Evaluation by enzyme-linked immunosorbent assay of IgG anti-D and IgG subclass concentrations in immunoglobulin preparations

BACKGROUND: Anti-D immunoglobulin preparations are injected to prevent hemolytic disease of the newborn. The concentration of IgG anti-D in these preparations is usually determined by an automated hemagglutination technique using as a reference a calibrated preparation of anti-D, but the method requires special equipment and cannot be routinely applied to measure the IgG subclasses of anti-D in these preparations. STUDY DESIGN AND METHODS:Taking advantage of a recently described enzyme-linked immunosorbent assay (ELISA) for the determination of the anti-D concentration in sera of alloimmunized pregnant women, IgG anti-D and IgG subclass concentrations were measured in the international reference preparation (IRP) coded 68/419, 10 anti-D immunoglobulin preparations, and sera of 15 D-immunized volunteers. RESULTS: An IgG anti-D concentration of 61.5 +/- 4.8 microg per ampoule (mean +/- SD) was found by ELISA in IRP 68/419.This result was in agreement with previous determinations obtained by radioimmunoassay (60 microg/ampoule). The IgG subclass concentration of anti-D in this preparation was 48.4 microg of IgG1 (78.6%), 3.0 microg of IgG2 (4.8%), 9.7 microg of IgG3 (15.8%), and 0.4 microg of IgG4 (0.7%). The mean proportion of IgG subclasses of anti-D in 10 immunoglobulin preparations was similar (81.7% for IgG1, 5.0% for IgG2, 12.7% for IgG3, and 0.6% for IgG4). In the sera of 15 immunized volunteers, the IgG anti-D concentration varied from 3.1 to 68.4 microg per mL. The mean IgG subclass composition of anti-D was 79.3 percent for IgG1, 2.2 percent for IgG2, 18.1 percent for IgG3, and 0.4 percent for IgG4. The proportions of IgG3 anti-D in these sera were found to range between 1 percent and 87 percent, as in the sera of D-alloimmunized pregnant women. CONCLUSION: ELISA provides an alternative to the radioimmunoassay and the automated hemagglutination technique. In addition, it allows the evaluation of the absolute concentration of each IgG subclass of anti-D in immunoglobulin preparations and necessitates only the conventional equipment required for an immunoenzymatic assay.     

Human heterophilic antibodies display specificity for murine IgG subclasses

OBJECTIVES: The study investigated heterophilic antibodies: the human immunoglobulin classes involved and their specificity for different murine IgG subclasses. DESIGN AND METHODS: Using immunofluorometric assays for human IgA, IgM and IgG binding murine IgG1, we analyzed 173 samples displaying positive interference and 97 negative control samples from a previous study. We also set up assays for heterophilic antibody interference using Mabs from different murine IgG subclasses. Three Mabs each of murine IgG1, IgG2a and IgG2b subclasses, one murine IgG3 Mab and one rat Mab were used. RESULTS: Elevated levels of human murine IgG1-binding immunoglobulins of IgM class only were found in 40% of interference-positive samples, human IgG only in 1.7%, and human IgA only in 2.3% of the samples. Both elevated human IgG and IgM classes were found in 3.5% of the samples, IgA and IgM in 4.0%, and finally, all three immunoglobulin classes in 1.7% of the samples. Eighty percent of interference positive samples showed heterophilic assay interference for at least one murine IgG1 Mab, 35% for IgG2a, 66% for IgG2b, 52% for IgG3a and 17% for the rat Mab. CONCLUSIONS: Heterophilic antibody interference is mainly caused by IgM class human antibodies with a marked murine IgG subclass specificity. Combining assay antibodies from different murine IgG subclasses may reduce interference in immunoassays.     

An autoanalyzer test to determine immunoglobulin class and IgG subclass of blood group antibodies

An automated antiglobulin test was used to characterize the immunoglobulin class and IgG subclass of red blood cell-bound antibodies. Immunoglobulin classes and IgG subclasses of some clinically significant antibodies (anti-D and anti-CD, anti-Fy, anti- Jka) as well as of clinically insignificant anti-Chido antibodies were determined. Eighteen anti-Duffy antibodies were structurally homogeneous, and were mostly composed only of IgG1. Of the 16 anti-Fya antibodies studied only three had IgG2, and four had IgM molecules. Ten anti-Jka antibodies were heterogeneous, but all samples were either IgG1 or IgG3, or both. The most prominent immunoglobulin of 12 hyperimmune anti-Rh (anti-D and anti-CD) antibodies was IgG1. Under the conditions of our test, we also detected IgG3 and very low concentrations of IgG2 and IgG4 molecules in the anti-Rh antibodies.     

Monoclonal antibody-based solid-phase immunoenzymometric assays for quantifying human immunoglobulin G and its subclasses in serum

We developed quantitative immunoenzymometric assays for human IgG and its subclasses by using monoclonal antibodies, an avidin-biotin detection system and, as the calibrant, the U.S. National Reference Preparation for Specific Human Proteins. The assays are sensitive (detecting as little as 6 micrograms/L), precise (average inter-assay CV less than 11%), and vary linearly with concentrations over a five- to 10-fold range, depending on the monoclonal antibody. We evaluated 22 different monoclonal antibodies, many of which remained highly reactive when immobilized in wells of microtiter plates coated with bovine serum albumin-glutaraldehyde to "capture" total IgG or subclasses of IgG in the sample. We demonstrated the specificity of the most reactive antibodies by using a panel of 20 purified myeloma proteins. The sum of IgG subclass concentrations correlated well (r = 0.84, p less than 0.001) with the total IgG measured in sera from 63 apparently healthy adults (26 men, 37 women). We estimated 95 percentile reference intervals for the immunoglobulins in these subjects and determined the following mean percentage distributions of IgG subclasses: IgG1 49, IgG2 33, IgG3 9, and IgG4 7. The availability of these assays should facilitate studies of the clinical significance of the subclasses.     

Anti-Fab antibodies in humans. Predominance of minor immunoglobulin G subclasses in rheumatoid arthritis

Isoelectric focusing analyses of sera from patients with rheumatoid arthritis (RA) demonstrate two populations of antibodies directed against the Fab portion of pooled human IgG. One population is composed of polyclonal alkaline anti-Fab antibodies (alpha FABA) and the other, acidic alpha FABA which are more clonally restricted. In this study we have identified the immunoglobulin classes and subclasses of these antibodies in RA sera. Enzyme-linked immunosorbent assays (ELISA) demonstrated alpha FABA in RA sera to be predominantly IgG. A large portion of IgG alpha FABA existed as immune complexes, inasmuch as dialysis of RA sera against 6 M urea before ELISA analysis was necessary for maximal detection of alpha FABA activity. Chromatofocusing of RA sera isolated alpha FABA of different charges and revealed the acidic clonally restricted alpha FABA to be IgG4 and IgG3, whereas the polyclonal alkaline group contained IgG1, IgG2, and IgG3. Overall, acidic IgG3 and IgG4 comprised 70% of IgG alpha FABA, and high levels of IgG4 were seen in most RA sera. When alpha FABA were elevated in normal sera, they were primarily of the IgG4 subclass, and also existed as immune complexes. Serum anti-Fab activity was removed by adsorption of sera with Fab fragments. Anti-Fab antibodies of both kappa and lambda light-chain types were present in RA sera, and F(ab')2 fragments of RA serum immunoglobulin were found to possess anti-Fab activity. These studies indicate that alpha FABA in RA sera are limited to the IgG class, and that most of these antibodies exist as immune complexes and display clonal and minor IgG subclass restriction.     

IgG1 and IgG3 anti-D in maternal serum and on the RBCs of infants suffering from HDN: relationship with the severity of the disease

BACKGROUND: Anti-D IgG antibodies that are responsible for severe cases of HDN belong chiefly to IgG1 and IgG3 subclasses. The relationship between the concentrations of IgG1 anti-D and IgG3 anti-D in maternal serum and the amount bound to the surface of infants' RBCs is not known. In addition, the contribution of the two subclasses to the severity of HDN is not well established. STUDY DESIGN AND METHODS: Blood samples from 40 infants suffering from severe forms of HDN due to anti-D were collected before transfusion together with sera from their respective mother. The amount of total anti-D IgG as well as IgG1 anti-D and IgG3 anti-D on infants' RBCs and the concentration in maternal sera were determined by ELISA. RESULTS: The median percentages of IgG1 anti-D and of IgG3 anti-D in maternal sera were 90 and 10 percent, respectively, whereas on infants' RBCs they were 97 and 3 percent, respectively. The differences between maternal and infantile percentages were significant (p < 0.001). IgG1 and IgG3 anti-D bound to infants' RBCs increased concomitantly with the concentration of IgG1 and IgG3 anti-D in maternal sera. The severity of HDN correlated positively with the concentration of IgG1 anti-D in maternal sera, but negatively with the amount of IgG3 anti-D bound to infants' RBCs. In addition, the existence of a high proportion of IgG3 anti-D in maternal serum was associated with a delayed risk of fetal anemia. CONCLUSION: The proportion of IgG3 anti-D relative to the total anti-D IgG on infants' RBCs is only one- third of the proportion present in maternal serum. The study of the correlations between the amount of IgG1 anti-D and IgG3 anti-D and the severity of HDN suggests that IgG1 anti-D are more important than IgG3 anti-D in the pathogenesis of fetal anemia.     

An enzyme-linked immunosorbent assay for the quantitation of IgG anti-D and IgG subclasses in the sera of alloimmunized patients

BACKGROUND: IgG subclass composition of maternal alloantibodies to the D antigen seems to play a role in the severity of hemolytic disease of the newborn.The subclassing of IgG anti-D is usually performed by hemagglutination techniques, but the results are not quantitative and sometimes are difficult to interpret. Thus, there is a need for quantitative methods. STUDY DESIGN AND METHODS: The aim of this study was to develop an enzyme-linked immunosorbent assay (ELISA) for the quantitation of specific IgG anti-D and IgG subclasses in the sera of alloimmunized patients. Group O R1R2 red cells were sensitized with anti-D. Red cell membranes were solubilized with nonionic detergent. IgG and IgG subclasses were measured by a sensitive and reproducible immunocapture ELISA. A serum calibrated for its IgG subclass content was used as a reference, and the anti-D preparation 68/419 was used as an internal control. Optimal conditions for the detection of IgG anti-D and IgG subclasses by ELISA were studied. The absolute concentration and the proportions of IgG subclasses were determined in the sera of 14 pregnant women. RESULTS: A close parallelism was observed between dilutions of the IgG reference serum and the IgG anti-D solubilized from sensitized RBCs. The sum of IgG anti-D subclass concentrations, determined by the ELISA, correlated well with other quantitative methods. CONCLUSION: The method described is sensitive and can be used routinely for the quantitative determination of specific IgG anti-D and IgG subclasses in sera.     

Comparison of IgG subclasses and complement binding activity of autoantibodies from patients with bullous pemphigoid and pemphigus

Bullous pemphigoid and pemphigus are autoimmune disorders of skin of unknown etiology and are characterized by the presence of immunoreactants in the skin and circulating autoantibodies to skin components. The distribution of IgG subclass antibodies to intercellular substance (ICS) of pemphigus and basement membrane zone substance (BMZ) of bullous pemphigoid was analyzed by using monoclonal antibodies to human IgG subclasses. IgG4 type anti-BMZ antibody was found in the majority of patients with bullous pemphigoid (88% in skin and 96% in serum). One third to one half of bullous pemphigoid patients had IgG1 and IgG2 anti-BMZ antibodies. The majority of bullous pemphigoid skin (92%) had complement in skin, however only one third of their sera had complement binding activity in vitro. IgG1 anti-ICS antibody was the predominant one in patients with pemphigus (86% in skin and 80% in circulation). IgG4 anti-ICS antibody was seen in two thirds of specimens from pemphigus patients. IgG3 subclass antibody was more frequently seen in pemphigus than in bullous pemphigoid patients. Two-thirds of pemphigus sera were capable of activating complement in vitro. The complement binding activity was directly associated with IgG1 and/or IgG3 subclass antibodies. The possible mechanisms for the restricted IgG4 subclass antibodies in bullous pemphigoid and pemphigus are discussed.     

Human IgG subclass measurements in the clinical laboratory

Complement activation, cell surface-receptor binding, blocking activity, and possibly placental transfer are among the biologically important functional differences that have been detected between the four human IgG subclasses by use of polyclonal antisera. In 1985, a IUIS/WHO panel of immunologists, using eight immunological methods, documented the specificity of select monoclonal antibodies for the IgG subclasses. Clinical assays have been developed involving these monoclonal antibodies that allow quantification of the concentration of IgG subclass protein and distribution of the IgG subclass antibodies in human immune responses. This review addresses issues of concern to investigators who are evaluating and (or) developing quantitative human IgG subclass assays in the clinical laboratory. Unique physical (structural) and biological (functional) properties of human IgG subclasses are summarized, with a focus on aspects pertinent to their clinical importance and in vitro quantification. The HP-series monoclonal antibodies with documented specificity are examined within the context of their application to several immunological methods. I describe unique technical aspects of total and antigen-specific IgG-subclass immunoassays involving these monoclonal antibodies. Finally, this report outlines clinical applications and indications for IgG-subclass measurements in the study of human health and disease.     

Diagnostic value of anti-arc 5 IgG antibody and analysis of the IgG subclasses in sera of patients with cystic hydatid disease

Serodiagnosis of cystic hydatid disease (CHD) due to the metacestode of Echinococcus granulosus depends on detecting antibodies specific to hydatid antigen, but cross-reactivity with other parasites is one of the major draw-backs. We used a commercially-available antigen that elicits the arc 5 in immunoelectrophoresis and analysed the immunoglobulin class and the IgG subclass response by an ELISA. We tested sera from patients with confirmed CHD, cystic mass/lesions (CML) of non-hydatid origin, cysticercosis and healthy controls. High levels of antibodies to the hydatid antigen in all three classes (IgG, IgM and IgA) were observed only in the CHD patients. Significantly, only IgG antibody levels were discriminative and of diagnostic value. Also discussed is the validity of reading the significant cut-off point in IgG-ELISA in relation to a clinically important group of patients such as those with a CML of non-hydatid origin rather than healthy controls. Analysis of the anti-arc 5 IgG subclass responses demonstrated high antibody responses in all subclasses among the hydatid patients, with IgG3 the most discriminatory. The significance of the elevation of all four subclasses and more specifically of IgG4 in CHD is discussed in relation to certain biological activities of these immunoglobulin molecules.     

IgG heavy-chain subclass restriction of thyrotropin-binding inhibitory immunoglobulins in Graves'' disease

The IgG subclass composition of antibodies is an important determinant of their function. Thyrotropin receptor antibodies cause the hyperthyroidism of Graves' disease but their subclass distribution has been incompletely investigated. We have therefore purified IgG subclasses from Graves' sera by passage over affinity columns designed to deplete all but a single subclass, and then assayed those pure subclass fractions for their ability to displace radiolabelled thyrotropin from its solubilized receptor as a measure of thyrotropin receptor antibody activity. Sufficient activity was recovered for analysis in nine of 10 Graves' patients, in five of whom activity was almost completely (97-100%) restricted to the IgG1 subclass; in the remaining four patients the response was predominantly IgG1 and IgG4 with marked under-representation of the IgG2 subclass. This contrasts with the unrestricted subclass response, in the same fractions, for autoantibodies against thyroglobulin and microsomes. These results suggest that there may be a primary defect at the B-cell level in Graves' disease.     

IgG subclass distribution and relative functional affinity of thyroid microsomal antibodies in postpartum thyroiditis

An association between the development of postpartum hypothyroidism and high levels of IgG1 subclass microsomal (M) antibodies has been reported. Using an assay designed to detect reasonable levels of all the four IgG subclasses, we found no differences in the proportion of each IgG subclass in M antibodies of patients with postpartum hyperthyroidism or hypothyroidism compared with control postpartum patients with M antibodies but no thyroid dysfunction. However the total amount of M antibody of each IgG subclass was elevated above the controls in the patients with thyroid dysfunction. The relative functional affinity of M antibodies did not differ between controls and patients with hypothyroidism but declined 5 and 10-12 months after delivery compared to values at 2 months. These results do not support the suggestion that the amount of IgG1 subclass M antibodies particularly determines the course of postpartum thyroiditis. Rather, the total M antibody level, in all four subclasses, is associated with clinical outcome. Resolution of the disease, despite persisting M antibodies, may occur in part because the relative functional affinity of these antibodies declines after delivery.     

Immunoglobulin G subclass responses to cytomegalovirus in seropositive patients after transfusion

The immunoglobulin G subclass responses to cytomegalovirus (CMV) after red cell (RBC) transfusion were studied in 26 seropositive surgery patients and 34 transfused seropositive oncology patients. Also included as controls were 18 surgical patients who received no RBCs during surgery. None of the 78 patients studied had IgG2 to CMV before or after transfusion. The absence of a total IgG response to CMV after transfusion could not be attributed to preexisting deficiencies in one or more subclasses, because all 78 patients had similar levels of IgG1, IgG3, and IgG4 to CMV before transfusion. Discriminant analysis was used for statistical evaluation of the combined CMV subclass responses in each patient and the individual subclass responses. Individual patients responded to CMV antigens with an increase in concentration in any of the three subclasses or any combination of the subclasses, excluding IgG2. IgG subclass analysis showed that 10 of 27 patients who did not respond with at least a fourfold total IgG titer rise had a significant increase in IgG subclass antibodies to CMV. Three of 33 patients with at least a fourfold total IgG titer rise lacked a subclass response. These results suggest that the measurement of IgG subclasses may be a sensitive indicator of immune response to CMV.     

Quantitation of IgG subclass antibodies to pneumococcal capsular polysaccharides by ELISA, using Pneumovax-specific antibodies as a reference

A quantitative enzyme-linked immunosorbent assay (ELISA) method has been developed to assay the levels of IgG subclasses to pneumococcal capsular polysaccharides (PCP) by using a reference standard. This standard solution containing specific antibodies to a polyvalent pneumococcal vaccine (Pneumovax) was purified from the serum of an immunized healthy adult by affinity chromatography. In order to determine the predominant response to Pneumovax in the four IgG subclasses, specific IgG subclasses in preimmune and postimmune sera from six healthy adults were assessed quantitatively by the ELISA. With regard to peak concentrations after immunization, there was a marked increase in the IgG2 subclass, compared with those of IgG1 and IgG3. Such a quantitative assay of Pneumovax-specific IgG subclass antibodies is useful for the direct evaluation of immune responses to immunization with a polyvalent pneumococcal vaccine, and at the same time, for estimating the IgG2 response to PCP antigens in individuals.     

Antibody isotype responses in Aspergillus-induced diseases

The Aspergillus fumigatus-specific immunoglobulin class and subclasses were evaluated in the sera of patients with allergic bronchopulmonary aspergillosis, aspergilloma, patients with asthma and immediate wheal-and-flare skin test reactivity to Aspergillus antigens, and normal controls. A sensitive sandwich enzyme immunoassay using a biotin-avidin amplification system was used to detect the specific antibodies. No difference was demonstrated in the specific antibody levels against A. fumigatus between the normal controls and A. fumigatus skin test-reactive asthmatic subjects except for immunoglobulin IgD and IgG4 isotypes. Allergic bronchopulmonary aspergillosis (ABPA) sera showed significant elevation of A. fumigatus-specific antibodies of all isotypes. On the other hand, aspergilloma sera, when compared with that of asthmatic individuals, showed significant increases of IgA, IgG1, IgG2, and IgG3 antibodies. The specific antibodies belonging to both IgG1 and IgG2 subclasses were elevated in ABPA, the former predominant in 40% of cases and the latter in 60%, while in aspergilloma IgG1 was predominant. Among the initially diagnosed ABPA patients, all specific Ig isotypes were considerably elevated when compared with sera from other patients being treated with prednisone or when compared with sera from patients who became asymptomatic after treatment.     

Thyroid-stimulating antibody activity between different immunoglobulin G subclasses

To investigate the distribution of thyroid-stimulating antibody (TSAb) activity between IgG subclasses, sera from 11 patients with Graves disease (including the National Institute of Biological Standards and Control (NIBSC) Research Standard, long acting thyroid stimulator-B) were fractionated by chromatography on affinity columns of monoclonal IgG subclass antibodies or protein A to deplete all but a single subclass. The resulting fractions were 98% or more pure for a single subclass. In all 11 patients, TSAb activity appeared to be confined to the IgG1 fraction as determined by cAMP production on addition of the fractions to the FRTL-5 rat thyroid cell line. In all of eight specimens from seven patients so tested, the whole serum activity was recovered in the IgG1 fraction, after adjusting for the recovery of the isotype from the column. TSAb activity in one serum comprised both lambda and kappa light chains but was IgG1 restricted. This IgG subclass restriction was not found when the same fractions were tested for thyroglobulin, microsomal/thyroid peroxidase, or tetanus toxoid antibody activity. Together with previous results showing marked restriction of both light chain usage and isoelectric point of TSAb, these results support the idea that Graves' disease may be the result of an oligo- or possibly monoclonal response at the B cell level.     

IgG heavy-chain subclass typing of myeloma paraproteins by isoelectric focusing immunoblot analysis

The objective of this study was to develop a clinical laboratory method for subclass typing of human immunoglobulin G (IgG) paraproteins. Serum proteins were isoelectrically focused (IEF) in a mini-gel and passively blotted by capillary diffusion onto untreated nitrocellulose. Unreacted sites on the nitrocellulose were blocked with bovine serum albumin and the bound IgG was detected with peroxidase-conjugated anti-human IgG1-4 monoclonal antibodies from WHO/IUIS clones. The IEF immunoblot specificity was demonstrated by analysis of documented IgG, IgA, and IgM myeloma proteins of known subclass and light-chain composition. IEF immunoblots of sera from 18 myeloma patients who had an above-normal total IgG concentration produced IEF immunoblot patterns composed of five to 10 discrete bands (pI range 6.0 to 8.4). In contrast, no detectable IgG bands were observed with sera containing IgA and IgM paraproteins. The observed subclass frequencies of IgG paraproteins were 56% IgG1 (10/18), 28% IgG2 (5/18), 11% IgG3 (2/18), and 5% IgG4 (1/18). IEF immunoblot analysis permits the monitoring of changes in the pI and subclass of an IgG paraprotein over the course of a myeloma patient's therapy program.     

Differences in the characteristics of human monoclonal and polyclonal anti-D as revealed by immunochemical investigations: human monoclonal antibodies share specificities with natural antibodies

To determine the basis of the tissue cross-reactions shown by some human monoclonal anti-Rh D antibodies, we have investigated the tissue reactivities of 48 further human monoclonal antibodies (mAb) against D and other Rh antigens, and compared them with those of normal and anti-D sera and immunoglobulin preparations, and affinity-purified polyclonal anti-D antibodies. Although we were unable to detect any tissue reactivities associated with the D-binding fraction of polyclonal antisera or prophylactic immunoglobulin, the non-erythroid cell types identified by the tissue-reactive human anti-Rh mAb of both IgM and IgG class were those recognized by antibodies present in both normal and anti-D sera. These results indicate: (a) that the tissue specificities of human anti-Rh mAb are similar to those of natural antibodies, and (b) that there are immunochemical differences between polyclonal and monoclonal anti-D antibodies, at least of IgG class, which may be relevant to the use of the latter in the prevention of haemolytic disease of the new-born by immune prophylaxis.     

Pemphigus immunoglobulin G subclass autoantibodies: studies of reactivity with cultured human keratinocytes

The subclass distribution of pemphigus vulgaris (PV) autoantibodies has been investigated further. Cultured human keratinocytes (HuKs) were incubated with immunoglobulin G (IgG) fractions prepared from the serum samples of five patients with PV and one patient with pemphigus foliaceus (PF). The binding of IgG subclasses to HuK was detected by the use of indirect immunofluorescence done with monoclonal antibodies that were specific for each of the four human IgG subclasses. IgG1 and IgG4 binding to keratinocytes was detected in all of the pemphigus IgG preparations. In each instance, the titer of bound IgG1 was equal to or greater than the IgG4 titer. IgG3 binding was detected in only one PV IgG, and IgG2 pemphigus antibody activity was not detected. Differences in the immunofluorescence patterns between the five PV and one PF IgG and between the five PV and a second PF serum were noted. PV antigens were detected as a speckled pattern on HuKs, with accentuation in the intercellular spaces. By comparison, the pattern of PF antigen expression varied significantly depending on whether anti-IgG1 or anti-IgG4 antisera were used. Anti-IgG1 bound in a coarse granular pattern without accentuation in the intercellular spaces, but anti-IgG4 bound in a pattern nearly identical to that observed with PV IgG and its subclasses.     

Evaluation of four commercially available ELISA assays for the serologic diagnosis of Lyme disease

We evaluated four commercially available ELISAs for detection of antibody to Borrelia burgdorferi with 21 sera from patients with clinically diagnosed Lyme disease and 89 patient control sera. Patient control sera included 28 sera from patients with rheumatoid arthritis (RA), 17 sera from patients with systemic lupus erythematosus (SLE), and 44 sera containing antibodies reported to cross-react in some Lyme disease tests. The ELISAs tested (Cambridge Bioscience, Diamedix, 3M, and Zeus) detect antibodies (IgM and/or IgG) that bind Borrelia burgdorferi antigen attached to microtiter wells. Antibody reactivity in the sera from patients with clinically diagnosed Lyme disease was characterized by using Zeus immunoglobulin class-specific assays (IgM and IgG). Sensitivities in early and late Lyme disease were as follows: Cambridge and Diamedix, 57% and 100%; 3M, 57% and 93%; and Zeus, 71% and 86%. Reactivities within a patient control population were: Cambridge and Diamedix, 3%; 3M, 7%; and Zeus, 10%.