Measurement of avidity of serum autoantibodies to Aβs and its significance in patients with Alzheimer's disease

Abstract

Objective To measure the avidity of serum autoantibodies to Aβs in patients with Alzheimer's disease (AD). Methods Enzyme-linked immtmoserbent assay (ELISA) combined with thiocyanate elution technique was employed to detect the avidity of serum autoantibodies to Aβs in patients with AD, middle-aged and healthy elderly adults (n=20). Results The avidity of serum autoantibodies to Aβs in patients with AD (avidity index, 1.6 [1.15 to 2.05]) was significantly lower as compared with that in healthy elderly subjects (avidity index, 2.45 [1.75 to 3.08]) (P=0.020) and no significant difference was showed in the avidity of autoantibodies to Aβs between the elderly and middle-aged healthy adults (P=0.221). An evident shift to the low section was observed in patients with AD in the avidity distribution histogram. The proportion of low affinity antibodies was significantly higher in patients with AD (13% [5% to 18%]) than that in healthy elderly subjects (5% [3% to 10%]) (P =0.000), and the proportion of high affinity antibodies was significantly lower in patients with AD (15% [5% to 24%]) than that in elderly adults (35% [26% to 44%]) (P=0.006). Conclusion Low avidity of autoantibodies to Aβs is confirmed in AD patients. Patients with AD show a significantly high proportion of low affinity antibodies than normal adults and the components of polyclonal antibodies change in patients with AD, probably resulting from incomplete immune tolerance of B cells. Key words: Alzheimer's disease; Autoantibodies to Aβs; Avidity