['In addition to its anticoagulant properties, heparin has anti-inflammatory effects, the molecular and mechanistic bases of which are incompletely defined.', 'The current studies were designed to test the hypothesis that heparin abrogates the expression or function of leucocyte-endothelial adherence molecules which are fundamental to the acute inflammatory response.', 'The effects of heparin on tumour necrosis factor alpha (TNF-alpha) induced leucocyte rolling, adhesion, and migration as well as vascular permeability were assessed in rat mesenteric venules using intravital microscopy. Expression of adhesion molecules was quantitated using a double radiolabelled monoclonal antibody (mAb) binding technique in vivo (P-selectin, intercellular cell adhesion molecule type 1 (ICAM-1), and vascular cell adhesion molecule 1 (VCAM-1)) or flow cytometry (CD11a, CD11b, and L-selectin). Ex vivo binding of heparin to neutrophils was assessed by flow cytometry.', 'TNF-alpha induced a significant increase in leucocyte rolling, adhesion, and migration, and vascular permeability, coincident with a significant increase in expression of P-selectin, ICAM-1, and VCAM-1. Ex vivo assessment of blood neutrophils showed significant upregulation of CD11a and CD11b and significant downregulation of L-selectin within five hours of TNF-alpha administration. Heparin pretreatment significantly attenuated leucocyte rolling, adhesion, and migration but did not affect expression of cell adhesion molecules or vascular permeability elicited by TNF-alpha administration. Binding of heparin was significantly increased on blood neutrophils obtained five hours after TNF-alpha administration. Preincubation with an anti-CD11b mAb but not with an anti-CD11a or anti-L-selectin antibody significantly diminished heparin binding ex vivo.'] Does heparin attenuate TNF-alpha induced inflammatory response through a CD11b dependent mechanism?