Red blood cell microparticles show altered inflammatory chemokine binding and release ligand upon interaction with platelets

BACKGROUND: Storage of red blood cells (RBCs) under standard blood bank conditions results in reduced structural integrity leading to membrane budding and release of microparticles. Microparticles express the blood group Duffy antigen known to bind multiple inflammatory chemokines, but the functional chemokine binding properties of microparticles are not known. STUDY DESIGN AND METHODS: We determined whether storage-induced microparticles show inflammatory chemokine binding through the expression of the Duffy antigen, comparing the binding properties to intact RBCs, and assessed microparticle interactions with platelets (PLTs) that release chemokines upon activation. RESULTS: Intact RBCs retained similar equilibrium dissociation constants for CCL2 (Kd = 7.4 +/- 0.9 nmol/L), CXCL8 (Kd = 7.9 +/- 1.0 nmol/L), and CXCL1 (Kd = 4.4 +/- 1.0 nmol/L) throughout storage. In contrast, microparticles increased in relative counts with storage, showed higher percentages of surface phosphatidylserine, and demonstrated impaired Duffy-dependent chemokine binding affinity with wider variability in dissociation constant for CXCL1(Kd = 362 +/- 328 nmol/L; range, 0.6-2000 nmol/L). The altered chemokine binding affinity of RBC microparticles was associated with a propensity to release ligand upon incubation with PLTs. Relative quantification of microparticles, based on criteria of glycophorin A expression and size, underestimated particle numbers with functional chemokine binding, suggesting that glycophorin A-negative particles and nanoparticles contribute to overall chemokine binding capacity. CONCLUSION: Microparticle burden in transfusates, as determined by functional chemokine binding, is considerable. Altered membrane properties of RBC microparticles enhance PLT interactions to increase inflammatory chemokine bioavailability in vitro.