PTPRC and systemic lupus erythematosus: Indeed, we initially demonstrated using enzymatic manipulation and immunoprecipitation that the canonical HP-dependent autoreactivity of lupus IgG 9G4 autoantibodies is directed against N-acetyl-lactosamine (NAL) glycans expressed by the I/i blood group antigens and other multiple mammalian glycoproteins including B220, thereby accounting for the BCB activity of these autoantibodies [16].