Serological analysis of human tuberculosis by an ELISA with mycobacterial antigen 60

Liquid-Crystal-Based Immunosensor for Diagnosis of Tuberculosis in Clinical Specimens

Tuberculosis (TB) is a serious global health problem, although it is easily preventable and curable. The prevalence of TB is caused by a lack of simple, rapid, cheap, and effective TB diagnostic tests. In this study, we have established a novel liquid crystal (LC)-based immunosensor to diagnose TB in clinical specimens. The clinical serum samples were incubated on a TB antigen-immobilized substrate, and their optical LC responses were observed using a polarized light microscope. Specific binding of anti-TB antibodies to the TB antigen-immobilized surface only occurred in clinical specimens from TB patients, inducing the disruption of the orientation of LCs. This was followed by the distinctive change in the optical appearance of LCs from uniform to random. However, when clinical serum samples from healthy people or latent TB patients were incubated, the orientation of LCs remained uniform. Through the change of optical LC images, in 76% of TB patients, this essay correctly identified the patients as having antibodies to TB in their serums. 91% of healthy people free of TB were correctly identified as not having antibodies to TB. Thus, this LC-based immunosensor is a promising platform, particularly in clinical TB diagnostics, which does not require complicated preparation of clinical specimens or complex instrumentation.

Improved sensitivity for detection of tuberculosis cases by a modified Anda-TB ELISA test

Tuberculosis is still a major health problem in most developing countries and its incidence is rising in many industrial countries. The diagnosis of tuberculosis depends primarily on identification of mycobacteria and on clinicoradiological evidence of the disease. Compared to other diagnostic methods, serological tests are faster and do not necessarily require samples that contain the tubercle bacilli. We have evaluated a modified version of a commercially available enzyme immunoassay test to detect the presence of circulating anti-mycobacterial IgG and IgM antibodies in tuberculosis patients. The sensitivity and the specificity of the test reaches 87% and 95% respectively. In conclusion, the modified Anda-TB enzyme immunoassay test offers a good and reliable test for diagnosis of tuberculosis in suspected cases of active pulmonary tuberculosis.

Serological diagnosis of childhood tuberculosis by estimation of mycobacterial antigen 60-specific immunoglobulins in the serum

SETTING

An ELISA assay based on mycobacterial antigen 60 (A60) for the estimation of specific immunoglobulins in the serum has been used successfully for the rapid diagnosis of tuberculosis in studies done predominantly in Western countries. In a recent Indian study, encouraging results were reported in adult tuberculosis.

OBJECTIVE

To evaluate the utility of this ELISA test for rapid diagnosis of different clinical forms of tuberculosis in Indian children.

DESIGN

ELISA test based on mycobacterial A60 was used to estimate specific IgM, IgA and IgG antibodies in the sera obtained from 452 cases of tuberculosis and 161 controls in the paediatric population of Delhi, India.

RESULTS

Of the 161 controls, only 7.4% were positive for IgM, 4.3% for IgG, 3.7% for IgA and 8% when a combination of IgM and IgA was considered. Of 58 cases of definite pulmonary tuberculosis, 55.2% were positive for IgM, 32.7% for IgG, 36.2% for IgA and a high positivity of 72.4% was seen when IgA and IgM estimations were combined. The corresponding figures in 150 cases of definite extrapulmonary tuberculosis were 57.3%, 36.6%, 38% and 76.6%. A relatively weak serology was observed in 244 cases of probable tuberculosis. A very high positivity (95%) was seen in acid-fast bacilli-positive cases of tuberculosis.

CONCLUSIONS

Our findings point to a very good specificity (92%) and a reasonably good sensitivity (75.5%) of the test when combined IgM and IgA antibody titres are considered in the diagnosis of childhood tuberculosis.

Serodiagnosis of tuberculosis and leprosy by enzyme immunoassay

OBJECTIVE: To evaluate the use of serodiagnosis for tuberculosis and leprosy using mycobacterial antigen 38 kDa, with kits from Omega laboratories, to detect IgG by enzyme immunoassay (EIA). METHODS: The study population consisted of 58 patients with evidence of tuberculous infection (culture of Mycobacterium tuberculosis complex or microscopic evidence), of whom 23 had pulmonary and 35 had extrapulmonary disease. There were six subjects who had recently been treated for tuberculosis, 11 patients on treatment for leprosy and 137 patients suspected of having tuberculosis on clinical or radiologic grounds (without laboratory evidence). A control group comprised 35 healthy individuals or patients suffering from diseases other than tuberculosis. RESULTS: The tests showed that there was a significant difference in antibody levels between the patients with active pulmonary disease, extrapulmonary tuberculosis and leprosy in comparison with the control group (p<0.001). The sensitivities of the two tests together for proven pulmonary tuberculosis were 100% and 95.7% at 1.0--1.5 and >1.6 EIA cut-off points respectively, while the specificities were 88.5% and 100% at the same cut-off points. The sensitivities for extrapulmonary tuberculosis were 71.4% and only 51.4% at 1.0--1.5 and >1.6 EIA cut-off points. The test was positive in 30 (21.9%) of the 137 suspected patients, while 43 (31.4%) had an equivocal result and the remaining 64 (47.7%) suspects were definitely negative. There was again a significant difference in positivity rates between suspects and the control group. CONCLUSIONS: Omega IgG test is useful in the serodiagnosis of active pulmonary tuberculosis and leprosy, but less sensitive in extrapulmonary disease, particularly in children. Equivocal results may only add to the evidence of tuberculosis in early or minimal disease.

Serodiagnosis of tuberculosis: detection of mycobacterial antibodies and antigens

SETTING

The diagnosis of tuberculosis is based primarily on identification of mycobacteria and on clinical evidence. Recently, serological studies have been widely used experimentally as a diagnostic approach.

OBJECTIVE

The aim of our study was to optimize serodiagnosis of tuberculosis by detecting mycobacterial antigens and antibodies in sera from patients with lung tuberculosis, non-related diseases and healthy controls.

DESIGN

Mycobacterium tuberculosis H37Rv was disintegrated by pressure. Cell walls were extracted with 3 M KCL and were subjected to gel filtration in Toyopearl gel. Immune sera were prepared by immunization of rabbits with cell wall material. Anti H37Rv antibodies were purified by affinity chromatography. The reagents obtained were used to detect serum antibodies and antigens (following immune complex dissociation) using ELISA.

RESULTS

Using fraction 6 of cell wall extract, antibodies were detected in 72.2% of TB patients; there were no positive reactions in control subjects. By use of affinity-purified antibodies, antigens were detected in 77.1% of TB patients, 10% of patients with unrelated diseases and 6.7% of healthy controls.

CONCLUSION

Effective serodiagnosis of tuberculosis can be achieved only by combining detection of both circulating antibodies and antigens using highly specific purified reagents and immune complex-dissociated sera.

Tuberculosis antigen A60 serodiagnosis in tuberculous infection: application in extrapulmonary and smear-negative pulmonary tuberculosis

An ELISA diagnostic test for tuberculosis antigen A60 (TBA60) IgG/IgM was used in a tertiary referral hospital in Taiwan. From June 1992 to December 1993, serum samples obtained from 907 patients were analyzed for TBA60 IgG and IgM titres. The final diagnosis of these patients was confirmed by microbiological study and clinical follow up for 18-24 months. Among 147 patients with active pulmonary tuberculosis, IgG was positive in 112 (76.2%), IgM was positive in 14 (9.52%). Among 90 patients with active extrapulmonary tuberculosis, IgG was positive in 53 (58.9%), IgM was positive in 9 (10%). Among 153 patients with inactive tuberculosis, IgG was positive in 28 (18.3%), IgM was positive in 1 (1.6%). Among 517 patients with nontuberculous disease, IgG was positive in 50 (9.7%), IgM was positive in 3 (0.6%). In this study population with 26% (237/907) active tuberculous infection rate, the TBA60 ELISA IgG had a diagnostic sensitivity of 69.6% and a specificity of 92.1%. These results indicate a positive predictive value of 67.9% and a negative predictive value of 89.2%. The sensitivity of IgM was 10.5% and specificity, 99.4%. The serum IgG tire had good correlation with the extent of pulmonary TB had a higher percentage of IgG seropositivity (83.9%) than those with smear-negative pulmonary TB (70.6%) and extrapulmonary TB (58.9%). In 50 cases with active tuberculosis, follow-up examinations were carried out one month after treatment. In 18 cases with initially negative IgG and IgM titres, 13 showed elevation of serum IgG titres into positive level, one had positive seroconversion of IgM which was the only serological marker indicating active infection. Therefore, 77.8% (14/18) gained diagnostic benefit from follow-up serological examination. It was concluded that TBA60 IgG and IgM ELISA is a useful test when diagnosing tuberculosis. This test also assists in the clinical judgement of tuberculosis when used as an adjunct to symptoms and sputum smear, and for monitoring therapeutic response at the commencement of treatment.

Comparison of A60 and three glycolipid antigens in an ELISA test for tuberculosis

OBJECTIVES: To compare the diagnostic usefulness in tuberculosis of the serodiagnostic enzyme-linked immunosorbent assay (ELISA) kit A60 (Anda Biologicals, Strasbourg, France) and of our domestic ELISA based on three purified cell wall glycolipid antigens. METHODS: The presence and concentrations of IgG and IgM anti-A60 antibodies and anti-LOS, anti-DAT and anti-PGLTb1 antibodies against the glycolipid antigens were determined by ELISA in 50 HIV-seronegative and 46 HIV-seropositive patients, with documented active tuberculosis. The specificity of these ELISAs was determined with use of sera from 50 healthy blood donors, 29 patients with non-mycobacterial pulmonary diseases and 24 HIV-positive patients with disseminated Mycobacterium avium infection. RESULTS: With a calculated cut-off for each antigen and immunoglobulin that gave a specificity higher than or equal to 98%, the cumulative ELISA results showed that only 36.5% of the patients with tuberculosis had a positive response in the A60 test, as compared with 84.4% who showed a response to the three glycolipid antigens (p<0.001). This striking difference persisted when the cumulative sensitivities were calculated according to the HIV status of the patients and the localization of tuberculosis. The anti-A60 antibody (IgG and IgM) levels and the degree of sensitivity of the ELISA for detection of A60 antigen were always lower in HIV-positive patients with pulmonary and extrapulmonary tuberculosis than in HIV-negative patients with tuberculosis. The sensitivity of A60 ELISA was further decreased in HIV-positive patients with low CD4+ lymphocytes counts, in contrast to the results with the three glycolipid antigens. CONCLUSIONS: These results show the limitations of the A60 ELISA, and confirm the potencies of the glycolipid antigens in serodiagnosis of tuberculosis in HIV-positive and HIV-negative patients.

Diagnostic utility of the estimation of mycobacterial Antigen A60 specific immunoglobulins IgM, IgA and IgG in the sera of cases of adult human tuberculosis

SETTING

An ELISA assay based on mycobacterial Antigen A60 for the estimation of Mycobacterium-specific immunoglobulins in the serum has been used successfully for the rapid diagnosis of tuberculosis in studies done in the Western countries. There are hardly any similar large scale studies in India.

OBJECTIVE

To evaluate the utility of this ELISA test for rapid diagnosis of different clinical forms of tuberculosis in an adult Indian population.

DESIGN

ELISA test based on mycobacterial antigen A60 (Anda Biologicals, France) was used to estimate specific IgM, IgA and IgG antibodies in the sera obtained from 337 cases of tuberculosis and 131 controls in the population of Delhi (India).

RESULTS

Of the 131 controls, only 9.9% were positive for IgM, 7.6% for IgG, 6.1% for IgA and 9.9% when an IgA and IgG combination was considered. Of 122 cases of active pulmonary tuberculosis, 41% were positive for IgM, 86.8% for IgA, 88.5% for IgG and a very high positivity (98.3%) was seen when IgA and IgG estimations were combined. A relatively low seropositivity was observed in 25 cases of pleural tuberculosis. The corresponding figures in 130 cases of extrapulmonary tuberculosis were 22.3%, 68.4%, 73.8% and 86.15%. When 60 cases of pulmonary tuberculosis who had been successfully treated with antituberculosis drugs were analyzed the rates of seropositivity fell to 11.6%, 46.6%, 58.3% and 66.6% respectively.

CONCLUSION

Our findings point to a very good sensitivity (91.6%) and specificity (90.0%) of the test when combined IgA and IgG antibody titres are considered, to detect cases of adult tuberculosis. The role of IgM estimation can be restricted to the detection of cases of reactivation of tuberculosis.

Comparative cutaneous testing with purified protein derivative and the antigen complex A60 in vaccinated subjects and tuberculosis patients

Some 840 bacille Calmette-Guérin (BCG)-vaccinated healthy controls and tuberculosis patients from two Chinese hospitals were submitted to comparative skin tests with purified protein derivative of tuberculin (PPD; as reference) and with the antigen complex A60 from Mycobacterium bovis BCG. In a first trial, including 581 persons (185 healthy juveniles, 180 healthy adults and 216 tuberculosis patients), a limited dose of A60 (1 microgram) was used. Performance of the A60 test was similar to that of 5 I.U. PPD for controls (cut-off values = 5 mm induration diameter), but lower than that seen for tuberculosis patients (10 mm cut-off values). A second survey was conducted on 259 persons (109 recently revaccinated healthy persons, considered as tuberculin-negative in the first trial, and 150 tuberculosis patients), using a higher dose of A60 (2 micrograms) and the same dose of PPD (5 I.U.). Similar results were obtained with the two tests in all cases, thus supporting the possibility of PPD replacement by A60 in cutaneous testing. The pattern of induration diameter distribution in healthy subjects who took part in the first testing round (64% positively rate) was displaced to the inactivity side (with a peak at 5 to 9-mm diameter), in comparison with the second round (90% positivity rate and peak at 10-14 mm). This indicates a progressive fading of cellular immunity reactions after BCG vaccination. In tuberculosis patients, no correlation was found among the following three parameters: positivity at cutaneous testing (with PPD or A60), titer of anti-A60 mycobacterial immunoglobulins in blood (IgG titer higher than cut-off line) and presence of mycobacteria in sputum.

Composition and immunoreactivity of the A60 complex and other cell fractions from Mycobacterium bovis BCG

Surface static cultures of Mycobacterium bovis BCG contained cells embedded in an extracellular matrix, whose mechanical removal yielded free cells that were pressure disrupted and fractionated into cytoplasm and walls. Cell envelopes were either mechanically disrupted or extracted with detergents. Intracellular and extracellular fractions were analysed for proteins, polysaccharides, and antigen 6O (A60), a major complex immunodominant in tuberculosis. A60 was present in extracellular matrix, cytoplasm and walls: it represented a substantial portion of the proteins and polysaccharides of these fractions. While the protein/polysaccharide ratio varied according to the origin of A60 preparations, the electrophoretic patterns of A60 proteins (which accounted for the immunogenicity of the complex) remained unchanged. Western blots pointed to the proteins present within the 29-45 kDa range as the A60 components endowed with the highest immunogenicity level. Since the most heavily stained protein bands in SDS-PAGE patterns were located outside the region best recognized by antisera, a striking discordance was found between concentration and immunogenicity patterns of A60 proteins. The electrophoretic patterns of A60- and non-A60-proteins from cytoplasm were also different. A60 complexes in dot blots and some electrophoresed A60 proteins reacted with monoclonal antibodies directed against lipoarabinomannan (LAM), a highly immunogenic polymer of cell envelope. This contaminating compound was removed from A60 with organic solvents and detergents. SDS-PAGE and Western blot patterns of proteins from delipidated A60 were similar to those of native A60 proteins.

Humoral immune response against antigen 60 in BCG-vaccinated infants

An ELISA assay based on the A-60 antigen complex from Mycobacterium bovis BCG cytoplasm was used to detect anti-mycobacterial antibodies of different classes in the sera of 63 BCG-vaccinated infants during the 6-month post-vaccination period. The mean IgM and IgA levels increased, whereas the mean IgG level decreased after BCG vaccination. However, in a minority of cases only Ig levels were above the cut-off line: this was true for IgM in 11/63 (17%) cases and for IgA in 14/63 (22%) of cases but none of the tested infants was anti-A60 IgG ELISA positive. Fifty-two infants (83%) were tuberculin-positive eight weeks after vaccination, and no significant difference in mean antibody levels of tuberculin-positive and negative cases was observed, except for IgG (p < 0.05).

Extrapulmonary tuberculosis with paravertebral abscess formation and thyroid involvement

Extrapulmonary tuberculosis has a broad spectrum of clinical manifestations. Involvement of the thyroid gland has rarely been reported. We report a case in a patient with a non-tender swelling of the thyroid, whose symptoms, sonographic and scintigraphic features mimicked carcinoma. Initially the patient presented with back pain due to a paravertebral mass. Fine needle aspiration and culture of the aspirate both from the paravertebral mass and the thyroid ensured the diagnosis. Although seldom observed, tuberculosis should be kept in mind in the differential diagnosis of nodular lesions of the thyroid. The preponderant absence of thyroid dysfunction in mycobacterial thyroiditis is confirmed by this case.

Occurrence, in Crohn's disease, of antibodies directed against a species-specific recombinant polypeptide of Mycobacterium paratuberculosis

Sera from patients with Crohn's disease and control were analyzed by an enzyme-linked immunosorbent assay based on the Mycobacterium paratuberculosis-specific recombinant polypeptide a362. Anti-a362 immunoglobulin G (IgG) (P < 0.05) and IgA (P < 0.001) titers were higher in patients with Crohn's disease than in controls. A monomodal Gaussian distribution of anti-a362 IgA levels were found for controls, and a bimodal distribution was found for patients with Crohn's disease. An M. paratuberculosis etiology is suggested for the 36% of patients with Crohn's disease who had an anti-a362 IgA level higher than that of controls.

Immunological analysis of the components of the antigen complex A60 of Mycobacterium bovis BCG

The antigen complex of A60 of Mycobacterium bovis BCG was analyzed by different immunological techniques to assess its relevance to tuberculosis and the involvement of its components in the immune reactions elicited in humans by tuberculous infection. A60 is composed of about 30 components, of which 8 were identified by available monoclonal antibodies (lipoarabinomannan, a glycolipid, and proteins of 65, 40, 38, 35, 19, and 14 kDa). The majority (87.5%) of anti-mycobacterial antibodies in sera from tuberculosis patients was directed against A60. Western blot (immunoblot) analysis indicated that the majority of the highly antigenic proteins present in mycobacterial homogenates were components of the A60 complex. A small percentage (7.8%) of A60 epitopes proved to be species specific. Thus, A60 proteins of 66, 41, 38, 37, 35, 34, 32, and 22 kDa were found to contain B-cell epitopes specific for M. bovis and not shared by Mycobacterium leprae oR Mycobacterium avium.

Serological response of tuberculosis patients to antigen 60 of BCG

Two ELISA tests (IgG and IgM) for the serodiagnosis of tuberculosis, both based on antigen 60 (A60) of M. bovis BCG, were applied to 1,644 controls and patients to analyse the immune response in different forms of this infectious disease. Out of 200 healthy individuals, 148 being tuberculin--positive BCG-vaccinated adults, only 10 contacts--nurses of the pneumology department and laboratory technicians of the mycobacterial laboratory--were found positive for anti-A60 IgG. One quarter of hospitalized patients affected by non-tuberculous pneumopathies (194 in total) were found weakly positive for anti-A60 IgG. We suppose that these positive cases have suffered from inapperant infections and are in a "persistent state". Out of 344 cases of primary pulmonary tuberculosis, 88% were positive for anti-A60 IgG and 75% for the corresponding IgM. Among 97 cases of primary extra-pulmonary tuberculosis, 94% were found IgG positive and 33% IgM positive. The difference between active and inactive post-primary (chronic) tuberculosis was striking: about 100% of both pulmonary and extra-pulmonary cases (367 altogether) had high titers of anti-A60 IgG but IgM positivity was observed in only 15% of the cases, whereas in inactive and quiescent noncavitary tuberculosis (442 cases), 57% of the patients were weakly positive for anti-A60 IgG and none were positive for IgM. Kinetics of synthesis of anti-A60 IgG and IgM were analysed in primary and post-primary (chronic) active tuberculosis. The IgM tracing immune response to A60 was shorter and lower during primary tuberculosis as compared to post-primary tuberculosis. Our findings point to the high prognostic value of the A60- ELISA test for tuberculosis. Anti-A60 IgM mark initial stages of the disease or reactivation processes whereas anti-A60 IgG last longer than IgM and provide an evaluation of the intensity of the infectious process. Repeated serological tests allow monitoring of the course of the infection and the efficacy of therapy. The test is negative in healthy BCG-vaccinated persons (tuberculin-positive) and healed tuberculous infection cases. The combined use of both IgG and IgM tests helps in the correct diagnosis of "false positive" cases.

Composition and immunological properties of the protein fraction of A36, a major antigen complex of Mycobacterium paratuberculosis

TMA (thermostable macromolecular antigens) are major mycobacterial complexes present in all mycobacteria. We have purified A36, the TMA complex of M. paratuberculosis, the etiological agent of paratuberculosis (Johne's disease), and shown by the immune electron microscopy approach its presentation at the cell surface. The immunodominance of the A36 complex in Johne's disease was suggested by comparative ELISA analysis of infected bovine sera, using either A36 or M. paratuberculosis total soluble sonicate as antigens. The cross-reactivity of TMA complexes from different mycobacteria was evaluated by immunoenzymometric measurements. Percentage of shared epitopes was high for the couple M. paratuberculosis-M. avium, and somewhat lower for the couple M. paratuberculosis.-M. bovis. Immunological kinship between M. paratuberculosis and M. leprae was suggested by the finding that out of eleven anti-M. leprae monoclonals, four cross-reacted with A36 proteins. The specificity missing at the level of the whole A36 complex was sought at the level of its protein components. Comparative immunoblot analysis of electrophoresed A36 proteins indicated three of them to contain epitopes not shared by M. bovis proteins, and one of them to contain epitopes specific with respect to M. avium, M. bovis and M. phlei. The latter component, a 34-kDa protein, could be an ideal reagent for a serological test for Johne's disease, being immunodominant in infected cattle and endowed with species-specific epitopes.

Clinical usefulness of serological measurements obtained by antigen 60 in mycobacterial infections: development of a new concept

The humoral immune response occurring during mycobacterial infections was analysed with an ELISA test based on antigen 60. With tuberculosis, IgM antibodies indicate a primo-infection or a process of reactivation while IgG determinations allow an evaluation of the intensity of the infectious process. The test is also applicable to extrapulmonary tuberculosis, provided its sensitivity be adapted to these particular cases. This is particularly clear for tuberculous meningitis. The test is not species-specific and allows the detection of antibodies in atypical mycobacterioses and in leprosy patients. The final differentiation must be done by clinical examinations and cultures. In leprosy patients, IgM antibodies are detected nearly as frequently as IgG antibodies. In HIV-seropositive patients, the A60 seropositivity is correlated with a reactivation of former tuberculous infections and with primary tuberculous infections. At the AIDS stage, the A-60 seropositivity is due to atypical mycobacteria, with a better IgM than IgG response. Healthy people are negative in serology: the positive cases observed are due to inapparent infections gained by contact with an infectious focus. The seropositive cases observed in non-tuberculous hospitalized patients are restricted to some disease types, essentially lung infections (cystic fibrosis, cancer pneumopathies, sarcoidosis). Some patients have low levels of antibodies. This anergy may be traced to the formation of immune complexes or else to a weak avidity of the specific antibodies produced. This test should not be considered to be a diagnostic tool by itself. It should be used in conjunction with other diagnostic means that, together, allow the determination of a diagnosis.

Public health application of a serological test for tuberculosis: study of the incidence of inapparent infections among the employees of an Alsatian supermarket

A serodiagnostic test based on antigen 60 has been used to analyse the presence of IgG antibodies specific for mycobacteria, in the serum of the employees of a food supermarket. More than fourteen percent of the employees were seropositive, compared to 1.5% in a health adult population. The seropositives were restricted to those employees who were in direct contact with the customers.