A low molecular weight ES-20 protein released  in vivo and  in vitro with diagnostic potential in lymph node tuberculosis

Purpose: To determine role of antigens released in vivo and in vitro in immunodiagnosis of tuberculosis (TB).
Methods: In vivo released circulating tuberculosis antigen (CTA) was obtained from TB sera by ammonium sulphate precipitation and in vitro released excretory-secretory (ES) antigens from Mycobacterium tuberculosis culture filtrate. CTA and ES antigens were fractionated by SDS-PAGE and electro-eluted gel fractions were analysed for antigen by ELISA.
Results: Low molecular weight proteins CTA-9 and ES-9 showed high titre of antigen activity. To explore the diagnostic potential of low molecular weight ES antigen, M. tuberculosis ES antigen was further fractionated by gel filtration chromatography followed by purification on anion exchange column using fast protein liquid chromatography and a highly seroreactive ESG-5D (ES-20) antigen was obtained. Competitive inhibition showed that CTA-9 and ES-9 antigens inhibit the binding of ES-20 antigen to its antibody. Seroanalysis showed sensitivity of 83 and 80% for ES-20 antigen and antibody detection, respectively, in pulmonary TB and 90% in lymph node TB.
Conclusions: Seroreactivity studies using M. tuberculosis ES-20 antigen showed usefulness in detection of TB; in particular, lymph node TB.

Keywords
Circulating tuberculosis antigen, diagnosis, ELISA, excretory-secretory antigen, tuberculosis