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In the presence of Fell, 02' and H202 react in vitro to form hydroxyl radical (-OH). Considerable attention has been focused on the role of iron-catalyzed -0H production in phagocyte microbicidal activity and tissue damage. Early studies implied that both neutrophils (PMN [reviewed in reference 1]) and mononuclear phagocytes (2-9) generated -OH in the absence of an exogenous catalyst. However, the experimental systems used in these studies probably lacked specificity for -OH (1).Using spin trapping, generally considered the most specific technique for -OH ion, we did not find evidence for -OH production by human PMN in the absence of an exogenous iron catalyst (10, 11). Even then, -OH production appears to be inhibited by PMN secretion oflactoferrin and myeloperoxidase (MPO) (11-13). Monocytes do not possess lactoferrin (14) and have less MPO than PMN (15). Differentiation of monocytes to monocyte-derived macrophages (MDM) is associated with the loss ofMPO (15) and the acquisition oftartrate-resistant acid phosphatase (TRAP) (16). TRAP is an iron-containing enzyme, similar to uteroferrin, that may act as an -OH catalyst (17). The current work was undertaken to determine ifthese factors influenced the potential for -OH formation by mononuclear phagocytes . MONONUCLEAR PHAGOCYTES HAVE THE Brie,f Definitive ReportHumanmononuclearleukocytes and PMN were obtained by dex-. Monocytes and lymphocytes were separated by placing sterile petri dishes at 37°C, for 2 h. After washing, adherent monocytes were scraped into suspension . For MDM, monocytes were incubated in medium 199 (Univers of Iowa Cancer Center) with 13% autologous serum and gentamicin (50 gg/ml) for 5-7 MDM were released with trypsin and EDTA or by gentle scraping. In some cases, MDM were incubated in IFN-'Y (100 U/ml) for an additional 4 d.

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