Platelet Associated Fibrinogen and ICAM-2 Induce Firm Adhesion of Neutrophils under Flow Conditions

Abstract

SummarySurface-bound platelets support selectin-mediated rolling and β2-integrin-mediated firm adhesion of neutrophils (PMN) under flow conditions. We examined which ligands on platelets mediate this firm adhesion. Surface-bound platelets express ICAM-2 and GPIIbIIIa-bound fibrinogen, which are ligands for LFA-1 and MAC-1. In a well defined model for vessel wall injury, blood from an afibrinogenemic patient was perfused over ECM-coated coverslips to obtain fibrinogen-free platelet surfaces. At high shear rates, PMN-adhesion to fibrinogen-free platelet surfaces decreased compared to fibrinogen-containing controls. Under these conditions, firm adhesion and not rolling was blocked demonstrating the importance of fibrinogen in this process. In addition, MAC-1 and LFA-1 on PMN and ICAM-2 on platelets played a role in firm adhesion; the effect of blocking antibodies was most evident at high shear. The effects of fibrinogen depletion and ICAM-2 blocking were additive. In conclusion, multiple redundant ligands, like ICAM-2 and fibrinogen, induce firm and shear resistant PMN adhesion to platelets under flow conditions. Individually these ligands become critical at higher shear. Blocking of two or more interactions also interferes with low shear adhesion.

Neutrophil accumulation on activated, surface-adherent platelets in flow is mediated by interaction of Mac-1 with fibrinogen bound to alphaIIbbeta3 and stimulated by platelet-activating factor.

“…Hence, additional, unidentified ligands may contribute to PMN arrest and adhesion strengthening on activated platelets. This would be consistent with findings that platelets and fibrin are cooperative substrates for PMN adhesion under flow conditions (53), and may also explain why interactions of the fibrinogen ␥-chain and the Mac-1 region targeted by OKM1 mAb may not play a major role in transient adhesion of activated platelets to PMN in mixed suspension (11). Shear rates can be estimated in that system but shear forces acting on adhering cells are not exactly defined and may be relatively moderate.…”

Novel uses for anti‐platelet agents as anti‐inflammatory drugs

“…A principal b 2 -integrin present on activated platelets is intercellular adhesion molecule-2 (ICAM-2) (Diacovo et al, 1994). Platelet-derived ICAM-2 mediates lymphocyte-platelet adhesion via CD11a/CD18; and ICAM-2 may also contribute to neutrophil rolling and firm arrest, mediated by CD11b/CD18 under flow conditions (Kuijper et al, 1998). Glycoprotein-Iba (GPIba) has also been identified as a ligand for CD11b/CD18 (Simon et al, 2000), and leukocyte engagement of platelet GPIba via CD11b/CD18 has been shown to be critical for leukocyte accumulation in a mouse femoral artery injury model (Wang et al, 2005).…”

P-selectin Cross-links PSGL-1 and Enhances Neutrophil Adhesion to Fibrinogen and ICAM-1 in a Src Kinase-Dependent, but GPCR-Independent Mechanism

“…a M b 2 (Mac-1, CD11bCD18) is a principal neutrophil integrins, which, upon inflammatory challenges, undergoes conformational change for high affinity/avidity binding to its ligands, such as fibrinogen (Fg) and intercellular cell adhesion molecule-1 (ICAM-1, CD54). [8][9][10][11][12][13] The close proximity and the timing rendered by selectin-mediated leukocyte rolling are generally believed to facilitate b 2 -integrin activation by extracellular stimuli, such as interleukin-8 (IL-8), platelet activating factor (PAF), stromal cell-derived factor 1 (SDF-1, CXCL12) and several others. [14][15] They are released from and displayed on the activated endothelial lining of the vessel walls, which dynamically forms the "adhesive zone" with the contact site of rolling leukocytes in situ and locally activates leukocyte integrins in subseconds through pertussis toxin (PTX)-sensitive Gi-type heterotrimeric G-protein coupled receptors (GPCRs).…”