This protein recognizes C4b and C3b fragments that condense with cell-surface hydroxyl or amino groups when nascent C4b and C3b are locally generated during C4 and c3 activation. Interaction of daf with cell-associated C4b and C3b polypeptides interferes with their ability to catalyze the conversion of C2 and factor B to enzymatically active C2a and Bb and thereby prevents the formation of C4b2a and C3bBb, the amplification convertases of the complement cascade. Inhibits complement activation by destabilizing and preventing the formation of C3 and C5 convertases, which prevents complement damage. Monomer (major form) and non-disulfide-linked, covalent homodimer (minor form). Interacts with ADGRE5. Additional isoforms seem to exist. All the isoforms are widely expressed. GPI and TCS are the major forms, whereas SEC is minor and TCL is only present in trace levels. Has a shorter cytoplasmic region. Secreted. Has a longer cytoplasmic region. Has a longer cytoplasmic region. Has a shorter cytoplasmic region. Belongs to the receptors of complement activation (RCA) family.