ENHANCED COMPLEMENT SUSCEPTIBILITY OF AVIDIN BIOTIN-TREATED HUMAN ERYTHROCYTES IS A CONSEQUENCE OF NEUTRALIZATION OF THE COMPLEMENT REGULATORS CD59 AND DECAY-ACCELERATING FACTOR

Biotinylation of erythrocytes (E) followed by avidin cross-linking at specific sites has been suggested as a novel means of drug delivery. U pon avidin cross-linking, biotinylated E become complement-activating and highly susceptible to complement lysis, thus bringing about releas e of entrapped drug. We set out to examine the mechanisms of this biot in-avidin-induced lytic susceptibility, focusing on the effects of bio tinylation and avidin cross-linking on the major E complement regulato ry molecules, decay accelerating factor (DAF) and CD59. We demonstrate here that biotinylation of E, which does not render them complement a ctivating, partially inhibits DAF but has little effect on CD59. Subse quent cross-linking with avidin causes complete inhibition of DAF and near complete loss of CD59 activity. Following cross-linking, DAF and CD59 become associated in high molecular mass avidin-containing comple xes on the membrane. Incorporation of physiological amounts of CD59 in to the membranes of biotinylated and avidin cross-linked E is sufficie nt to render these cells resistant to complement lysis whereas incorpo ration of DAF has relatively little effect. An understanding of the mo lecular mechanisms underlying complement susceptibility of biotin-avid in treated E should allow a rational design of strategies for drug del ivery using E or other large, potentially complement-activating carrie rs.