Mechanism of glucocorticoid-induced depletion of human CD14+CD16+ monocytes

Healthy donors infused with high doses of glucocorticoids [GCs; methyl-prednisolone (MP); 500 mg/day for 3 days] suffer a selective depletion of the CD14+CD16+ monocytes such that these cells are reduced by 95% on day 5. In vitro studies revealed that at 11 h of culture in the presence of 10−5 M MP, no depletion was observed as yet, but a reduction by 80% was seen after 24 h. In dose-response analysis, MP still led to a 50% reduction of CD14+CD16+ monocytes at 10−7 M. Depletion could not be overcome by addition of the cytokines interleukin-1β or macrophage-colony stimulating factor, and it was independent of CD95. Depletion was, however, inhibited by the caspase 3,8 blocker z-Val-Ala-Asp, suggesting that cell death occurs in a caspase-dependent manner. Furthermore, blockade of depletion by RU-486 indicates that the intracellular GC receptor (GCR) is involved. Measurement of GCR by flow cytometry revealed a 50% higher level of expression in the CD14+CD16+ monocytes. Our studies show a selective depletion of CD14+CD16+ monocytes by GC treatment in vivo and in vitro, an effect to which the modestly increased level of GCR may contribute.