Modulation of polymorphonuclear leukocytes function by nitric oxide

Recognition of the endothelium-derived relaxation factor as nitric oxide (N O) gave rise to an impression that NO was synthesised only by the endotheli al lining of the vessel wall. Later it was found that NO is synthesized con stitutively by the enzyme nitric oxide synthase (NOS) in various cells. How ever, inflammatory cytokines can induce NOS (known as inducible NOS [iNOS]) activity in all the somatic cells. Blood cells, such as eosinophils, plate lets, neutrophils, monocytes, and macrophages, also synthesize NO. Among th em, polymorphonuclear leukocytes (PMNs) constitute an important proportion and are also the major participants in a number of pathological conditions with suggestive involvement of NO. PMNs can synthesize NO at rates similar to endothelial cells, thus suggesting the importance of PMN-derived NO in v arious physiological and pathological conditions. Most of the studies so fa r focus on the peripheral PMNs, while studies on PMNs after emigration are limited, thus warranting systematic studies on PMNs from both sources. The role of the endothelial NOS (eNOS) and functions of NO derived from the end othelial cells has been studied extensively. However, understanding of the PMNs NOS and its regulatory role in their function is unraveling. The prese nt review summarizes the modulatory role of NO on PMNs functions and points out the discrepancies relating to presence of NOS in PMNs. This informatio n will be helpful in understanding the importance of NO in physiological an d pathological conditions associated with PMNs. (C) 2000 Elsevier Science L td. All rights reserved.