Characterization of small and large human peripheral blood monocytes: Effects of in vitro maturation on hydrogen peroxide release and on the response to macrophage activators

Human peripheral blood monocytes (HPBM) isolated from normal donors by centrifugal elutriation were divided into two populations according to volume. (Median volumes of small monocytes (SM) and large monocytes (LM) were 255 μm³ and 280 μm³, respectively). H₂O₂ production was determined during in vitro culture and in response to bacterial lipopolysaccharide (LPS), and to recombinant human interferon-γ (rIFN-γ). On day 1, H₂O₂ production by LM was significantly greater than that by SM. In vitro culture of SM resulted in an augmented ability to produce H₂O₂. By day 3, SM were the major H₂O₂ producers. Freshly isolated SM and LM, exposed for 24 hr to LPS and rIFN-γ, showed different patterns of activation. Both SM and LM responded to LPS, with LM responding maximally at lower doses than SM. Only SM showed a significant augmentation of H₂O₂ production with rIFN-γ treatment. We also assessed the effect of in vitro culture with activation. SM but not LM showed an increased H₂O₂ to LPS and rIFN-γ after 7 days in culture. Continuous exposure of SM to rIFN-γ resulted in maximal H₂O₂ production at day 3 of culture; this pattern was not seen for LPS. The production of H₂O₂ by HPBM is related to in vitro maturation. The enhanced H₂O₂ production by HPBM upon exposure to rIFN-γ may be related to the induction of in vitro maturation.