Isolation, characterisation and kinetic studies on SEVA TB ES-31 antigen, a metallo-serine protease of interest in serodiagnosis.

BACKGROUND: SEVA TB Excretory secretory-31 (ES-31) antigen, a glycoprotein isolated from M. tb H37Ra culture filtrate, was found to be useful in the serodiagnosis of pulmonary tuberculosis (TB), extrapulmonary TB and in HIV-TB coinfection. Further, it has been shown to be a zinc containing serine protease. AIM: To isolate and purify SEVA TB ES-31 antigen from M. tb H37Ra culture filtrate and study of its enzyme properties and peptide sequence. METHODS: ES-31 antigen was purified from culture filtrate of M. tuberculosis H37Ra strain by ammonium sulphate precipitation, SDS-PAGE fractionation and FPLC. Protease activity of ES-31 antigen was studied using azocasein as substrate. ES-31 antigen was further fractionated by two dimensional polyacrylamide gel electrophoresis (2D PAGE) followed by LCMS-T analysis. RESULTS: Mycobacterial metallo-serine protease was purified 3096 fold from M. tb H37Ra culture filtrate protein. Purified enzyme showed optimum activity at pH 7.0 at 37 degrees C. Of the four substrates explored, the enzyme has shown maximum activity with azocasein and had a Km value of 0.01 mM with specific activity of 6250 x 10(-6) U/mg protein. Further, analysis of ES-31 antigen by 2D PAGE showed two protein spots (A and B). CONCLUSION: Kinetic studies on SEVA TB ES-31 protein, an immunogen with metallo serine protease activity are reported for the first time. Purified enzyme had a Km value of 0.01 mM with azocasein as substrate. Further, study on structure and biological role of serine protease will be of interest.

Detection of in vitro and in vivo released antigens of diagnostic interest in Mycobacterium tuberculosis by immunoblotting.

Identification of in vitro and in vivo released mycobacterial antigens are of considerable interest in diagnosis of Mycobacterium tuberculosis. Isolation of in vitro released antigen from M. tb excretory-secretory culture filtrate protein and in vivo released circulating tuberculous antigen from smear positive pulmonary tuberculosis sera by ammonium sulphate precipitation is reported. The antigens were resolved by SDS-PAGE and immunoblotting was performed using pooled serum of smear positive, smear negative pulmonary tuberculosis sera and normal sera to identify reactive tuberculous antigens. In vitro and in vivo released mycobacterial antigens showed reactivity at 100, 31, 43 and 20 kDa with smear positive and smear negative pulmonary tuberculosis patients. Further, the in vitro released antigen showed strong reactivity exclusively at 55 kDa antigen with smear positive and 24 kDa antigen with smear negative pulmonary tuberculosis sera. In vivo released antigen reacted exclusively at 170 and 16 kDa with smear positive and 19 kDa antigen with smear negative pulmonary tuberculosis patients. Antigens of 24 and 19 kDa which are reactive with sputum negative sera will be of diagnostic interest and need further study in patients with low bacillary load. The in vitro and in vivo released mycobacterial 100, 31,43 and 20 kDa antigens, reactive with patients sera are of diagnostic interest in tuberculosis.

Isolation and analysis of circulating tuberculous antigens in Mycobacterium tuberculosis.

BACKGROUND: Serological techniques like enzyme linked immunosorbent assay (ELISA) and immunoblotting are useful for detection of mycobacterial antigens of diagnostic importance in tuberculosis. AIM: To isolate and identify circulating tuberculous antigens reactive with sputum positive and sputum negative pulmonary tuberculosis (PTB) sera. METHODS: Circulating tuberculous antigen was isolated by ammonium sulphate fractionation from the sera of sputum positive and sputum negative (clinically and radiologically diagnosed) PTB cases. The circulating antigen fractions and individual patients' serum samples were resolved by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting was performed using anti M.tb sonicate IgG as a probe to detect antigens. RESULTS: Anti M.tb sonicate IgG was found to be reactive with mycobacterial proteins 170 kDa, 140 kDa, 85 kDa, 55 kDa, 43 kDa, 20 kDa and 16 kDa in the antigen fraction isolated from sputum positive tuberculosis sera by immunoblotting. However only 85 kDa, 55kDa, 43 kDa and 20 kDa antigenic proteins were found to be recognized by anti sonicate IgG in the antigen isolated from sputum negative sera. These observations were further confirmed by analysis of individual S+ and S- PTB serum by immunoblotting. CONCLUSION: Seroreactive studies of circulating tuberculous antigens showed the presence of 170 kDa, 140 kDa, 85 kDa, 55 kDa, 43 kDa, 20 kDa and 16 kDa protein antigens in sputum positive sera, while 85 kDa, 55 kDa, 43 kDa and 20 kDa antigens were found to be present in sputum negative PTB which need further evaluation for their use in serological diagnosis of tuberculosis.

Immunodiagnosis of bancroftian filariasis—Problems and progress.

The immunodiagnosis of bancroftian filariasis is a major challenge to the immunoparasitologist. Significant progress is yet to be made in developing convenient laboratory animal model and in in vitro cultivation of filarial parasites making it very difficult to obtain required amount of parasite material for research. Parasitological examination techniques are not useful in low microfilaraemia, occult or chronic .filarial infections. A precise and accurate immunodiagnostic technique is very much needed for successful filaria control programmes. Such a test will also avoid the need for laborious night blood examination in bancroftian filariasis. Due to comparatively easy availability, a good amount of work has been done to explore immunodiagnostic potential of heterologous filarial antigens isolated from Litomosoide carinii, Dirofilaria immitis, Brugia malayi, Setaria digitata, Setaria cervi and number of other filarial species. However, there has been limited or no significant success due to number of false negative and false positive reactions. Extensive study has also been made with antigens isolated from Wuchereria bancrofti microfilariae. Soluble antigens of microfilariae have been used in different immunological techniques such as skin test, counter immuno electrophoresis, indirect haemagglutination test, indirect fluorescent antibody test and enzyme linked immunosorbent assay. Fractionation of Wuchereria bancrofti microfilarial soluble antigens yielded mfS3e antigen fraction which was found to be highly reactive in microfilaraemia by enzyme linked immunosorbent assay, but the yield of the purified antigen was not sufficient enough to make it a practical proposition for large scale isolation of antigen. Wuchereria bancrofti microfilarial excretory-secretory antigens were found to be specific and highly sensitive requiring as little as 0·35 ng antigen protein per well in penicillinase enzyme linked immunosorbent assay for detection of filarial antibody. One ml of culture fluid was found to be sufficient for 400,000 tests. Field evaluation of this test showed that it can replace laborious night blood examination. Assay systems have been developed for detection of filarial antigen in serum, urine, hydrocele fluid and immune complexes using immunoglobulins from chronic filarial sera and antisera to excretory filarial antigens. Further purification of excretory-secretory antigens by affinity chromatography and production of monoclonal antibodies should hopefully give suitable reagents for use in sensitive assays such as enzyme immuno assay and immuno radiometric assay, providing an ideal assay system for detection of active filarial infection in the not too distant future.