Isoelectric focusing of an anti-HL-A2 antiserum cross-reacting with W28.

The cytotoxic activity of an anti-HL-A2 antiserum cross-reactive with W28 appeared in three distinct peaks after the serum was subjected to isoelectric focusing. The pH at which the peaks formed was reproducible using pH 5–8 or pH 3.5–10 gradients. Anti-HL-A2 activity occurred in each peak, but the cross-reactive anti-W28 cytotoxicity appeared to be largely confined to the second and third peaks. The first peak was exclusively IgG, the second contained IgG and IgM, and the third contained IgG, IgA, and IgM.