The effect of glucocorticoids on the expression of L-selectin on polymorphonuclear leukocyte

When active bone marrow release is induced by inflammatory stimuli, it is a ssociated with an increase in L-selectin expression on circulating polymorp honuclear leukocyte (PMN), This contrasts sharply with glucocorticoid-induc ed granulocytosis that is associated with decreased L-selectin expression o n PMN. The present study was designed to determine if the reduced L-selecti n expression observed after glucocorticoid treatment is the result of suppr ession of L-selectin synthesis in the bone marrow. New Zealand white rabbit s treated with dexamethasone (2.0 mg/kg, a single dose intravenously) were shown to have decreased L-selectin expression on circulating PMN 12 to 24 h ours after treatment (P < .01) with a return to baseline levels by 48 hours . When dexamethasone was administered 48 hours after the bane marrow PMN we re pulse labeled with the thymidine analogue, 5'-bromo-2'-deoxyuridine (Brd U), L-selectin expression on BrdU-labeled PMN released from the bone marrow was decreased (P < .01). Dexamethasone decreased L-selectin expression on segmented PMN in the bone marrow (P < .05) but not on PMN already in the ci rculation. We conclude that glucocorticoids decrease L-selectin expression on circulating PMN by downregulating L-selectin expression in the maturatio n pool of hone marrow and speculate that this is an important glusocorticoi d effect that influences the recruitment of PMN into inflammatory sites. (C ) 1999 by The American Society of Hematology.