CULTURE FILTRATE ANTIGENS IN TUBERCULOSIS DIAGNOSIS

摘要

Tuberculosis displays all of the principal characteristic features of a global epidemic disease and is rampant throughout the world. More than a century after its original development, the microscopic examination of sputum is still the only widely available diagnostic tool for identifying TB in most developing countries. Hence there is need for a rapid, sensitive and simple technique for the detection of Mycobacterium tuberculosis. Immunodiagnosis appears to be a promising approach for the diagnosis of pulmonary as well as extra-pulmonary tuberculosis. The sensitivity of a diagnostic test based on immunological approach depends on the nature of the diagnostic reagent viz., antigen or antibody employed, kind of diagnostic technique employed. A good serological assay should perform well in specific targeted populations, especially childhood TB, HIV positive and extrapulmonary TB. Unfortunately, the sensitivity of most serological tests falls with smear negativity - a finding attributed to the lower burden of organisms. In addition, the fact that large number of environmental bacteria have cross-reactive antigens and the antigens used so far are not very species- specific contrive to confuse the diagnosis. Hence the use of culture filterate antigens 85 kDa antigens which is known to be non-cross reactive even with the environmental mycobacterium is being used for the diagnosis of pulmonary and extra pulmonary tuberculosis. Culture filtrate of M. tuberculosis H37Rv is highly enriched with secretions, metabolites and degradative products of M. tuberculosis which may be proteins, lipids, carbohydrates and other metabolites. The metabolites of M. tuberculosis H37Rv in the culture filtrate are strong candidates for superior diagnosis of tuberculosis. The protein fraction was first separated from the CF based on the precipitation procedures. The protein fractions were then separated on SDS-PAGE with subsequent immunoblotting. Liposomes interchelated with CF 85 kDa and 38 kDa protein antigen complexes were employed in slide agglutination test for detection of specific antibodies in patient sera. The results are compared with that of smear test. The sensitivity and specificity of the test are of high degree and varied with the type and nature of specimens. Use of liposome agglutination technology employing culture filtrate immunodominant antigens has simplified the currently followed diagnostic procedures and considerably made the test economical, hence this test could be recommended even at primary health centres that lack in automation and skilled technicians.