IgG but not IgM anti-phospholipid antibody binding is temperature dependent

We examined the effect of temperature on the measurement of enzyme-linked immunosorbent assay (ELISA)-defined human polyclonal antiphospholipid antibody. Both IgG and IgM antibodies were easily demonstrable when sera were incubated on phospholipid-coated ELISA plates at 4-22 degrees C. When incubations were done at 37-45 degrees C IgG antibody binding markedly decreased but IgM antibody binding did not. Warming the phospholipid-coated ELISA plate alone, the serum alone, the buffer alone, or the blocking reagent alone had no effect. When the antigen content of the wells was increased fourfold the effect of warming still occurred. The effect of warmth was reversible and was seen with affinity-purified antibody as well as with whole serum. Phospholipid vesicles in suspension, however, absorbed antibody in a dose-dependent fashion at 4, 22, and 42 degrees C. These results indicate that antibody binding to phospholipid is temperature dependent when phospholipid is adherent to the solid phase. Whether the change in IgG-phospholipid interaction results from a change in antigen or in antibody remains unknown.