India accounts for a fifth of the world's new TB cases. Proteins encoded by RD1 have promise in serodiagnosis of TB. However, most studies have used healthy individuals as comparators. Sarcoidosis is not only a close clinical mimic of TB, it is also possibly in some way related to TB. In a recent meta-analysis we have reported that mycobacterial DNA has been isolated in up to 30% clinical samples of sarcoidosis. Here we evaluated the serodiagnostic potential of RD1 antigens in differentiating TB from sarcoidosis.
Sera from 10 sputum smear (for acid-fast bacilli) positive pulmonary TB (PTB) patients, 18 patients with pulmonary sarcoidosis and 20 PPD +/− healthy controls were subjected to single step ELISA with RD1 antigens (ESAT-6 and CFP10). Each sample was tested in triplicate.
Seven and five out of 10 patients with PTB showed immune reactivity to ESAT-6 and CFP10 respectively (i.e. mean optical density plus three standard deviations above that of healthy controls).Eight and 4 out of 18 patients with sarcoidosis showed reactivity to ESAT-6 and CFP10 respectively, with overall reactivity for any antigen being 9 out of 10 in PTB and 8 out of 18 patients (p=0.02) in sarcoidosis.
Patients with PTB show a significantly higher seroreactivity to RD1 antigens when compared to sarcoidosis.
The seropositivity to RD1 antigens in almost 45% of patients with sarcoidosis makes them a poor discriminator in differentiating TB from sarcoidosis. The positive results in patients with pulmonary sarcoidosis once again suggest a possible pathogenic role of mycobacterial antigens in sarcoidosis.
Ritesh Agarwal, No Financial Disclosure Information; No Product/Research Disclosure Information