Immunohistochemical study of inducible nitric oxide synthase [iNOS] in peritoneal Tuberculous granuloma

ABSTRACT

Nitric Oxide [NO] is important in host defense against Mycobacterium tuberculosis in rodents, but the presence of high-output NO production in human tuberculosis has been controversial. This study aimed to investigate iNOS expression by peritoneal macrophages in TB peritonitis and to gain insights into the structural properties of peritoneal TB granuloma. Peritoneal biopsies were obtained from 28 undiagnosed cases of ascites and examined histopathologically by H and E stain. Accordingly, specimens proved to be TB peritonitis were then immunohistochemically stained for iNOS, the macrophage marker CD68 and CD3 and CD20 as markers of T and B lymphocytes respectively. Eight control cases of normal peritoneum were included. TB peritonitis was diagnosed in 16 cases. TB granulomas were found in 9/16 cases [56%] and a diffuse granulomatous reaction was found in the remaining7/16 cases [44%]. Immunoreactivity to iNOS and CD68 were intensely expressed in macrophage rich TB granuloma and in the diffuse granulomatous TB reaction. Most Langhans cells [multinucleated giant cells] showed strong reactivity to both CD68 and iNOS. In TB granuloma, CD3[+] cells were found at the periphery with few CD20[4] cells in its center. Control cases showed complete negativity for iNOS, CDS, very small number of CD68 and/or CD20 cells. In TB peritonitis, an increased local expression of iNOS in granuloma associated macrophages of untreated patients indicating excess NO production in the active stage of this form of Tuberculosis. Further studies are needed to test the therapeutic implications of NO in different forms of TB