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1 From the Helsinki University Eye Hospital; the 2 Department of Virology, Haartman Institute, University of Helsinki; the 3 Division of Rheumatology, Department of Medicine, Helsinki University Central Hospital; and the 4 Vaccine Development Laboratory, National Public Health Institute, Helsinki, Finland.
| Abstract |
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METHODS. Altogether 64 patients with previous AAU were examined at the Helsinki University Eye Hospital from September through December 1999. Serum specimens from the patients and sex- and age-matched healthy control subjects were tested for antibodies to C. pneumoniae and C. trachomatis by a specific microimmunofluorescence test and for antibodies to Cpn Hsp60 by enzyme immunoassay (EIA).
RESULTS. The prevalence of antibodies to C. pneumoniae (69% vs. 72%) and C. trachomatis (11% vs. 6%) did not differ significantly between the patients and control subjects, nor did the level of IgG antibodies to Cpn Hsp60 (median EIA unit, 65 vs. 48). The levels of IgA antibodies to Cpn Hsp60 were significantly higher in the patients with AAU than in the control subjects (median EIA unit, 18 vs. 10; two-tailed Wilcoxon signed rank test, P = 0.0001).
CONCLUSIONS. The high frequency of IgA antibodies to Cpn Hsp60 in patients with past AAU indicates that such patients may have persisting or recurrent infections due to C. pneumoniae. This finding suggests that C. pneumoniae may play a role in the pathogenesis of AAU.
| Introduction |
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The chlamydial heat shock protein (Hsp60) belongs to a group of proteins that are highly conserved among both prokaryotes and eukaryotes. Chlamydial Hsp60 has been suggested to play an important role in the immunopathogenesis of chlamydial infections. An aberrant immune response to chlamydial Hsp60 has been observed in several studies that have involved a complicated course after chlamydial infection. High-titer antibody to chlamydial Hsp60 has been correlated with pelvic inflammatory disease (PID), tubal infertility, and ectopic pregnancy.20 21 22 23 In addition, perihepatitis has been correlated with the presence of antibody to chlamydial Hsp60 in women who undergo laparoscopy in relation to suspected PID.24
AAU is recurrent, and its inflammatory activity varies. In spite of the known associations with infections caused by gram-negative bacteria, it is uncommon to find evidence of an infectious origin.15 Therefore, we decided to determine whether patients with AAU have evidence of previous infections due to C. pneumoniae or C. trachomatis and whether they would show an aberrant immune response to the chlamydial Hsp60 present in C. pneumoniae (Cpn Hsp60). We analyzed the presence and level of antibody titer to C. pneumoniae, C. trachomatis, and Cpn Hsp60 and compared the results with samples from sex- and age-matched healthy control subjects.
| Patients and Methods |
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Antibodies specific for C. pneumoniae were measured by the microimmunofluorescence (MIF)25 test, using purified elementary bodies of the Finnish epidemic isolate Kajaani-6 as the antigen. Sera were tested in serial fourfold dilutions from 1:32 for IgG antibodies and screened for IgM and IgA antibodies in a 1:16 dilution with fluorescein isothiocyanateconjugated anti-human Ig. All the initially IgM- and IgA-positive serum samples were absorbed with IgG removal reagent (Gullsorb; Gull Laboratories, Salt Lake City, UT) and retested in the MIF assay in serial dilutions. An antibody titer of 1:512 or more in the IgG fraction, 1:16 or more in the IgM fraction, or 1:160 or more in the IgA fraction was considered to be an indicator of an ongoing infection with C. pneumoniae, and a titer of 1:32 to 1:256 for IgG was considered to indicate previous infection due to C. pneumoniae. C. trachomatis antibodies were also studied by MIF.26 The cut points for ongoing or previous infection from C. trachomatis were the same as for C. pneumoniae.
Antibodies to C. pneumoniae and human Hsp60 were measured by
an enzyme immunoassay (EIA). Polystyrene 96-well plates (Nalge Ltd.,
Hereford, UK) were coated with recombinant Cpn Hsp60, produced in
Bacillus subtilis27
(5 µg/ml) with C-terminal
His6-tag and human Hsp60 (Sigma, St. Louis,
MO) overnight at room temperature. Residual binding was blocked by
incubation with 3% bovine serum albumin (BSA). Sera diluted 1:100 in
phosphate-buffered saline containing 1% BSA were allowed to bind to
the wells. The plates were washed, and the binding was detected with
horseradish-peroxidaselabeled antibody to human IgG (Cpn Hsp60) and
IgA (Cpn Hsp60, human Hsp60; Dako A/S, Glostrup, Denmark). After the
washing, the substrate (BM Blue POD substrate; Boehringer Mannheim,
Mannheim, Germany) was added, and the absorbance was measured at 450
nm. The results were expressed as EIA units, calculated by multiplying
the optical densities by 100. Values above the mean +2 SDs of the
control subjects (
19.7 EIA units) were considered suggestive of
previous exposure to C. pneumoniae.
This study was approved by the ethics committee of the Helsinki University Medical Faculty and the Helsinki University Central Hospital and was conducted according to the tenets of the Declaration of Helsinki. Informed consent was obtained from all the patients and control subjects.
Proportional data were compared by using the geometrical mean test (GMT), the paired comparison was performed with the Wilcoxon signed rank test, and the continuous variables were compared by using the Mann-Whitney test. No adjustment was made for multiple testing.
| Results |
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The prevalence (69% vs. 72%) and the levels (GMT, 66.8 vs. 37.2) of IgG antibodies to C. pneumoniae were similar in the patients and the control subjects (two-tailed Mann-Whitney test, P = 0.699). In addition, the prevalence of IgG antibodies (5% vs. 6%) and the levels of IgG titer (GMT, 16.7 vs. 17.3) to C. trachomatis did not differ between the patients and the control subjects.
Thirty-nine percent of the patients with AAU and 3% of the control subjects had titer of IgA antibodies to Cpn Hsp60. The levels of IgA antibodies to Cpn Hsp60 were significantly higher in the patients with AAU than in the control subjects (median EIA units, 18 vs. 10; two-tailed Wilcoxon signed rank test, P = 0.0001; Fig. 1 ). However, no statistically significant difference was observed between the patients and control subjects in the presence of IgG antibodies to Cpn Hsp60. The median EIA unit of IgG antibodies was 65 in the patients and 48 in the control subjects (Fig. 2) . The HLA-B27positive control subjects could not be distinguished from the HLA-B27negative ones in level of IgA antibodies to Cpn Hsp60 (two tailed Mann-Whitney test, P = 0.863).
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19.7 EIA units) had serologic evidence of previous
infection with C. pneumoniae. When tested for antibodies
against human Hsp60, neither the patients nor the control subjects had
marked levels of IgA antibodies (data not shown). The HLA-B27
positivity, number of recurrences, presence of fibrin exudates, chronic
course of the disease, and ankylosing spondylitis or other
spondyloarthropathy were evenly distributed among the patients with a
positive and negative titer of IgA antibodies to Cpn Hsp60. In
contrast, ocular complications, (46% vs. 15%; two tailed Mann-Whitney
test, P = 0.007) were observed more often in the former
group (Table 1) .
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| Discussion |
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When patients with a positive or negative titer of IgA antibodies to Cpn Hsp60 were evaluated, complications were more often evident in the former group. When the complications were analyzed in detail, cataract, cystoid macular degeneration, and the involvement of the posterior part of the eye were more frequent among the patients with positive IgA antibodies to Cpn Hsp60. In addition, the complications tended to affect the same eye, although the number of patients was too small for any statistical conclusions to be drawn. Of interest, Peeling et al.22 showed that antibodies to chlamydial Hsp60 in C. trachomatis infections increase the risk for PID. Although we have previously shown that C. pneumoniae is one of the triggering agents in reactive arthritis,16 in our present study, we did not observe any statistically significant difference in the distribution of ankylosing spondylitis or other spondyloarthropathies with respect to the presence or absence of IgA antibodies to Cpn Hsp60. This result is in agreement with the findings of Wakefield and Penny,29 who showed that patients with AU, with and without associated rheumatic disease, do not differ in cell-mediated response to Chlamydia-specific antigen or antibody response.
Hsps are highly conserved in evolution. It has been proposed that antibodies that have developed to Hsp during bacterial infection or T lymphocytes activated by Hsp can trigger an autoimmune reaction through molecular mimicry of host cells.30 Especially in intracellular bacterial infections, the pathogen enters a hostile environment and causes the regulation of its Hsp production to increase.31 The production of chlamydial Hsp60 is increased in cases of persistent infection.32 Evidence suggests that chlamydial Hsp60 can be a causal factor in the immunopathogenesis of various complications induced by persistent infections.21 22 23 24 33
On the basis of the evidence, it could be argued that antibodies to chlamydial Hsp60 can represent a marker for autoimmune responses to self-Hsp60 initiated through molecular mimicry.34 Among women with ectopic pregnancy in association with C. trachomatis infection, Yi et al.35 found that antibodies to chlamydial Hsp60 cross-react with peptide epitopes from human Hsp60. In our study, however, the levels of IgA antibodies to human Hsp60 were low in both the patients and control subjects. This finding suggests that the marked levels of IgA antibodies to Cpn Hsp60 were a real indicator of ongoing immune reaction caused by C. pneumoniae infection. The association of IgA responses with the patients with the worst ocular manifestations may reflect greater loads of persistent infection at mucosal surfaces such as the lung. The question also arises of whether our assay distinguishes Cpn Hsp60 from C. trachomatis Hsp60. Both Hsp60s are partly homologous. Thus, an infection by either C. pneumoniae or C. trachomatis would induce an antibody response to shared antigens of these agents, including an antibody response to Hsps. Because our patients did not have any marked serologic evidence of previous C. trachomatis infection but had evidence of C. pneumoniae infection, we reasoned that the antibody response to Cpn Hsp60 also would be specific to C. pneumoniae infection.
We conclude that the high frequency of antibodies to Cpn Hsp60 in patients with a history of AAU could indicate that the patients have persistent or recurrent infections due to C. pneumoniae. We suggest that C. pneumoniae may play a role in the pathogenesis of AAU and result in a complicated outcome.
| Footnotes |
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Submitted for publication October 27, 2000; revised March 3, 2001; accepted March 14, 2001.
Commercial relationships policy: N.
The publication costs of this article were defrayed in part by page
charge payment. This article must therefore be marked
"advertisement" in accordance with 18 U.S.C.
1734
solely to indicate this fact.
Corresponding author: Minna Huhtinen, Helsinki University Eye Hospital, PO Box 220, FIN-00029 HUS, Helsinki, Finland. minna.huhtinen{at}hus.fi
| References |
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hlberg, TH, Toivanen, A, Granfors, K, Tennant, C. (1990) Serologic evidence of Yersinia infection in patients with anterior uveitis Arch Ophthalmol 108,219-221[Abstract]
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