Detection of shed CD31, diagnosis of atherothrombosis and autoimmune disorders, and methods for analyzing signaling pathways

A method for detecting a shed ectodomain of a CD31 transmembrane protein among soluble forms of said transmembrane protein in a biological sample, wherein said soluble forms include a soluble splice variant of said transmembrane protein and optionally said shed ectodomain, which comprises the steps of:

• a) providing a first type of bead linked to a first discriminating antibody, which antibody specifically binds to an epitope located in a region that is present both on said shed ectodomain and on said splice variant;
• b) providing at least one second type of bead linked to a second discriminating antibody, which antibody specifically binds to an epitope located in a region that is either present on said shed ectodomain and absent from said splice variant, or present on said splice variant and absent from said shed ectodomain;
• c) providing a signaling ligand, which signaling ligand is a fluorescently-labelled ligand which specifically binds to a region that is present both on said shed ectodomain and on said splice variant;
• d) contacting said antibodies and said signaling ligand with a biological sample likely to contain said soluble forms of said transmembrane protein;
• e) for each type of bead, measuring a signal obtained with said florescent label by flow cytometry;
• and
• f) comparing the signal obtained for each type-bead;
• wherein a difference in the signals measured at step (e) for each type of bead indicates that the biological sample comprises said shed ectodomain of the CD31 transmembrane protein, and wherein the first type of bead and the at least one second type of bead are distinguishable from each other.