Previous Article | Next Article ![]()
Clinical and Diagnostic Laboratory Immunology, September 2005, p. 1036-1040, Vol. 12, No. 9
1071-412X/05/$08.00+0 doi:10.1128/CDLI.12.9.1036-1040.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Laboratory of Clinical Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland,1 Clinical Services Program, SAIC-Frederick, Inc., NCI-Frederick, Frederick, Maryland 21702,2 The EMMES Corporation, Rockville, Maryland,3 Tulane National Primate Research Center, Tulane University Health Sciences Center, Covington, Louisiana4
Received 12 January 2005/ Returned for modification 9 May 2005/ Accepted 15 June 2005
|
|
|---|
|
|
|---|
Posttreatment Lyme disease syndrome (PTLDS) designates the condition of patients who suffer from chronic symptoms after adequate antibiotic therapy, even though evidence of a persistent infection is lacking. Common complaints include fatigue, headaches, myalgias, arthralgias, and cognitive impairment. The mechanism underlying this syndrome is unknown, and management of these patients is controversial, but antibiotic therapy appears not to be beneficial (11).
The B. burgdorferi-specific immune complex (IC) test has been used in early Lyme infection and has been suggested as a possible marker of active infection (5, 6, 16). One method uses polyethylene glycol (PEG) precipitation to isolate the IC from the serum (PEG-IC). The objective of this study was to examine the presence of B. burgdorferi-specific antibodies within serum PEG-ICs in patients with LD, patients with PTLDS, and controls and evaluate whether this test could be useful as a marker of active infection.
|
|
|---|
Controls included healthy volunteers from the area of endemicity (n = 18) and OspA vaccinees (n = 31). Both groups had no previous history compatible with LD. Healthy volunteers had a negative Western blot to B. burgdorferi in the serum by the CDC criteria. OspA vaccinees had received at least two doses of the OspA vaccine (Lymerix) before the evaluation. The OspA vaccinee group included 11 females and 20 males, with a mean age of 49 years (range, 20 to 69 years). The mean time from the last dose of the vaccine to the study sample was 6 months.
All patients and controls had negative rapid plasma reagin in serum. The study was approved by the Institutional Review Board of the National Institute of Allergy and Infectious Diseases, and all patients and controls gave written informed consent.
Monkeys. Serum samples were obtained from rhesus macaques that were chronically infected with B. burgdorferi (n = 3), uninfected (n = 10), or vaccinated with OspA (n = 7). Chronically infected animals were inoculated with the JD1 strain of B. burgdorferi as described previously (9). Blood samples were obtained at several weeks postinfection and pooled for each animal, with week 22 being the earliest collection time and week 36 the latest. OspA-vaccinated animals were given inoculations with OspA/Al(OH)3 with or without the adjuvant monophosphoryl lipid A, as described previously (13). Blood samples were obtained at 10 weeks (n = 4) and 6 weeks (n = 5) after the first vaccine dose.
PEG-IC isolation and dissociation. ICs were isolated by PEG precipitation and dissociated as previously described (4, 16). Briefly, 0.3 ml of serum was added to an equal amount of 7% PEG in 0.1 M sodium borate buffer (pH 8.4) and incubated for 2 h or overnight at 4°C. After 8,400-relative-centrifugal-force centrifugation for 10 min, the pellet was washed twice with 3.5% PEG in 0.1 M borate buffer, pH 8.4, and resuspended in 0.15 ml of 0.1 M borate buffer, pH 10.2. The elevated pH serves to dissociate the PEG-IC. Further antigen concentration was attempted for several PEG-IC preparations by neutralizing the dissociated PEG-IC with 3 M sodium acetate (pH 5.27), thereby reassociating the antigen-antibody complexes. These newly formed antigen-antibody complexes are capable of binding immunoprecipitating proteins conjugated to agarose beads as previously described (4). Briefly, to bind IgG-containing complexes, 0.1 ml of GammaBind G Sepharose (Pharmacia, Piscataway, NJ) was added to the above-mentioned neutralized PEG-IC sample, and the sample was placed on a reciprocal shaker for 1 h at 4°C. Binding of IgM complexes was attempted with the addition of 0.1 ml of mannan-binding protein (Ultralink; Pierce, Rockford, Ill.) and a similar 1-hour incubation. Protein L-agarose (Santa Cruz, CA) was then added to bind IgA and any other IgG or IgM antibodies that may not have bound to the other immunoprecipitating proteins. This antibody binding mixture was shaken overnight at 4°C and centrifuged at 8,400 relative centrifugal force for 15 min (beaded IC).
ELISA for PEG-ICs and serum antibodies to B. burgdorferi. Dissociated PEG-ICs were diluted 1:10, and unprocessed serum samples (diluted 1:100) were tested separately by IgG and IgM ELISA (MarDx, Carlsbad, Calif.), following the manufacturer's directions. ELISAs were considered to be positive when the optical density readings were greater than 3 standard deviations above the mean of at least 10 negative controls run on each plate.
Western blots. Identification of OspA from B. burgdorferi in the dissociated PEG-IC material was done by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions in either 12% or 4 to 12% precast Bis-Tris Gels with MOPS (morpholinepropanesulfonic acid) (Invitrogen Life Technologies, Carlsbad, CA). The beaded PEG-IC material was resuspended in Western blot reducing buffer, boiled to dissociate the antigens, and electrophoresed using the same precast gels. Proteins were transferred onto polyvinylidene difluoride membranes using the Pharmacia semidry Multiphor II NovaBlot (Amersham Pharmacia Biotech Inc., Piscataway, NJ) transfer apparatus. B. burgdorferi B31 sonicate (Biodesign International, Saco, ME) or recombinant OspA (provided by GlaxoSmithKline S.A., Gerval, Belgium, and John Dunn, Brookhaven National Laboratory, Upton, NY) were used as controls.
Membranes were probed using anti-OspA monoclonal antibodies H5332 (provided by Alan Barbour, University of CaliforniaIrvine, Irvine, CA) and C65550M (BioDesign International, Saco, ME), followed by peroxidase-conjugated goat anti-mouse IgG Fab-specific antibody A2304 (Sigma-Aldrich Corp., St. Louis, MO). A third anti-OspA monoclonal antibody was also used. This was MAB302 (Maine Biotechnology Services Inc., Portland, ME), biotinylated with E-Z link biotin hydrazide (Pierce Biotechnology, Inc., Rockford, IL) and detected with the Vectastain Elite ABC kit (Vector Laboratories, Inc., Burlingame, CA). This approach was introduced to avoid the need to use a secondary antibody to detect OspA. Membranes also were probed with peroxidase-conjugated rabbit polyclonal antibody against B. burgdorferi B65304P (BioDesign International, Saco, ME).
|
|
|---|
|
View this table: [in a new window] |
TABLE 1. Samples evaluated using serum and PEG-IC ELISA for the presence of anti-B. burgdorferi IgG and IgM
|
|
View this table: [in a new window] |
TABLE 2. ELISA and PEG-IC IgG and IgM results
|
|
View this table: [in a new window] |
TABLE 3. Precision values for IgG and IgM serum and PEG-IC ELISA
|
Results that were obtained with the monkey serum samples paralleled the results obtained in humans. All of the OspA-vaccinated monkey samples (n = 9) were positive by both serum IgG ELISA and PEG-IC IgG ELISA. These samples were negative for both serum IgM ELISA and PEG-IC IgM ELISA. Results obtained with serum specimens from infected monkeys (n = 3) were the same with both tests, while samples from control monkeys (n = 10) were negative in all tests.
We next addressed the question of whether serum IgG ELISA and PEG-IC IgG ELISA were independent tests. Because all but one healthy volunteer had negative serum ELISA results, we used the results from OspA vaccinees to assess the independence of the tests, as it is expected that vaccinees would have mostly (or only) free anti-OspA IgG antibody. Sixteen (52%) tested positive for serum IgG ELISA. Fourteen of the 16 samples positive by serum IgG ELISA were positive by PEG-IC IgG ELISA. Using Fisher's exact two-tailed test, we found that the frequency of positive PEG-IC IgG ELISA was significantly higher among ELISA-reactive than among ELISA-negative serum samples (P = 0.0003). The difference is also significant if the six serum samples with indeterminate ELISA results (samples that were tested twice and had different results in each test) are added to the positive samples (P = 0.001).
To address the question of concentration of immunoglobulins by the PEG-IC procedure, we measured the immunoglobulin contents of 19 serum and PEG-IC pairs by nephelometry (Beckman Array 360; Beckman Coulter, Inc., Fullerton, CA). Samples were assessed in a blinded fashion at the Clinical Pathology Laboratory of the Warren Grant Magnuson Clinical Center. The samples were prepared and diluted as described in Materials and Methods for use in the ELISA (PEG-ICs were diluted 1:10, and sera 1:100). For PEG-ICs and sera, the mean IgG values were 111.69 mg/dl and 10.3 mg/dl, while the mean IgM values were 103.82 mg/dl and 1.63 mg/dl. Taking into account the initial steps used in the preparation of the PEG-IC (where samples were actually concentrated 2:1), we calculated the total amounts of IgG and IgM by multiplying the measured values by 100 for the serum samples and by 5 for the PEG-ICs. The serum IgG and IgM mean values were 1,030 mg/dl and 163 mg/dl, while the PEG-IC IgG and IgM mean values were 558.5 mg/dl and 519 mg/dl. Therefore, the IgM values in the PEG-ICs were increased by 3.2-fold while the IgG values were 50% less than the respective serum values.
Next, we tried to detect B. burgdorferi antigen in PEG-ICs from patients with active infection by immunoprecipitation followed by immunoblot analysis for the presence of OspA, using the anti-OspA monoclonal antibodies H5332 and C65550, as well as the polyclonal anti-B. burgdorferi antibody. We observed similar banding patterns in all patient and control groups in all of the probed membranes, with between two and three bands (depending upon the gel resolution) migrating around the 31-kDa OspA migration zone. These results were present in multiple experiments, and the use of the GammaBind G Sepharose, mannan-binding protein, and protein L-agarose antibody binding beads in the antigen preparation (see Materials and Methods) failed to remove the nonspecific binding. Lowering the concentration of the primary H5332 anti-OspA monoclonal antibody from 1:10 to 1:100 did not allow any specific OspA bands to appear. The use of the biotinylated MAB302 anti-OspA antibody gave similar results. We also dissociated the PEG-ICs by using an acidic pH of 3.5 instead of the sodium acetate basic pH 10.2 buffer and tried the less reactive Western Lightning Chemiluminescence Reagent (Perkin-Elmer Life Sciences, Boston, MA) to prevent any nonspecific bands from possibly overwhelming any OspA-specific visualization, with no success. In a final attempt to obtain an OspA-specific band, proteins were transferred from the gels to the polyvinylidene difluoride membrane using a wet-transfer mode (Trans-Blot; Bio-Rad, Hercules, CA), followed by colorimetric development with TMB-1 component membrane peroxidase substrate (BioFX Laboratories, Owings Mills, MD). Using the last method, no bands, specific or nonspecific, appeared around the 31-kDa area in the PEG-IC lanes.
|
|
|---|
There are two possible explanations for our finding of the positive PEG-IC in vaccinated individuals. The most likely possibility is that the method used for the preparation of the PEG-IC precipitates not only immune-complexed antibody but also a significant quantity of free antibody. This possibility, coupled with our finding that there is a much larger amount of immunoglobulin in the PEG-IC preparations than in the unprocessed serum, as used for the ELISA (111.69 mg/dl for IgG and 103.82 mg/dl for IgM in the PEG-ICs versus 10.3 mg/dl for IgG and 1.63 mg/dl for IgM in unprocessed serum), could explain the cases when positive PEG-IC tests occur in the face of a negative serum ELISA result. It can also explain the increased sensitivity of the PEG-IC test in early disease, instead of the exclusive freeing of complexed antibody to make the antibodies in the immune complexes accessible to measurement by ELISAs, as has been hypothesized (7, 14-16). One question regarding this hypothesis is why we would have results where the serum ELISA was positive but the PEG-IC was negative. That discrepancy occurred in 3 and 12 samples with the IgG and IgM ELISAs, respectively. When examined more closely, two of the IgG samples were tested more than once, and in both, the results were different at the second analysis (one had negative serum with a positive PEG-IC, while the other had both serum and PEG-IC positive). The other sample and all the samples showing inconsistent IgM results were tested only once. It is possible that the discrepancies are due to the intralaboratory variability of the test and would be resolved by retesting these samples.
Another potential explanation for the findings of positive PEG-ICs in the vaccinated group is the production of anti-idiotype antibodies after vaccination, which would form circulating immune complexes with the anti-OspA antibodies. If this hypothesis were correct, the precipitated immunoglobulins would be part of immune complexes. As similar anti-idiotypic immune complexes could also be formed in patients after clearing of the infection, these complexes would still present a problem for the use of this test as a possible marker of infection, as precipitated antibodies would not necessarily represent antibody-antigen complex.
In conclusion, this study presents evidence contrary to the use of PEG-IC combined with standard ELISA as a marker of active infection in patients with persistent symptoms or in individuals who received the OspA vaccine.
This project has been funded in part with federal funds from the National Cancer Institute, National Institutes of Health, under contract no. NO1-CO-12400.
The content of this publication does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.
|
|
|---|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»