Formation of platelet-leukocyte aggregates in inflammatory bowel disease

Objectives: Formation of platelet-leukocyte aggregates (PLAs) is increased in several inflammatory and thrombotic conditions. This may result from and enhance platelet and neutrophil activation and could contribute to the inflammatory process in inflammatory bowel disease (IBD). We investigated platelet-leukocyte aggregation in patients with IBD and its relation to treatment, disease activity and platelet and neutrophil activation. Methods: PLAs, platelet activation (P-selectin expression) and neutrophil activation (L-selectin expression) were assessed 30 and 180 minutes after drawing blood into EDTA/citrate-theophylline-adenosine and dipyridamole, a novel anticoagulant, using fluorescent antibodies to CD45 (for leukocytes), CD42a (for platelets), CD62P (P-selectin) and CD62L (L-selectin) and flow cytometry. Platelet activation was also measured using the ADVIA 120 hematology analyser. Results: Samples from 67 patients with IBD measured within 30 minutes had a higher platelet count (P < 0.001), more platelets expressing P-selectin (P = 0.01), and more PLAs (P<0.01) than from 20 healthy controls and more PLAs (P < 0.05) than from 9 controls with inflammatory arthropathies. 1131) patients on thiopurines had fewer PLAs than those not taking them (P < 0.05); corticosteroids and aminosalicylates had no such effects. Incubation for 180 minutes increased the number of platelets expressing P-selectin (P < 0.0001), and the number of PLAs (P < 0.0001). The PLAs correlated with the number of platelets expressing P-selectin before (r=+0.40, P < 0.001) and after (r=+0.66, P < 0.0001) incubation. Conclusions: The number of PLAs is higher in patients with IBD than in healthy and inflammatory controls, but their numbers are lowered by thiopurines. Increased PLA formation may in part be due to increased platelet activation and could be pathogenic in IBD.