Lymphokines Enhance the Capacity of Human Monocytes to Secrete Reactive Oxygen Intermediates

Open Access
Publisher Website
Google Scholar
Abstract
Supernatants from mitogen- or antigen-stimulated human blood mononuclear cells enhanced the capacity of human monocytes or monocyte-derived macrophages (MDM) to release H2O2 or O2̇̄ in response to phorbol myristate acetate or zymosan. The stimulatory effect of lymphokines (LK) lasted ∼5 d, regardless of the time of their addition. However, the magnitude of stimulation depended on whether LK were added to freshly explanted monocytes or to MDM. When LK were added on day 0 of culture, they enhanced MDM H2O2-releasing capacity ∼40% measured on day 3, when H2O2-releasing capacity in the controls was maximal. Addition of LK on day 2 retarded the decline in H2O2-releasing capacity normally seen by day 5, so that LK-treated cells released about twice as much H2O2 as the controls. Addition of LK to MDM that had already lost most of their H2O2-releasing capacity (e.g., on day 4-6) restored it to an average of 60% of the values seen with freshly explanted monocytes. In this case, LK-treated cells were about 12 times more active than cells incubated in medium alone. The effects of LK were dose- and time-dependent, with maximal effects requiring 3 d of exposure. The specific activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and myeloperoxidase, and the specific content of glutathione were not diminished in LK-treated MDM, suggesting that increased synthesis of H2O2 rather than decreased catabolism probably explained the greater release of H2O2 from LK-treated cells. In contrast, release of H2O2 was suppressed 93±4% by exposing monocytes for 4 d to hydrocortisone (50%-inhibitory concentration, 1.9±0.3 × 10−7 M). Thus, the oxidative metabolism of human mononuclear phagocytes can be markedly modulated in vitro: augmented by mediators released from lymphocytes during an immune response, and suppressed by antiinflammatory corticosteroids.