Nitric oxide modulates interleukin-1β and tumour necrosis factor-α synthesis, and disease regression by alveolar macrophages in pulmonary tuberculosis

Pretreatment with nitric oxide synthase (NOS) inhibitors profoundly increases mortality, bacterial burden and pathological tissue damage in mice infected with Mycobacterium tuberculosis. Nitric oxide (NO) production is enhanced in alveolar macrophages (AM) of tuberculosis (TB) patients. Interleukin (IL)-1β and tumour necrosis factor (TNF)-α released from AM are involved in the immune response to mycobacterial infection. The aim of the present study was to examine whether NO is implicated in IL-1β and TNF-α synthesis by AM and related to the resolution of disease activity in TB patients. Purified AM were retrieved by bronchoalveolar lavage from TB patients and normal subjects, and cultured in the presence or absence of a NO inhibitor, N^G-monomethyl-L-arginine (L-NMMA). The release of IL-1β and TNF-α, and their mRNA expression were determined by enzyme-linked immunosorbent assay (ELISA) and northern analysis, respectively. The level of nitrite released into the culture medium was determined. The rate of disease regression was evaluated by serial chest radiography. The release of nitrite, IL-1β and TNF-α was much greater from AM of TB patients than normal subjects. N^G-monomethyl-L-arginine inhibited the production of nitrite as well as IL-1β and TNF-α in TB patients. The mRNA expression for IL-1β and TNF-α was upregulated in TB patients and was depressed by L-NMMA. Immunocytochemistry using a monoclonal antibody against nuclear factor-κB (NF-κB) subunit p65 showed NF-κB was highly expressed and translocated to the nuclei of AM in TB patients, and was inhibited by L-NMMA. An inhibition of NF-κB by pyrrolidine dithiocarbamate attenuated IL-1β and TNF-α synthesis. More generation of NO from cultured AM increased the disease regression in TB patients. We conclude that the enhanced NO generation by AM of TB patients may play an autoregulatory role in amplifying the synthesis of pro-inflammatory cytokines, probably through the activation of NF-κB. Nitric oxide may also play an important role in resistance to M. tuberculosis infection.