Complement-dependent and cell-dependent antiplatelet humoral antibody in sera from multi-transfused patients

Sera from eight multi-transfused patients, who were resistant to platelet trans-fusions from allogeneic donors, were tested for antiplatelet humoral antibody. Complement-dependent cytotoxic humoral antibody against platelets was found in sera from six of eight patients. Cell-dependent cytotoxic humoral antibody against platelets was found in sera from four of seven of these patients. Sera from two patients had cell-dependent antiplatelet activity but no detectable complement-dependent antiplatelet activity. Results of this study argue that both complement-dependent and cell-dependent humoral immunity may be important pathways for in vivo resistance to platelets.