Upregulation of inducible nitric oxide synthase and cytokine secretion in peripheral blood monocytes from pulmonary tuberculosis patients

SETTING: Peripheral blood monocytes (PBM) are the main source of alveolar m acrophages, which have an upregulation of inducible nitric oxide synthase ( iNOS) in pulmonary tuberculosis (TB). TNF-alpha and IL-1 beta are thought t o be involved in the immune response to mycobacterial infection. OBJECTIVE: To identify whether iNOS expression and cytokine release of PBM are upregulated and have a connection in TB infection. DESIGN: The expression of iNOS immunoreactivity on PBM from TB patients and normal subjects was measured by loading with anti-macrophage iNOS polycolo nal primary antibody analyzed by Row cytometry. Expression of iNOS mRNA in PBM was detected by RT-PCR. The spontaneous generation of nitrite and cytok ines (IL-1 beta and TNF-alpha) by cultured monocytes was also determined. RESULTS: Compared to normal subjects, iNOS immuno-reactivity, the capacity for spontaneous nitrite generation and the level of TNF-alpha or IL-1 beta secretion of PBM were significantly higher in TB patients. The amount of ni trite, TNF-alpha and IL-1 beta released from PBM of TB patients was inhibit ed by NG-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of NOS. Th e level of iNOS immunoreactivity on PBM was highly correlated with nitrite generation both in all the subjects studied and in TB patients alone. Spont aneous TNF-alpha production showed a stronger correlation with nitrite prod uction than with IL-1 beta. CONCLUSION: The NO and cytokine synthase activities of monocytes appear to be concomitantly upregulated in response to mycobacterial infection. The en hanced NO generation by monocytes in TB patients may play an autoregulatory role in amplifying the synthesis of proinflammatory cytokines.