As measured by stability of pH, aggregability, and structure, concentrated platelets are better preserved for 72 hours at 4 C than at 22 C. While survival in vfvo, as determined with SlCr, of platelets stored at room temperature is extremely variable, survival of platelets stored at 4 C is invariably shortened to two to three days. In the treatment

Platelet interaction with exposed adhesive ligands at sites of vascular injury is required to initiate a normal hemostatic response and may become a pathogenic factor in arterial diseases leading to thrombosis. We report a targeted disruption in a key receptor for collageninduced platelet activation, glycoprotein (GP) VI. The breeding of mice with heterozygous GP VI alleles produced the expected frequency of wild-type, heterozygous, and homozygous genotypes, indicating that these animals had no reproductive problems and normal viability. GP VI null platelets failed to aggregate in response to type I fibrillar collagen or convulxin, a snake venom protein and known platelet agonist of GP VI. Nevertheless, tail bleeding time measurements revealed no severe bleeding tendency as a consequence of GP VI deficiency. Ex vivo platelet thrombus formation on type I collagen fibrils was abolished using blood from either GP VI null or FcR-␥ null animals. Reflection interference contrast microscopy revealed that the lack of thrombus formation by GP VI null platelets could be linked to a defective platelet activation following normal initial tethering to the surface, visualized as lack of spreading and less stable adhesion. These results illustrate the role of GP VI in postadhesion events leading to the development of platelet thrombi on collagen fibrils. IntroductionPlatelet membrane receptors interact with surface-bound adhesive ligands and, as such, become essential for hemostasis and thrombosis. 1 There are numerous unique receptors interacting with different adhesive ligands suggesting that a large opportunity exists for functional redundancy in platelet adhesion. However, an emerging theme of platelet biology is the relevance of different membrane receptors in different areas of the vasculature. 2,3 A specific example is the exclusive role for the platelet glycoprotein (GP) Ib-IX-V complex and von Willebrand factor in areas of the vascular system where flow rates and high shear occur, such as in small arteries and arterioles. 4 Thus, defining the physiologic relevance of an individual receptor and its ligand is an important aspect for understanding participation of the platelet in hemostasis and thrombosis.Among adhesive ligands of the extravascular matrix, collagen is a significant component with a number of known collagen receptors on the platelet surface. 5,6 One of the more recently characterized collagen receptors is GP VI. 7 The molecular cloning of GP VI revealed it to be a member of the immunoglobulin superfamily of type I transmembrane proteins. [8][9][10] The surface expression of GP VI requires the concomitant expression of the ␥-subunit of the FcR receptor (FcR-␥) and their association is functionally relevant as collagen binding to GP VI results in platelet signaling via the immunoreceptor tyrosine-based activation motif (ITAM) located in the FcR-␥ subunit. 8,[11][12][13][14] As with many of the platelet receptors, the in vivo relevance of GP VI was established prior to its description and recognition as a p...

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Abstract. We have identified monoclonal antibodies that inhibit human cell adhesion to collagen (P1H5), fibronectin (P1F8 or P1D6), and collagen and fibronectin (P1B5) that react with a family of structurally similar glycoproteins referred to as extracellular matrix receptors (ECMRs) II, VI, and I, respectively. Each member of this family contains a unique ¢t subunit, recognized by the antibodies, and a common [~ subunit, each of ~140 kD. We show here that ECMR VI is identical to the fibronectin receptor (FNR), very late antigen (VLA) 5, and platelet glycoproteins Ic-IIa and shall be referred to as FNR. Monoclonal antibodies to FNR inhibit lymphocyte, fibroblast, and platelet adhesion to fibronectin-coated surfaces. ECMRs I, H, and FNR were differentially expressed in platelets, resting or activated lymphocytes, and myeloid, epithelial, endothelial, and fibroblast cell populations, suggesting a functional role for the receptors in vascular emigration and selective tissue localization. Tissue staining of human fetal skin localized ECMRs I and II to the basal epidermis primarily, while monoclonal antibodies to the FNR stained both the dermis and epidermis. Experiments carried out to investigate the functional roles of these receptors in mediating cell adhesion to complex extracellular matrix (ECM) produced by cells in culture revealed that complete inhibition of cell adhesion to ECM required antibodies to both the FNR and ECMR II, the collagen adhesion receptor. These results show that multiple ECMRs function in combination to mediate cell adhesion to complex EMC templates and predicts that variation in ECM composition and ECMR expression may direct cell localization to specific tissue domains.ECENTLY, we identified a family of cell surface glycoproteins that mediate fibroblast adhesion to specific components of the extracellular matrix (ECM) ~ and are referred to as extracellular matrix receptors (ECMRs) I and II (Wayner and Carter, 1987). Monoclonal antibody to ECMR II (P1H5) specifically inhibited fibroblast (Wayner and Carter, 1987) and nonactivated platelet adhesion to collagen, while monoclonal antibody against ECMR I (P1B5) inhibited fibroblast adhesion to fibronectin (FN), collagen, and laminin (Wayner and Carter, T. J. Kunicki is an established investigator (83-186) of the American Heart Association.