The effect of interleukin-6 on L-selectin levels on polymorphonuclear leukocytes.

Interleukin-6 (IL-6) shortens the transit time of polymorphonuclear leukocytes (PMN) through the marrow and accelerates their release into the circulation. In contrast to other inflammatory stimuli, this response is associated with a decrease in L-selectin levels on circulating PMN. The present study was designed to determine the effect of IL-6 on L-selectin levels of PMN in rabbits. Recombinant human IL-6 (2 microg/kg) caused a decrease in L-selectin levels on circulating PMN 3 to 12 h after treatment (P < 0.05). L-selectin levels decreased on PMN already in the circulation for up to 4 h (P < 0.05), on PMN released from the marrow posttreatment for up to 12 h (P < 0.01) and on PMN in the marrow for up to 6 h (P < 0.05) after IL-6 treatment. We conclude that IL-6 decreases L-selectin levels on circulating PMN by demarginating PMN with low levels of L-selectin and by releasing PMN from the marrow with low levels of L-selectin. We postulate that this prolonged downregulation of L-selectin on circulating PMN could influence their recruitment into inflammatory sites.