[The HLA system and habitual abortion]

HLA-antigens are extremely polymorphic. A calculation of the polymorphism shows a number of 398.476.343 possible HLA-phenotypes, if HLA-A, -B, -C and -DR antigens are taken into account. The compatibility of HLA-antigens of recipient and donor plays a crucial role in transplantation: HLA-antigens are the traits, which are recognized by the immune system of the recipient in the frame of a rejection of the transplant or by the donor in the frame of a graft-versus-host reaction. Large international statistics show that HLA-incompatibility between recipient and donor leads to short transplant function periods, while compatibility brings about good transplant function. Therefore, matching of HLA-antigens plays an important role in transplantation of solid organs, mainly kidneys (3, 4, 5), and is completely necessary in bone marrow transplantation. Also in pregnancy, HLA-antigens are important: If HLA compatibility between mother and child is high, the risk for habitual abortion is higher than in normal pregnancies (6, 7).