Monocytes lack lactoferrin and have much less myeloperoxidase than neutrophils. They also acquire a potential catalyst for .OH production (tartrate-resistant acid phosphatase) as they differentiate into macrophages. Consequently, the nature of free radicals produced by these cells was examined using the previously developed spin-trapping system. When stimulated with either PMA or OZ neither monocytes nor monocyte-derived macrophages (MDM) exhibited spin trap evidence of .OH formation. Pretreatment with IFN-gamma failed to induce MDM .OH production. When provided with an exogenous Fe+3 catalyst, both stimulated monocytes and MDM, but not PMN, exhibited sustained .OH production, presumably due to the absence of lactoferrin in mononuclear phagocytes. Sustained production of .OH could contribute to the microbicidal activity of mononuclear phagocytes as well as inflammatory tissue damage under in vivo conditions where catalytic Fe+3 may be present.

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