A monoclonal antibody to leukocyte integrin CD11b inhibits leukocyte and platelet activation induced by shear stress

Leukocyte-platelet interactions are mediated by cellular antigens and result in cellular activation and formation of aggregates composed of leukocytes and platelets. Rheological mechanisms play a key role in cellular activation phenomena. We have investigated the activation of leukocytes and platelets induced by shear stress, and the effects of monoclonal antibodies to CD11b and CD62P on platelet-leukocyte interaction. Flow cytometry was employed to asses leukocyte and platelet activation. Profiles in forward and side scatter, and dual color fluorescence were used to detect the presence of heterotypic aggregates. Shear stress induced activation of both leukocytes and platelets (p < 0.05 vs. control) and favored the formation of small aggregates (p < 0.05 vs. control). Incubation of blood with anti-CD11b inhibited expression of CD62P and increased the number of aggregates but reduced their size. Anti-CD62P did not modified expression of CD11b neither change the heterotypic aggregation pattern. Our results suggest that CD11b may play an important role in leukocyte-platelet cross-talk and indirectly influence platelet-platelet interaction under shear stress conditions.