Cytokines, phagocytes, and pentoxifylline

Phagocytic cells, such as polymorphonuclear neutrophils, monocytes, and macrophages, are essential for defense against infection caused by a variety of microorganisms. The mechanisms used by these cells to destroy microbes comprise a potent oxidative armamentarium including superoxide, hydrogen peroxide, and hypochlorous acid. In addition, granule contents such as proteolytic enzymes, lysozyme, lactoferrin, and myeloperoxidase are released into the phagosome to destroy ingested microorganisms. Inflammatory cytokines, such as tumor necrosis factor (TNF), interleukin-1 (IL-1), and IL-6, enhance the phagocytic and microbicidal activity of the cells and increase their stickiness. It has been demonstrated in a variety of animal and clinical studies that activated phagocytes can damage the host they are designed to protect, using the mechanisms described above. Alkylxanthines, including pentoxifylline, are potent inhibitors of this inflammatory damage by two major actions: (a) reduction of the production of inflammatory cytokines (especially TNF) by phagocytes stimulated with a variety of microbial products (e.g., endotoxin); and (b) reversal of the effect of these cytokines on phagocytes. Thus, pentoxifylline counteracts the following effects of inflammatory cytokines on phagocytes: increased adherence, shape change resulting in larger size and rigidity, increased oxidative burst, priming for an enhanced oxidative burst, increased degranulation, and decreased chemotactic movement. In addition, these activities synergize with the normal anti-inflammatory mediator adenosine. Alkylxanthines have the potential to be effective therapy for conditions in which inflammatory cytokines and phagocytes cause damage, including the sepsis syndrome, ARDS, AIDS, and arthritis.