Abstract: A monoclonal chimeric immunoglobulin wherein the heavy chains and the light chains are human by nature in their constant parts, in particular, the heavy chain constant parts are chosen from the group formed of the heavy chain constant parts of an IgA, of an IgG or of an IgM and the light chain constant parts are chosen from the group formed of the kappa chains and the lambda chains, and the light chain and the heavy chain variable parts are chosen from the group formed of monoclonal antibodies specific to monomorphic epitopes of HLA class I antigens and monoclonal antibodies specific to monomorphic epitopes of HLA class II antigens. A process for standardization of the screening and for quantification of anti-HLA antibodies in a liquid medium is also described.