Platelet aggregation by hepatitis B surface antigen-antibody complexes.

Platelet aggregation indicating antigen-antibody complex formation was observed when hepatitis B surface (HBs) antigen and antibody were mixed. Platelet aggregation titers were determined for serum specimens found positive by radioimmunoassay for either HBs antigen or HBs antibody. From these determinations, incidence of HBs antigen-antibody complexes was found to be higher in HBs antigen seraas than in HBs antibody sera. There was an inverse correlation between platelet aggregation titers and radioimmunoassay values that was statistically significant for HBs antigen sera but not for HBs antibody sera. The incidence of anti-complementary activity was twice as high for platelet aggregation-positive HBs antigen and antibody sera as for platelet aggregation-negative sera. HBs antigen sera that were positive by platelet aggregation exhibited nearly three times the incidence of anti-complementary activity as did HBs antibody sera. However, the low incidence of anti-complementary activity was distributed about equally between HBs antigen and antibody sera that were negative by platelet aggregation. Additional HBs antigen preincubated with HBs antigen-positive sera effectively inhibited platelet aggregation, whereas additional HBs antibody was somewhat less effective. On the other hand, preincubation of HBs antigen sera with anti-IgG serum effectively enhanced platelet aggregation, whereas preincubation of HBs antigen sera with HBs antibody did not.