Granulocyte apheresis in inflammatory bowel disease: possible mechanisms of effect.

We have studied the effects of granulocyte apheresis in 18 patients with ulcerative colitis and 6 with Crohn's disease who had failed to respond to conventional therapy. Patients were treated with weekly apheresis using a granulocyte removal column (GI, Otsuka Pharmaceutical Co., Ltd., London, U.K.). We found a mean reduction in circulating granulocytes of 1.29 x 10(9) cells/L with no significant alterations in red blood cell monocyte, total lymphocyte, absolute T-helper, or T-cytotoxic lymphocyte counts. There were no significant changes in complement levels or immunoglobulin subclasses. There was a significant increase in granulocyte adhesion and a reduction in L-selectin expression. The removal of granulocytes is unlikely to explain the effect of granulocytapheresis. The markedly increased expression of alpha(m) integrin/Mac-1 and low L-selectin expression alter the capability of granulocytes to migrate to sites of inflammation and may be responsible for the improvement observed in patients treated with granulocyte apheresis.