Background Within the endoplasmic reticulum,
thiol isomerase enzymes modulate the formation and rearrangement of
disulfide bonds in newly folded
proteins entering the secretory pathway to ensure correct protein folding. In addition to their intracellular importance,
thiol isomerases have been recently identified to be present on the surface of a number of cell types where they are important for cell function. Several
thiol isomerases are known to be present on the resting platelet surface, including PDI, ERp5 and ERp57, and levels are increased following platelet activation. Inhibition of the catalytic activity of these
enzymes results in diminished platelet function and
thrombosis. Aim We previously determined that
ERp72 is present at the resting platelet surface and levels increase upon platelet activation; however, its functional role on the cell surface was unclear. We aimed to investigate the role of
ERp72 in platelet function and its role in
thrombosis. Methods Using HuCAL technology, fully humanized Fc-null anti-ERp72
antibodies were generated. Eleven
antibodies were screened for their ability to inhibit
ERp72 activity and the most potent inhibitory antibody (anti-ERp72) selected for further testing in platelet functional assays. Results and conclusions Anti-ERp72 inhibited platelet aggregation, granule secretion,
calcium mobilisation and
integrin activation, revealing an important role for extracellular
ERp72 in the regulation of platelet activation. Consistent with this, infusion of anti-ERp72 into mice protected against
thrombosis.