8). OspA was generated
from Escherichia coli transformed with plasmid 197-OspA-N40
(11), which was provided
by Erol Fikrig, Yale University School of Medicine. OspA was purified
and cleaved of its GT fusion partner as described above.
Female
C3H/HeN (Harlan Sprague-Dawley, Inc., Indianapolis, Ind.) mice were
hyperimmunized subcutaneously with 20 µg of purified
recombinant protein emulsified in 0.1 ml of complete Freund's
adjuvant and boosted at 14 and 28 days with 10 µg of protein in
incomplete Freund's adjuvant. To confirm effective immunization,
mice were bled 2 weeks after the last boost, sera were tested by
enzyme-linked immunosorbent assay with the respective recombinant
proteins, and antibody reactivity was verified at serum dilutions of
1:100,000 (10).
Groups of 10 C3H mice were immunized with Arp, P37-42 (negative
control), OspA (positive control), and GT (negative control). Five mice
in each group were then challenged intradermally in the dorsal thoracic
midline with a clonal isolate of B. burgdorferi cN40,
at a dose of 104 spirochetes in 0.1 ml of modified
Barbour-Stoenner-Kelly medium
(3), or with five
B. burgdorferi cN40-infected nymphal Ixodes
scapularis lymphal ticks placed on the thoracic dorsal midline.
Adult ticks were field collected in southern Connecticut by Durland
Fish, Yale University, New Haven, Conn. Infections were induced by
feeding larval ticks upon experimentally infected mice, and infection
status of nymphal ticks was verified as previously described
(17). Mice were killed 2
weeks after challenge, and then urinary bladder and inoculation sites
were cultured to determine infection status.
Only the mice
immunized with OspA, and not with Arp, P37-42, or GT, were protected
against challenge by syringe or tick (Table
1), confirming the effectiveness of the immunization protocol (OspA) but
the nonprotective ability of Arp immunization. Furthermore, there were
no significant differences in copy numbers of spirochetes in the ear,
tibiotarsus, or heart among the infected groups of mice, regardless of
mode of infection (Fig.
1 and 2). For quantitative
analysis, ear, heart base, and left tibiotarsal tissues were analyzed,
and copy numbers of flaB DNA target were expressed per unit
weight
of tissue (17). Multiple
comparison analyses were made using one-way analysis of variance,
followed by least squares difference post hoc tests. Calculated
P values of <0.05 were considered significant.
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TABLE 1. Evaluation
of protective immunity in C3H mice actively immunized with different
recombinant proteins and challenged with syringe- or tick-borne B.
burgdorferi
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FIG. 1. Numbers
of B. burgdorferi flaB gene copies per milligram of
ear, heart, or tibiotarsal joint tissue at 2 weeks after syringe
challenge with B. burgdorferi in mice previously
immunized with GT, Arp, OspA, or P37-42. Other than the OspA
positive-control group, there were no differences in copy numbers among
treatment groups compared with GT or P37-42 negative
controls.
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FIG. 2. Numbers
of B. burgdorferi flaB gene copies per milligram of
ear, heart, or tibiotarsal joint tissue at 2 weeks after tick challenge
with B. burgdorferi in mice previously immunized with
Arp, OspA, or P37-42. Other than the OspA positive-control group, there
were no differences in copy numbers among treatment groups compared
with P37-42 negative
controls.
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A
previous study demonstrated that passive transfer of antiserum to Arp
would induce resolution of arthritis in infected SCID mice
(9), but a truncated form
of Arp (ErpT), which is 50 amino acids shorter than Arp at the C
terminus, did not induce arthritis-resolving immunity
(12). Based upon this
fact, we sought to confirm the lack of activity with truncated Arp and
to attempt to identify the immunogenic region of Arp by creating
overlapping polypeptide fragments, using methods described above. A
series of six Arp peptide fragments were created (Fig.
3): ArpFr1, amino acids 13 to 194; ArpFr2, amino acids 145 to 326; ArpFr3,
amino acids 13 to 94; ArpFr4, amino acids 60 to 326; ArpFr5, amino
acids 13 to 281; and ArpFr6, amino acids 240 to 326. Immunoblots of
full-length Arp and each of the six Arp fragments were incubated with
serum from C3H mice that were actively infected with B.
burgdorferi for 90 days and with hyperimmune serum prepared
against each recombinant Arp. Immune serum reacted with Arp and ArpFr4
but not with ArpFr1, ArpFr2, ArpFr3, ArpFr5, or ArpFr6. Hyperimmune
serum against Arp reacted with Arp, ArpFr1, ArpFr2, ArpFr4, and ArpFr5
but not ArpFr3 or ArpFr6, the two smallest peptide fragments (data not
shown).

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FIG. 3. Relative
size and relationships of full-length and fragments of arp
gene sequences encoding Arp (ca. 35 kDa), ArpFr1 (ca. 20 kDa), ArpFr2
(ca. 20 kDa), ArpFr3 (ca. 9 kDa), ArpFr4 (ca. 30 kDa), ArpFr5 (ca. 30
kDa), and ArpFr6 (ca. 10
kDa).
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We next generated hyperimmune antisera to Arp, P37-42,
OspA, GT, and each of the six Arp peptide fragments and then tested
these antisera for their ability to induce arthritis resolution
following passive transfer into infected female
C3H/Smn.CIcrHsd-Prkdcscid (C3H-scid) mice
obtained from the Frederick Cancer Research Center, Frederick, Md. At 6
and 10 days after intradermal inoculation with 103
spirochetes (intervals at which arthritis is established and evolving),
groups of four C3H-scid mice were injected subcutaneously with
0.3 ml of antisera to Arp, ArpFr1 to ArpFr6 peptide fragments, OspA,
P37-42, or GT. Because of the number of mice needed to execute this
experiment, up to four antisera were tested in a single experiment, but
each experiment contained a group of GT antiserum-treated controls.
Mice were necropsied 2 weeks later, tissues were cultured to confirm
infection status, and tissues (joints and hearts) were examined by
histology. Both knees and tibiotarsi from each mouse were examined for
the presence of arthritis, and tibiotarsi were scored by blinded
examination for arthritis on a scale of 0 (negative) to 3 (severe)
(5,
6).
Compared to
control mice treated with GT antiserum (mean severity score, 2.7
± 0.4), no effect on arthritis was noted with OspA antiserum
(mean severity score, 2.4 ± 0.6) or P37-42 antiserum (mean
severity score, 2.6 ± 0.9), whereas Arp antiserum resulted in
reduction of arthritis severity (mean severity score, 1.1 ±
0.3). None of the antisera to ArpFr1 through ArpFr6 caused arthritis
resolution in passively immunized C3H-scid mice (data not
shown). Furthermore, active immunization of C3H mice with these
recombinant proteins did not induce protective immunity (data not
shown).
The present study confirms previous findings that
immunization with recombinant Arp elicits an antibody response that
will reduce the severity of arthritis in actively infected SCID mice
upon passive transfer (9).
Furthermore, we found that antiserum generated against peptide
fragments of Arp did not have this quality, which explains why ErpT, a
truncated form of Arp, failed to induce arthritis-resolving immunity
(12). Results suggest
that the arthritis-resolving immunogenicity of the recombinant protein
is likely to be conformational. In studies with recombinant OspC, it
has been shown that the conformational nature of the recombinant
protein is critically important in eliciting therapeutic immunity in
SCID mice infected with B. burgdorferi ZS7
(20,
21), and the
immunogenicity of DbpA has likewise been linked to conformational
structure (19).
Arp
serves as a prototype antigen to study host immune responses to an in
vivo-expressed antigen that elicits disease-modulating responses during
active infection. Although the biological activity and function of Arp
have yet to be defined, it is presumably important to B.
burgdorferi, as B. burgdorferi B31 encodes a
gene product that is identical to that of B.
burgdorferi N40 Arp on the protein level
(9,
13). In addition,
B. bissetti 25015, B. afzelii PKo,
and B. garinii PBi all possess this gene and express
Arp protein as well
(9).
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ACKNOWLEDGMENTS
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We thank Sara Mulinyawe and Amy Smith for technical
support.
This work was supported by NIH grant AI26815 from the
National Institute of Allergy and Infectious
Diseases.
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FOOTNOTES
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* Corresponding
author. Mailing address: Center for Comparative Medicine, University of
California at Davis, One Shields Ave., Davis, CA 95616. Phone: (530)
752-1245. Fax: (530) 752-7914. E-mail:
swbarthold{at}ucdavis.edu. 
Editor:
F. C. Fang
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Infection and Immunity, December 2003, p. 7211-7214, Vol. 71, No. 12
0019-9567/03/$08.00+0 DOI: 10.1128/IAI.71.12.7211-7214.2003
Copyright © 2003, American
Society for
Microbiology. All Rights Reserved.
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