Differentiation of polymorphonuclear neutrophils in patients with systemic infections and chronic inflammatory diseases: evidence of prolonged life span and de novo synthesis of fibronectin.

Polymorphonuclear neutrophils (PMN) are considered to be short-lived, terminally differentiated cells undergoing spontaneous apoptosis if not appropriately stimulated. In patients with systemic infections and inflammatory disease, however, PMN have an extended life span and acquire new surface receptors and functions. Expression of CD64, the high-affinity receptor for immunoglobulin, has been found, and functionally active elastase and surface-associated fibronectin as well. The latter is of particular interest since fibronectin is known as a multifunctional, multimodal extracellular matrix protein, participating in cell adherence, cell signaling, and cell cycle control. To study the surface-associated fibronectin further, PMN of healthy donors were cultivated to induce de novo synthesis of fibronectin. PMN produced fibronectin, which remained associated with the cell surface, where it was partially cleaved. PMN derived fibronectin exhibited a rare splice pattern: predominantly fibronectin containing the extradomain B (EDB) was generated, but evidently no IIICS domain; the latter is known as a receptor for beta1 integrins. How the presence of EDB affects the properties of fibronectin is not yet understood. Studies with recombinant EDB have failed to show a membrane-binding site or a direct participation of EDB in the adhesion process. The function of PMN-associated fibronectin is still under investigation. The rapid cleavage by surface-associated proteases suggests that fibronectin acts as a tightly regulated adhesion protein, and probably also as a precursor molecule for fibronectin-derived biologically active mediators.