The aim of the study was to evaluate the diagnostic potential of immunohistochemistry using an antibody to the secreted mycobacterial antigen MPT64, specific for Mycobacterium tuberculosis complex organisms, on formalin-fixed biopsies from patients with pleural tuberculosis (TB) from a high TB and HIV endemic area.
Methods and Results
Pleural biopsies from 25 TB cases and 11 non-TB cases were studied. Ziehl-Neelsen staining for acid-fast bacilli and immunohistochemistry with anti-MPT64 and anti-Bacille Calmette-Guérin (BCG) antibodies was performed. Nested polymerase chain reaction (N-PCR) for IS6110 was performed for comparison. Acid-fast bacilli were detected in only 2 cases and 3 biopsies showed granulomas with caseous necrosis. Immunostaining with anti-MPT64, anti-BCG, and N-PCR were positive in 20 (80%), 12 (48%), and 16 (64%) of the cases, and 0, 3 (27%), and 2 (18%) of the non-TB controls, respectively. The diagnostic validity of immunohistochemistry was calculated by comparison with N-PCR–positive TB cases and N-PCR–negative non-TB controls. The sensitivity of immunohistochemistry with anti-MPT64 and anti-BCG were 81% and 56% respectively, and the corresponding specificities were 100% and 78%.
Detection of the MPT64 antigen by immunohistochemistry improves the diagnosis of TB pleuritis caused by M. tuberculosis complex organisms in patients living in HIV-endemic areas with atypical histology and negative staining for acid-fast bacilli.