Immunohistochemical diagnosis of abdominal and lymph node tuberculosis by detecting Mycobacterium tuberculosis complex specific antigen MPT64

Abstract

Background: The aim of this study was to evaluate the diagnostic potential of immunohistochemistry using an antibody to the secreted mycobacterial antigen MPT64, in abdominal and lymph node tuberculosis.

Methods: We used formalin-fixed histologically diagnosed abdominal tuberculosis (n = 33) and cervical tuberculous lymphadenitis (n = 120) biopsies. These were investigated using a combination of Ziehl-Neelsen method, culture, immunohistochemistry with an antibody to MPT64, a specific antigen for Mycobacterium tuberculosis complex organisms. Abdominal and cervical lymph node biopsies from non-mycobacterial diseases (n = 50) were similarly tested as negative controls. Immunohistochemistry with commercially available anti-BCG and nested PCR for IS6110 were done for comparison. Nested PCR was positive in 86.3% cases and the results of all the tests were compared using nested PCR as the gold standard.

Results: In lymph node biopsies, immunohistochemistry with anti-MPT64 was positive in 96 (80%) cases and 4 (12.5%) controls and with anti-BCG 92 (76.6%), and 9 (28%) respectively. The results for cases and controls in abdominal biopsies were 25 (75.7%) and 2 (11.1%) for anti-MPT64 and 25 (75.7%) and 4 (22%) for anti-BCG. The overall sensitivity, specificity, positive and negative predictive values of immunohistochemistry with anti-MPT64 was 92%, 97%, 98%, and 85%, respectively while the corresponding values for anti-BCG were 88%, 85%, 92%, and 78%.

Conclusion: Immunohistochemistry using anti-MPT64 is a simple and sensitive technique for establishing an early and specific diagnosis of M. tuberculosis infection and one that can easily be incorporated into routine histopathology laboratories.

Figure 1

A: Percentage of stained cells by two antibodies in relation to organization of granuloma. B: Percentage of stained cells by two antibodies in relation to necrosis in granuloma.

Figure 2

Immunohistochemical staining in abdominal tuberculosis. A-C : Staining by anti-BCG in granuloma in intestinal wall, D-F : staining by anti-MPT64 in granuloma in intestinal wall. The area in square is magnified in subsequent sections, G : staining by anti-BCG in granuloma in peritoneum, H : diffuse staining of giant cells in peritoneum by anti-BCG, I : same giant cell as shown in H showing strong, granular staining with anti-MPT64.

Figure 3

Immunohistocheminal staining of lymph node tuberculosis. A : Staining by anti-BCG in organized granuloma. The central necrotic area is also showing staining, B : staining by anti-BCG in poorly organized granuloma. There is diffuse staining with background staining, C : The diffuse and weak staining of giant cell by anti-BCG, D : staining by anti-MPT64 in organized granuloma. The central necrotic area is not showing staining, E : staining by anti-MPT64 in poorly organized granuloma. There is granular staining in clear background, F : The strong and granular staining of giant cell by anti-MPT64.