Immunohistochemical study of INOS in peritoneal tuberculous granuloma

ABSTRACT

The human tuberculous granuloma provides the morphological basis for local immune processes central to the outcome of tuberculosis. Nitric Oxide [NO], produced by the inducible nitric oxide synthase [INOS], is important in host defense against Mycobacterium tuberculosis in rodents, but the presence of high-output NO production in human tuberculosis has been controversial. Because of the scarcity of information in human patients especially in peritoneal tuberculosis, the present study aimed to 1-investigate iNOS expression by peritoneal macrophages in TB peritonitis. 2- gain insights into the structural properties of peritoneal TB gronuloma. Laparoscoy was done for 28 patients with undiagnosed ascites and peritoneal biopsies were obtained and examined histopathologically by H and E stain. Accordingly, specimens proved to be TB peritonitis were then iminunohistochemically stained for iNOS, the macrophage marker CD 68 and CD 3 and CD 20 as markers of T and B lymphocytes respectively. Eight Control cases of peritoneum removed with surgically excised organ specimens [e.g. with excised tumors] 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 remaining 7/16 cases [44%]. Immunoreactivity to iNOS and the macrophage marker CD 68 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 CD 68 and iNOS. The expression intensity of iNOS and/or CD 68 was stronger in diffuse and premature-stage granulomas than in late-stage granulomas [caseating granuloma]. In TB granuloma, CD 3 cells were found at the periphery with few CD 20[+] cells in its center. While in diffuse granulomatous TB reaction, CD 3[+] lymphocytes were diffusely dispersed in the lesion with few CD 20[+] lymphocytes. Control cases showed complete negativity for iNOS, CD 3, very small number of CD 68 and/or CD 20 cells. In TB peritonitis, the distribution of different immune cells in the granuloma is similar to that described in pulmonary TB granulomas. An increased local expression of iNOS in granulomas 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