NITRIC-OXIDE IN INFLAMMATION AND IMMUNE-RESPONSE

This short review deals with the role of a recently found signalling m olecule, nitric oxide (NO), in inflammatory and immune responses. NO r egulates inflammatory erythema and oedema and has cytotoxic action aga inst micro-organisms. In some instances (such as reperfusion injury) N O has cytoprotective properties. Production of large amounts of NO by activated macrophages accounts for their ability to suppress lymphocyt e proliferation. NO synthesis in lymphocytes is questionable but cytok ines secreted by activated lymphocytes regulate NO synthesis by macrop hages. Constitutive NO synthase is activated in neutrophils in respons e to inflammatory stimuli and NO has diverse, often biphasic effects o n neutrophil functions. Increased concentrations of nitrite and nitrat e (metabolites of NO) are present in arthritic joints. NO is synthesiz ed not only by migrated inflammatory cells but also by articular chond rocytes and inflamed synovial membrane. In the inflamed joint, NO regu lated the synthesis of several inflammatory mediators and functions of inflammatory cells. In addition, NO seems to mediate some destructive effects of proinflammatory cytokines such as interleukin-1. In conclu sion, NO regulates several humoral and cellular responses in inflammat ion, having both anti-inflammatory and proinflammatory properties depe nding on the type and phase of the inflammatory reaction.