Although the specificity of an antibody grows through process requiring somatic mutation, the Ag-binding polyspecificity of an antibody enlarges the Ag detection of the immune system. While the polyspecificity of antibody is its ability to bind at least two different Ags, apparent polyspecificity could also depends of characteristics of Ag considered. Whichever the type of epitopes, conformational or linear, they are commonly determined by the surface of the involved epitope residues. We demonstrate that the apparent polyspecificity of antiphospholipid antibody responsible for the antiphospholipid syndrome is due to an epitope characterized by the physical properties of amino acids whose polarity, hydropathy and steric volume but not by the sequence of residues. The physicals properties are, per se, the epitope for certain antibody. Although this novel concept provides insights on how the polyspecificity of an antibody can be linked up under the lead of a common motif of physical properties.