Normal human IgG with antibody activity for keyhole limpet haemocyanin.

Consistent 7S (9/9 sera tested) and occasional 19S (1/9 sera) KLH-binding activity was detected in sucrose gradient fractions of normal rabbit sera. Similar 7S activity was detected in pooled HGG. By affinity chromatography on a KLH-Sepharose immunoadsorbent, a fraction of HGG was obtained, representing 0.04–0.2 per cent of the starting material, which was enriched in KLH-binding activity as detected by four primary antigen-binding methods, but not by immunodiffusion, complement fixation or passive haemagglutination. The active material was electrophoretically heterogeneous, and contained only γ heavy chains and both κ and λ light chains. By inhibition RIA, 63 μg of natural human IgG anti-KLH gave equivalent binding to that observed with 1 μg of hyperimmune rabbit IgG anti-KLH. KLH-binding activity was demonstrable in twelve of eighteen individual human sera tested.