Lutheran

The Lutheran blood group system consists of 19 antigens: four pairs of antithetical antigens—Lu^a /Lu^b, Lu6/Lu9, Lu8/Lu14, and Au^a /Au^b —and 11 antigens of very high frequency. These antigens are located on four of the five immunoglobulin-like domains of both isoforms of the Lutheran glycoprotein. The LU gene is on chromosome 19 and comprises 15 exons. The two glycoprotein isoforms differ in the length of their cytoplasmic tails as a result of alternative splicing of intron 13. Lu_nullphenotype arises from homozygosity for inactivating mutations in the LU gene. The dominantly inherited Lu_modphenotype, In(Lu), results from heterozygosity for inactivating mutations in KLF1, the gene for the erythroid transcription binding factor EKLF. Clinically, antibodies of the Lutheran system are relatively benign. When hemolytic, they generally cause only mild, delayed hemolytic transfusion reactions or hemolytic disease of the fetus and newborn that can be treated by phototherapy. The Lutheran glycoproteins, which are members of the immunoglobulin superfamily of adhesion molecules and receptors, bind isoforms of laminin with α5 chains, components of the extracellular matrix abundant in vascular endothelia. The primary function of the Lutheran glycoproteins on RBCs could involve the transfer of maturing RBCs from the bone marrow to the peripheral circulation. They could also be involved in vascular occlusion and thrombotic events as complications of sickle cell disease and polycythemia vera, respectively. Immunohematology2009;25:152–159.