Application of the enzyme-linked immunosorbent assay (ELISA) in the serodiagnosis of syphilis

CDC Laboratory Recommendations for Syphilis Testing, United States, 2024

This report provides new CDC recommendations for tests that can support a diagnosis of syphilis, including serologic testing and methods for the identification of the causative agent Treponema pallidum. These comprehensive recommendations are the first published by CDC on laboratory testing for syphilis, which has traditionally been based on serologic algorithms to detect a humoral immune response to T. pallidum. These tests can be divided into nontreponemal and treponemal tests depending on whether they detect antibodies that are broadly reactive to lipoidal antigens shared by both host and T. pallidum or antibodies specific to T. pallidum, respectively. Both types of tests must be used in conjunction to help distinguish between an untreated infection or a past infection that has been successfully treated. Newer serologic tests allow for laboratory automation but must be used in an algorithm, which also can involve older manual serologic tests. Direct detection of T. pallidum continues to evolve from microscopic examination of material from lesions for visualization of T. pallidum to molecular detection of the organism. Limited point-of-care tests for syphilis are available in the United States; increased availability of point-of-care tests that are sensitive and specific could facilitate expansion of screening programs and reduce the time from test result to treatment. These recommendations are intended for use by clinical laboratory directors, laboratory staff, clinicians, and disease control personnel who must choose among the multiple available testing methods, establish standard operating procedures for collecting and processing specimens, interpret test results for laboratory reporting, and counsel and treat patients. Future revisions to these recommendations will be based on new research or technologic advancements for syphilis clinical laboratory science.

The endemic treponematoses

The agents of human treponematoses include four closely related members of the genus Treponema: three subspecies of Treponema pallidum plus Treponema carateum. T. pallidum subsp. pallidum causes venereal syphilis, while T. pallidum subsp. pertenue, T. pallidum subsp. endemicum, and T. carateum are the agents of the endemic treponematoses yaws, bejel (or endemic syphilis), and pinta, respectively. All human treponematoses share remarkable similarities in pathogenesis and clinical manifestations, consistent with the high genetic and antigenic relatedness of their etiological agents. Distinctive features have been identified in terms of age of acquisition, most common mode of transmission, and capacity for invasion of the central nervous system and fetus, although the accuracy of these purported differences is debated among investigators and no biological basis for these differences has been identified to date. In 2012, the World Health Organization (WHO) officially set a goal for yaws eradication by 2020. This challenging but potentially feasible endeavor is favored by the adoption of oral azithromycin for mass treatment and the currently focused distribution of yaws and endemic treponematoses and has revived global interest in these fascinating diseases and their causative agents.

The laboratory diagnostics of syphilis: yesterday, today, tomorrow

The article covers issues related to the development of laboratory methods used for the diagnostic of syphilitic infection in the historical aspect as well as for the nearest and remote future. Priorities of the application of several diagnostic methods have been highlighted depending on the stage and form of syphilis, on the performed specific treatment and the contingent of examined patients. The authors give recommendations for its use reflected in modern Russian and foreign manuals and standards of syphilis diagnostics. Laboratory methods such as immunochemiluminescence assay, хМАР-technology and aspects of their clinical application are specially highlighted. The authors provide data on applied methods of molecular typing of Т. pallidum and detection of genetic determinants of the resistance of the syphilis pathogen to antimicrobial substances.

It is time to use treponema-specific antibody screening tests for diagnosis of syphilis

Assays that detect treponema-specific antibodies, which are either automated or can be done as point-of-care tests, have been developed, some of which are FDA approved. These assays have the advantage of being easily performed and demonstrate high sensitivity, both key features of an infectious disease screening test. As a result, many high-volume clinical laboratories have begun to offer a reverse syphilis testing algorithm where a treponema-specific test is used for screening, followed by a nontreponemal test (i.e., rapid plasma reagin [RPR]) to assess disease activity and treatment status. Concerns about physicians being able to understand and apply this new testing algorithm have been expressed (8). In this point-counterpoint, Michael Loeffelholz of the University of Texas Medical Branch at Galveston explains why his laboratory has adopted this reverse algorithmic approach. Matthew Binnicker of the Mayo Clinic, Rochester, MN, explains why the reverse algorithm may not be suitable for all clinical laboratories and every clinical situation.

Prospects of using proteome technologies in the diagnostics of sexually transmitted infections and skin diseases

The article presents data from the literature describing up-to-date syphilis diagnostics methods used in the Russian Federation. It also describes main proteome techniques and gives the results of applying proteome technologies in the diagnostics of diseases including infectious ones, and prospects and opportunities for using direct proteome profiling to develop a new method for syphilis diagnostics are analyzed.

Comparative evaluation of nine different enzyme-linked immunosorbent assays for determination of antibodies against Treponema pallidum in patients with primary syphilis

Nine different enzyme-linked immunosorbent assays (ELISAs) with a sonicate or recombinant proteins of Treponema pallidum as antigen have been evaluated comparatively by testing 52 highly selected sera from patients with primary syphilis, all negative in the microhemagglutination test for T. pallidum (MHA-TP). Eight tests exhibited greater sensitivity (48.5 to 76.9%) than the commonly used Venereal Disease Research Laboratory test (44.2%). Higher sensitivity could be related to (i) the volume and dilution of the serum, (ii) the design of the assay (capture and competitive tests showed higher sensitivity than sandwich-based assays), and (iii) the ability to detected specific immunoglobulin M antibodies. The specificity of the ICE Syphilis and the Enzygnost Syphilis tests was 99.5 and 99.8%, respectively, as determined by routine testing of 2, 053 unselected sera in comparison with the MHA-TP test. ELISAs tested offered high sensitivity in patients with primary syphilis; however, recommendations to use these tests as screening assays do need further data on specificity and reactivity in late stages of the disease.

Evaluation of a Treponema pallidum enzyme immunoassay as a screening test for syphilis

The CAPTIA Syphilis-G enzyme immunoassay for the detection of antibodies to Treponema pallidum was evaluated as a screening test for syphilis in comparison with the standard rapid plasma reagin (RPR) test. One thousand samples were tested, and the standard fluorescent treponemal antibody absorption test and the standard microhemmaglutination test were used to confirm the presence of treponemal antibodies. Diagnosis of syphilis was based on traditional standard serology results. Clinical data used in the diagnosis of patients whose samples yielded conflicting results were provided by physicians. Initially, 7 patients whose samples were reactive in the RPR test and 14 patients whose samples yielded positive or equivocal results in the CAPTIA Syphilis-G test were diagnosed as not being infected. After discrepancies due to technical problems were reconciled, samples from six patients remained reactive in the RPR test and that from one patient remained positive in the CAPTIA Syphilis-G test. In addition, seven patients whose samples were nonreactive in the RPR test and two patients whose samples were negative in the CAPTIA Syphilis-G test were diagnosed as having untreated syphilis. After discrepancies were reconciled, samples from five patients remained nonreactive in the RPR test and none remained negative in the CAPTIA Syphilis-G test. Final results indicate that the specificities are 99.4 and 99.9%, respectively. In addition to the improved sensitivity and specificity of the CAPTIA Syphilis-G screen, other potential benefits of this assay lead us to believe that this method could serve as a better screening tool than the RPR test.

Enzyme immunoassay for anti-treponemal IgG: screening or confirmatory test?

AIMS

To review the performance of the Venereal Diseases Research Laboratory (VDRL) test and the Treponema pallidum haemagglutination assay (TPHA) as a combined screen for syphilis to provide a baseline for assessing screening by anti-treponemal IGG EIA.

METHODS

Between 1980 and 1987 all serum samples were screened by both VDRL and TPHA tests. The FTA-ABS test was also used in suspected early primary syphilis, or when one of the other tests was positive. A positive result in a screening test was confirmed by quantitative testing. From 1988 all specimens were screened with an enzyme immunoassay (Captia Syph G) as a single screening test.

RESULTS

Of the 44 primary, 47 secondary, and 38 early latent cases of syphilis, the VDRL and TPHA detected 32 (73%) and 31 (71%) of the primary cases; the combination detected 37 (84%). All 85 cases of cases of secondary and early latent infection were reactive in the TPHA test, whereas the VDRL was reactive in only 68 (80%). EIA had a reported sensitivity of 82% for primary infection.

CONCLUSIONS

EIA can be used as a single screening test for detecting early syphilis because its results are comparable with those of the combined VDRL and TPHA tests. The conventional VDRL test should not be used as a single screening test.

Evaluation of the Captia enzyme immunoassays for detection of immunoglobulins G and M to Treponema pallidum in syphilis

Two new enzyme-linked immunosorbent assays (ELISA), one for the measurement of immunoglobulin G (IgG) (Captia Syphilis-G) and one for the measurement of IgM (Captia Syphilis-M), were evaluated for detecting antibodies to Treponema pallidum. Serum samples from 169 patients, 96 with various stages of untreated syphilis, 63 with treated syphilis, and 10 who were noninfected, were investigated. All sera were also examined by traditional treponemal and cardiolipin tests and by the fluorescent treponemal antibody absorption (FTA-ABS) test for 19S(IgM). The overall sensitivity of Captia Syphilis-G was 98.3%. The IgG ELISA was very sensitive (100%) in all stages of untreated syphilis, except in primary syphilis (82%). In all diagnostic groups of syphilis, the reactivity of Captia Syphilis-M was similar to that of the 19S(IgM) FTA-ABS test, except in reinfections, in which the IgM capture ELISA was less sensitive. False-positive IgM capture ELISA results were not found in the 10 neonates born to mothers adequately treated for syphilis. However, of six serum samples containing rheumatoid factor, two were reactive in the Captia Syphilis-M test but not in the 19S(IgM) FTA-ABS test. This indicated that the specificity of the IgM capture ELISA was not absolute. All serum samples from treated patients were reactive in the IgG ELISA, but only 15 samples were reactive in the IgM capture ELISA, which appeared to be as effective as the 19S(IgM) FTA-ABS test in monitoring the effect of treatment. Simultaneous measurement of IgG and IgM antibodies for T. pallidum by the Captia immunoassays appears to be an efficient and simple method for confirming the diagnosis of syphilis as well as for indicating whether active disease is present.

Evaluation of the equivocal test results of Treponema pallidum haemagglutination assay

Two hundred and eighty Rapid Plasma Reagin (RPR) positive sera with an emphasis on cases with negative and borderline positive Treponema pallidum haemagglutination assay (TPHA) results were selected. Modified TPHA (M-TPHA) and fluorescent treponemal antibody absorption (FTA-abs) tests were used for comparison. One hundred and twenty five samples were TPHA negative, of which 78 and 69 cases were also negative by M-TPHA and FTA-abs, respectively. Eighty one sera negative by TPHA at a titre of 1/80 and positive at 1/40, considered to be negative according to the manufacturer's instructions, were also negative by M-TPHA (n = 11) and by FTA-abs (n = 1). Fifty borderline positive TPHA specimens gave one negative result by both M-TPHA and FTA-abs. The remaining 24 sera were positive by all three tests. Because of the high percentage of TPHA negative results among the positive RPR sera which became reactive when rechecked by the FTA-abs, it is concluded that as a confirmatory test the TPHA should be used not instead of but in addition to the FTA-abs.

Screening for treponemal infection by a new enzyme immunoassay

A new enzyme immunoassay (EIA, Captia Syphilis-G) for detecting IgG antibodies against Treponema pallidum was evaluated as a screening test for syphilis. When serum samples were tested at a dilution of 1 in 20 (EIA20), the overall agreement between the IgG EIA and serological status based on the T pallidum haemagglutination assay (TPHA) and the fluorescent treponemal antibody absorption (FTA-ABS) test was 99.2% (1310/1321). The sensitivity of the EIA20 was 98.4% (60/61) and the specificity 99.3% (1251/1260). Discrimination between patients with and without treponemal infection was good: the mean EIA20 absorbance ratios (patient/mean low titre positive control results) were 0.49 for antibody negative patients, 3.30 for patients with positive Venereal Diseases Research Laboratory (VDRL) test and TPHA results, and 1.77 for patients with negative VDRL but positive TPHA results. The cut off point for excluding treponemal infection was taken as 0.9. Specimens with ratios of more than 0.9 should be confirmed by the FTA-ABS test and evaluated for specific IgM antibodies to treponemes. When serum samples were tested at a 1 in 50 dilution (EIA50) the sensitivity was lower (80.3%) but the specificity was absolute. The reduction in sensitivity correlated with low absorbance ratios in the patients who were VDRL negative and TPHA positive. The screening performance of the IgG EIA20 is thus comparable with that provided by a combination of the VDRL test and TPHA. The potential for automation makes the EIA an attractive alternative, particularly in larger centres. Alternatively, the test can be performed at a 1 in 50 dilution (EIA50), at which level it is ideally suited for confirming the treponemal status of antibodies in serum samples preselected by positive cardiolipin antigen screening test results.

Enzyme linked immunosorbent assays with Treponema pallidum or axial filament of T phagedenis biotype Reiter as antigen: evaluation as screening tests for syphilis

Enzyme linked immunosorbent assays with an ultrasonicate of Treponema pallidum (TP-ELISA) or axial filament of Treponema phagedenis biotype Reiter (AF-ELISA) were developed to detect treponemal antibody. TP-ELISA and AF-ELISA were compared with the T pallidum haemagglutination assay (TPHA), the fluorescent treponemal antibody-absorbed (FTA-ABS) test, and the Venereal Disease Research Laboratory (VDRL) test for sensitivity and specificity of serodiagnosis of syphilis. A total of 1423 serum samples, 253 from patients with various stages of syphilis, 500 from patients attending a sexually transmitted disease (STD) clinic, and 670 from people without syphilis, were investigated. At all stages of syphilis the sensitivity of the TP-ELISA, the AF-ELISA, the TPHA, and the FTA-ABS test did not differ significantly, except that the AF-ELISA was less sensitive than the TPHA (p less than 0.05) for treated syphilis. In primary syphilis, neurosyphilis, and treated syphilis the TP-ELISA and AF-ELISA were significantly more sensitive than the VDRL test (p less than 0.05). The specificity of all tests was comparable (p greater than 0.05). The TP-ELISA and AF-ELISA appear to be good alternatives to the TPHA as screening tests for syphilis. Because of the easy availability of a well defined antigen the AF-ELISA seems to be better suited for large scale testing.

Treponemal antibody-absorbent enzyme immunoassay for syphilis

An enzyme immunoassay for the diagnosis of syphilis (ELISA-SY) was developed with solid-phase extracts of Treponema pallidum, specimen diluent containing Reiter treponeme absorbent, and three 30-min incubations. The ELISA-SY results were determined in comparison with a standardized positive control and reported as a percentage of strong positive control. In tests with 1,005 serum samples from a venereal disease clinic and other sources, 98.2% agreement was found with fluorescent treponemal antibody-absorption (FTA-ABS) results, and 98.3% agreement was found with T. pallidum passive hemagglutination (PHA) findings. Only 1 of 29 sera originally considered to be biologically false-positive by ELISA-SY; the latter specimen was also positive by PHA and FTA-ABS tests performed in our laboratories. Serum samples from clinically diagnosed syphilitics (16 primary-stage isolates, 7 secondary-stage isolates, and 3-latent-stage isolates) were all positive by ELISA-SY, FTA-ABS, and PHA. Serum samples from 51 newborns suspected of having syphilis on the basis of positive cardiolipin flocculation tests showed 98% agreement of ELISA-SY results with FTA-ABS and PHA findings. Sera from all 61 patients with a variety of autoimmune and other diseases known to be associated with biologically false-positive reactions for syphilis were negative by this ELISA-SY. The specificity of the ELISA procedure for T. pallidum antibody was also confirmed immunologically by blocking experiments.

Percoll-purified Treponema pallidum, an improved fluorescent treponemal antibody-absorbed antigen

Percoll-purified Treponema pallidum was evaluated as a fluorescent treponemal antibody-absorbed antigen. Borderline and false-positive reactions were essentially eliminated, resulting in sensitivity and specificity of 100 and 95.5%, respectively. The lack of background debris improved the ease and speed of reading the test.

Enzyme-linked immunoassays for the detection of microbial antigens and their antibodies

Antibodies could be labeled with enzymes for use in histochemical staining procedures by enzyme-immunoassay (EIA). The use of EIA is an extension of previously used serological tests, using enzyme-labeled antibody or antigen to determine antibody content. Direct detection of antigen by EIA represents a more dramatic departure from previous methods based on culture. Also, the method has enabled detection of infectious agents that are difficult to cultivate, such as hepatitis A virus and rotavirus, or agents that cannot be cultivated, such as hepatitis B. The use of EIA tests for detection of microbial antigens provides an alternative to culture as a means for direct identification of a specific microbial agent. It also provides a means to detect microbial agents which have not been successfully propagated. The detection of circulating antigen or detection of antigen in other body fluids by EIA is more difficult than detection of antibody because of the sensitivity required, and because of interfering substances in specimens such as feces and respiratory secretions. For this reason, very few antigen detection assays have the sensitivity and specificity required to be used as a primary diagnostic test. The number of tests that have been developed, however, is impressive and because of the possibilities for rapid, specific diagnosis, the interest in antigen detection by EIA remains high.

Evaluation of an enzyme-linked immunosorbent assay for treponemal antibody

A new enzyme-linked immunosorbent assay with Treponema pallidum antigen bound to ferrous metal beads (Syphilis Bio-EnzaBead; Litton Bionetics Laboratory Products) was compared with the standard fluorescent treponemal antibody-absorption test for syphilis. Bio-EnzaBead and fluorescent treponemal antibody-absorption tests were done on 218 specimens from documented cases of syphilis, on 315 sera from individuals with diseases other than syphilis, and on sera submitted to a public health laboratory for premarital (304 specimens) or diagnostic (501 specimens) tests for syphilis. Agreement between the Bio-EnzaBead and reference tests ranged from 93.0% for sera for the diagnostic test to 99.5% for sera from patients with syphilis. The overall agreement among the 1,338 sera tested was 96.3%. The reproducibility of the Bio-EnzaBead test with 60 coded sera of graded reactivity was 97%. The test is easy to perform, the indicator results are clear and unequivocal, and the findings are comparable to those of the fluorescent treponemal antibody-absorption test.

Four-step enzyme-linked immunosorbent assay for detection of Treponema pallidum antibody

Further studies of a four-step enzyme-linked immunosorbent assay procedure to detect Treponema pallidum antibody are described. High-titered antibody, produced in rabbits by intravenous injection of T. pallidum, was used to coat polyvinyl chloride microtiter plates. To these plates a known concentration of T. pallidum was added, followed in successive steps by serial dilutions of human sera and appropriately diluted peroxidase-labeled anti-human immunoglobulin G antibody. O-Phenylenediamine was the substrate. A total of 340 sera were obtained from the DeKalb County Sexually Transmitted Diseases Clinic, Atlanta, Ga., and examined within 3 days of receipt. Ninety-six percent test agreement between the enzyme-linked immunosorbent assay and the fluorescent treponemal antibody absorption-double staining test was obtained. A total of 372 additional sera stored at -20 degrees C were examined. The overall sensitivity of the enzyme-linked immunosorbent assay with sera from patients with various stages of syphilis was 96%. With sera from uninfected individuals, the specificity of the enzyme-linked immunosorbent assay was 95%. No antigen instability was noted with the two antigen preparations used during this evaluation.

Molecular cloning and expression of Treponema pallidum DNA in Escherichia coli K-12

A gene bank of Treponema pallidum DNA in Escherichia coli K-12 was constructed by cloning SauI-cleaved T. pallidum DNA into the cosmid pHC79. Sixteen of 800 clones investigated produced one or more antigens that reacted with antibodies from syphilitic patients. According to the separation pattern of the antigens produced on sodium dodecyl sulfate-polyacrylamide gels, six different phenotypes were distinguished among these 16 clones. These antigens reacted also with anti-T. pallidum rabbit serum. No antibodies against the cloned antigens were found in normal rabbit serum and in nonsyphilitic human serum. The antigens produced by the E. coli K-12 recombinant DNA clones comigrated in sodium dodecyl sulfate-polyacrylamide gels with antigens extracted from T. pallidum bacteria, suggesting that the treponemal DNA is well expressed in E. coli K-12. Several of the cosmid recombinant plasmids have been subcloned, resulting in smaller T. pallidum recombinant plasmids which are more stably maintained in the cell and produce more treponemal antigen. Monoclonal antibodies were raised against T. pallidum, and one hybridoma produced antibodies that reacted not only with an antigen from T. pallidum but also with the antigen produced by one of the E. coli clones.

Microenzyme-linked immunosorbent assay for the detection of specific IgM antibodies in human syphilis

An enzyme-linked immunosorbent assay (ELISA) using a highly purified soluble antigen prepared from pathogenic Treponema pallidum (Nichols) was carried out to detect specific IgM antibodies in syphilis. Serum specimens from 365 patients with untreated or treated syphilis were tested by the ELISA and by the 19S(IgM) fluorescent treponemal antibody-absorbed test. In the ELISA sera were preabsorbed with aggregated human IgG to eliminate any rheumatoid factor present. Sera from 331 healthy blood donors served as controls. The results of both tests correlated well. The specificity and sensitivity of the treponemal ELISA were both greater than 97%. The assay was easy to perform and may be automated.

Sodium desoxycholate-extracted treponemal antigen in an enzyme-linked immunosorbent assay for syphilis

The extraction of Treponema pallidum antigen with sodium desoxycholate, based on a previously described procedure (J. Portnoy and H.J. Magnuson, J. Immuno. 75:348-355, 1955), was used in an enzyme-linked immunosorbent assay (ELISA) test for syphilis. The antigen was prepared from T. pallidum street strain no. 14, and its overall sensitivity and specificity was compared with those of sonicated antigen preparations made with phosphate-buffered saline. The optimum serum dilution for testing and the significant absorbance reading at 490 nm were selected by examination of quantitative dilutions of 91 sera from presumably normal individuals and 92 sera from syphilitics. The time and temperature of serum and conjugate incubations were also examined. With an absorbance reading of greater than or equal to 0.2 at the 1:80 serum dilution, 88 (95.8%) of 92 sera from syphilitics were reactive in the ELISA test with desoxycholate-extracted antigen, and 82 (89.1%) were reactive with the sonicated antigen. Only one nonsyphilitic serum was reactive with each antigen. Greater sensitivity without loss in specificity was obtained with longer serum and conjugate incubations. We concluded that an ELISA test with sodium desoxycholate-extracted antigen is more sensitive than and equally specific to an ELISA with sonicated treponemal antigen.

Evaluation of the microenzyme-linked immunosorbent assay with Treponema pallidum antigen

Whole-cell sonicates of Treponema pallidum, Nichols strain, were evaluated in an enzyme-linked immunosorbent assay (Elisa) for syphilis, and results were read in a Dynatek Microelisa Reader. The antigen was evaluated with sera from patients with syphilis, persons presumed normal, and biological false-positives. Two hundred and ninety-seven sera were tested by the ELISA with T. pallidum antigens, the Venereal Disease Research Laboratory (VDRL) slide test, the fluorescent treponemal antibody absorption (FTA-Abs) test, and the microhemagglutination assay for T. pallidum antibodies (MHA-TP). The results of all of the tests were compared. The ELISA, with 89.3% sensitivity, was less sensitive than the VDRL (93.3%) and FTA-Abs (100.0%) tests but more sensitive than the MHA-TP (76.0%). THe ELISA was considerably more sensitive in primary syphilis than the MHA-TP. Specificity was as follows: ELISA, 98.5%; FTA-Abs test, 97.8%; MHA-TP, 98.2%; and VDRL test, 92.7%. The ELISA has good potential as a confirmatory test in the serodiagnosis of syphilis.

Solid-phase fluoroimmunoassay for treponemal antibody

An objective, solid-phase fluoroimmunoassay for treponemal antibody was developed with a lysate of virulent Treponema pallidum (Nichols strain) adsorbed on cellulose acetate disks. A probe containing both the antigen and control disks is inserted successively into a serum specimen dilution, a buffer rinse, fluoroscein isothiocyanate-conjugated goat anti-human immunoglobulin G, and a second buffer rinse. Fluorescence signal units are measured with a fluorometer. To establish test calibration curves, the corrected fluorescence values (antigen disk minus control) of reference sera are plotted against indirect fluorescent treponemal antibody test titers. The corrected fluorescence values obtained for 62 sera reactive in the fluorescent treponemal antibody absorption test ranged from 64 to 178; values for 66 nonreactive sera ranged from 20 to 46. Thus, the solid-phase fluoroimmunoassay for treponemal antibody clearly separated specimens from patients with documented primary, secondary, or latent disease from fluorescent treponemal antibody absorption-nonreactive sera. The test is technically simple and produces an objective quantitative result.

Uneven distribution of antitreponema antibody acitivity in differing immunoglobulin G fractions from patients with early syphilis

Three fractions, containing immunoglobulin G's (IgG's) of differing relative electrophoretic mobility, were isolated from sera of 33 male patients with untreated early syphilis. Serological testing, employing four different serodiagnostic procedures for these fractions at equal amounts of IgG, revealed a very constant reaction pattern for all patients. In the earliest stages of the disease, the most basic fraction was the first to show antibody activity. In progressive stages, antibody activity subsequently was also found in the two less basic fractions. However, in all stages of disease studied, the basic part of the IgG made the largest contribution of the total antibody activity within the IgG class, indicating an uneven distribution of antitreponema antibody activity over heterogeneous IgG. Several possible explanations of the observations are discussed.

Antigenic diversity of the serotype antigen complex of Neisseria gonorrhoeae: analysis by an indirect enzyme-linked immunoassay

An indirect enzyme-linked immunoassay (ELISA) has been developed to analyze the antigenic profile of the outer membrane serotype complex of Neisseria gonorrhoeae. Antisera raised in rabbits to serotype-specific vesicles (SSV) reacted primarily with homologous SSV; however, there was significant cross-reactivity (less than 50%) with heterologous SSV. N. meningitidis SSV cross-reacted with all antigonococcal SSV but at a lower degree (less than 20%). Preimmune sera did not cross-react significantly with all antigonoccoccal SSV. The sensitivity of the ELISA was enhanced when the integral SSV proteins 1a and 2 were used as adsorbed antigen. Heterologous anti-SSV cross-reacted slightly, having ELISA values less than 15% of the homologous reaction. Antisera prepared by immunoabsorbent affinity columns were highly specific. Homologous affinity anti-SSV reacted only with proteins 1a and 2. The reaction of immune sera was inhibited by homologous proteins 1a and 2; lipopolysaccharide and proteins 1a and 2 isolated from heterologous serotypes did not inhibit the reaction. The reaction of affinity-purified antisera could be inhibited only by homologous protein 1a. By the use of affinity-purified antisera, a specific and highly sensitive ELISA was developed to analyze the antigenic profile of strains of N. gonorrhoeae.

Measurement of immunoglobulin M (IgM), IgG, and IgA antibodies against Yersinia enterocolitica by enzyme-linked immunosorbent assay: persistence of serum antibodies during disease

An enzyme-linked immunosorbent assay for the detection and quantitation of human immunoglobulin M (IgM), IgG, and IgA antibodies against Yersinia enterocolitica is described. Formalinized or heat-treated bacteria were adsorbed onto specially designed microcuvettes, and antibodies were allowed to attach to the antigen-coated cuvettes. Rabbit anti-human mu, anti-human gamma, and anti-human alpha antisera were allowed to react with human antibodies, and these class-specific anti-immunoglobulins were detected by alkaline phosphatase-labeled swine anti-rabbit IgG. A total of 423 sera were tested. The results obtained with the enzyme-linked immunosorbent assay were compared with the results of the conventional tube agglutination test. Persistence of different antibodies was studied in six patients. Antibodies of the IgM class persisted only for 1 to 3 months after onset of the disease; thus the occurence of IgM-class Yersinia antibodies in a single sample indicates a recently acquired infection. The persistence of the IgG- and IgA-class antibodies was variable and not parallel with each other. Remarkably, all three patients in which the disease was complicated with arthritis had IgA-class Yersinia antibodies at the end of the follow-up period of 9 to 14 months, and in those without arthritis the IgA-class antibodies disappeared within 3 months after onset of the disease.

Enzyme immunoassays with special reference to ELISA techniques

In this review outlines are given on various types of enzyme immunoassay. The applications to such enzyme immunoassays, especially ELISA, are dealth with in detail. It is concluded that these techniques have high sensitivity and will be suitable in due course as routine laboratory tests.

Enzyme immunoassays in diagnostic medicine. Theory and practice

Serological methods are playing an increasingly important role in the diagnosis and epidemiological assessment of diseases. Simple, inexpensive methods for large-scale application are urgently needed. The enzyme immunoassay methods developed recently and reviewed here hold great promise for application in a wide variety of conditions. Under laboratory conditions they can be as sensitive as radio-immunoassay, but they can also be adapted as simple field screening procedures. These methods are based on the use of antibodies or antigens that are linked to an insoluble carrier surface. This is then used to "capture" the relevant antigen or antibody in the test solution and the complex is detected by means of an enzyme-labelled antibody or antigen. The degradation of the enzyme substrate, measured photometrically, is proportional to the concentration of the unknown "antibody" or "antigen" in the test solution. The application of these techniques to endocrinology, immunopathology, haematology, microbiology, and parasitology is reviewed.