CASP3 and autoimmune polyendocrinopathy: Studies using domain deletion mutants of β2GPI, in which one or more domains are missing, have shown that the immunodominant epitope which binds the pathogenic anti-β2GPI APS autoantibodies is located in DI5, 6 and recombinant DI can bind these APS autoantibodies in both the solid and fluid phase.31, 32 Pre-incubating APS-positive IgG from individual patients with recombinant human DI, prior to treatment of cells, reduced cleaved caspase-3 in H/R injury (Figure 5b).