ISOLATION AND CHARACTERIZATION OF HUMAN ANTIOXIDIZED LDL AUTOANTIBODIES

Autoantibodies to oxidized LDL have been reported in normal subjects a nd in patients with arteriosclerosis, but their possible pathogenic ro le is not yet well defined. One important problem is the existence of contradictory data reported by different groups concerning the associa tions between antioxidized LDL autoantibodies and the presence or prog ression of arteriosclerotic lesions. Such contradictions led us to dec ide to isolate and characterize antioxidized LDL antibodies by affinit y chromatography with the use of oxidized LDL cross-linked to Sepharos e. Antioxidized LDL antibodies were isolated from selected serum sampl es obtained from eight subjects. Seven of them (six patients and one c ontrol subject) had high levels of antioxidized LDL antibody during sc reening. The other subject, a healthy volunteer, had a low level of an tibody. All purified antibodies contained IgG (of subclasses 1 and 3) as the predominant isotype and were primarily specific for oxidized LD L but showed some cross-reactivity with malondialdehyde-modified LDL a nd native LDL. Two of the purified antibodies cross-reacted with cardi olipin. We determined average dissociation constants for the antioxidi zed LDL antibodies purified from five individuals, which varied betwee n 2.4x10(-7) and 7.5x10(-7) mol/L, whereas the average dissociation co nstant of rabbit hyperimmune anti-LDL antibody was determined to be 2. 7x10(-8) mol/L. In conclusion, we have purified human autoantibodies r eactive with oxidized LDL that appear to be predominantly of moderate- to-low affinity and of variable cross-reactivity, The predominance of IgG1 and IgG3 antibodies is significant from the standpoint of potenti al pathogenicity, since these two subclasses activate the classic comp lement pathway system and have the highest binding affinities for Fc g amma receptors on phagocytic cells.