Incidence of inapparent active mycobacterial infections in France detected by an IgG serological test based on antigen 60

Rapid dot sputum and serum assay in pulmonary tuberculosis

A rapid direct sputum (Sp.) and/or antibody assay, based on immunoblotting and enzyme immunoassay is described. The test can detect mycobacterial antigens or antibodies in clinical specimens from pulmonary tuberculosis (TB) patients. In this study, 87 sputa, 87 sera and 40 paired sputa and sera were utilized from smear-positive and smear-negative, culture-positive patients; 59 sputa, 37 sera and 22 paired sputa and sera from nontuberculosis respiratory disease patients and 68 sera from healthy controls. The antigen detection in sputum by dot assay has 86.1% sensitivity on active tuberculosis patients, 92.9% specificity, 91.6% positive predictive value (PPV), 88.2% negative predictive value (NPV) and 10.3% error. The antibody assay has 83.6% sensitivity, 95.4% specificity, 94.4% positive predictive value, 85.6% negative predictive value and 11% error. The test performed on paired sputum and serum (Sr.) samples has a sensitivity of 93.3%, which rose to 96.1% on smear-positive and culture-positive patients, but the specificity decreased to 83% in sputum, whereas in serum it was 92%. The results of the assay, combined with clinical and radiological data, could form the basis for starting an earlier course of treatment for tuberculosis.

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.

Tuberculosis II: the failure of the BCG vaccine

BCG (bacille Calmette-Guerin) is an attenuated pathogen characterized by its capacity to induce cellular and humoral immune responses primarily against a nonpeptidic antigen, lipoarabinomannan. Immune responses against this substance contribute to the immunoprotection of the patient if the production of IL-2 and INF-gamma is not impaired. The most adequate production of INF-gamma and IL-2 is obtained by immunoreactivity against proteinic antigens. The formation of IgG-type antibodies and of cellular immunity against mycobacterial peptidic and proteinic antigens is an additional immunological response essential for a good protection. This is achieved by the BCG vaccine in only a small proportion of the vaccinees. A vaccine adjuvant that also finds application as an immunotherapeutic agent is composed of proteinic antigens such as sonicates of Mycobacterium vaccae and antigen 60 of Mycobacterium bovis. These enhance the beneficial Th1-pole of the immune response. In addition, A60 induces the formation of antibodies against species-specific proteinic antigens. Despite the questioning of its innocuousness and efficacy, the BCG vaccine was imposed worldwide in 1950 by medical and political organizations that showed no concern for these questions. The contemporary structures of research administration in this area make it unlikely that the efficacious means recently developed to complement the action of the vaccine and of chemotherapies to face the surge of tuberculosis (TB) will be readily adopted.

Mycobacterial infections: are the observed enigmas and paradoxes explained by immunosuppression and immunodeficiency?

The enigmas and paradoxes observed in tuberculous patients, in Bacille Calmette-Guérin-vaccinated people and in Bacille Calmette-Guérin-treated cancer patients have been examined, in an attempt to explain them through the mechanisms of immunodeficiency and immunosuppression. A dual effect is postulated: an immunosuppression induced by the infecting mycobacteria that adds to a pre-existing or emerging state of immunodeficiency of the infected individual. The immunological cellular and humoral anergies observed at the beginning of a tuberculous therapy are usually lifted after the first two weeks of treatment. This restoration of immune responsiveness may be attributed to the destruction or to the growth inhibition of immunosuppressive mycobacteria. The observation that drugs cytocidal in vitro do not always sterilize the patients under treatment whereas bacteriostatic drugs do, may find an explanation in the dual immunosuppression induced by cytocidal drugs and mycobacteria. The fact that Bacille Calmette-Guérin applied as an immunotherapy to residual cancer has either a favorable or an unfavorable action may be due to the immunosuppressive activity attached to some Bacille Calmette-Guérin strains and to some cancers. The variable protective activity of Bacille Calmette-Guérin vaccines may be due to the immunological status of the vaccinated people and the compositional differences between strains. The protective activity of subunit vaccines in experimental models can be attributed to the elimination of immunosuppressive factors present in whole killed mycobacteria.

Value of ELISA using antigen 60 for the diagnosis of tuberculosis in children

We evaluated the possible value of enzyme-linked immunosorbent assay (ELISA) using antigen 60 (A60) for improved diagnosis of tuberculosis in children. Results obtained in 31 children with active tuberculosis and in 16 patients with tuberculous infection without disease were compared with the results of 198 control subjects with no mycobacterial disease. In control children, anti-A60 IgG increased with age and the optical density (OD) in ELISA assays rose from .079 +/- .053 (OD +/- SD) in children younger than 5 years old to 0.146 +/- 0.082 OD in children older than 5 years. In control subjects younger than 2 years old, IgG OD values were significantly higher in BCG-vaccinated children than in nonvaccinated children. At a chosen specificity of 98 percent, a positive serodiagnosis was observed in 68 percent of children with clinically active tuberculosis. In these children with active disease, smears were positive in only 26 percent of cases and mycobacterial cultures yielded the organism in 45 percent of cases. None of the infected children without disease had high IgG OD values. IgM measurements were also evaluated. Mean values from control and diseased children overlapped, leading to a low sensitivity (19 percent) in children with clinically tuberculosis active. We conclude that anti-A60 IgG measurement is a rapid and low-cost technique that enhances the diagnosis of clinically active tuberculosis in children and may distinguish recent infection without disease from infection with disease.

Sero-diagnosis of tuberculosis with A60 antigen enzyme-linked immunosorbent assay: failure in HIV-infected individuals in Ghana

In order to assess the diagnostic usefulness of the A60 (ANDA Biological, Strassbourg, France) sero-diagnostic enzyme-linked immunosorbent assay (ELISA) kit for tuberculosis in Africa, sera of 53 pulmonary smear-positive tuberculosis (TB) patients, 30 apparently healthy control subjects and 6 AIDS suspects were sampled in Agogo Hospital in the forest area of Ghana. These sera were analyzed for antibodies to HIV-1 and HIV-2, and IgG-antibodies to the A60 BCG-antigen, while the non-HIV individuals were tested for total IgG levels. One healthy control subject, all of 6 AIDS suspects and 7 of the TB patients has HIV infections. In the non-HIV TB group, the sensitivity and specifity of the A60 ELISA was 78% and 86%, respectively, which was much poorer than expected from published reports about the A60 test. The A60 test failed, completely however, to discriminate between TB and non-TB in the HIV-positive group. In the non-HIV groups, total IgG levels were significantly higher in TB patients than in controls. It seems that the usefulness of the A60 ELISA test to diagnose tuberculosis is very limited in this high-incidence area, and that it seems to be of no value in patients infected with HIV.