Autoimmunity and the Kell blood groups: auto-anti-Kpb in a Kp(a+b-) patient

Kell expression on myeloid progenitor cells

Kell is one of the major human red blood cell groups and comprises 22 antigens. These antigens are produced by alleles located on chromosome 7, including sets of antithetical antigens such as Kell (K, K1) and cellano (k, K2), which differ in a single amino acid change (T193M). It consists of a 93-Kd transmembrane glycoprotein that is surface-exposed and shares sequence and structural homology with zinc endopeptidases, which are involved in regulating bioactive peptides. Anti-Kell antibodies have been shown to suppress fetal erythropoiesis. Recently published data indicate a similar effect on myeolopoiesis and megakaryopoiesis. Substantial thrombocytopenia in fetuses affected with HDN due to anti-K antibodies led to the discovery of the inhibitory effect of Kell-related antibodies on CFU-MK growth. In addition to its inhibitory effect on BFU-E growth, anti-Kell antibodies significantly reduced CFU-GM colony formation from haematologically normal individuals. Moreover, anti-cellano and anti-Kp(b) antibodies also inhibited the growth of CFU-GM from antigen positive MNC. These data indicate that Kell is not restricted to erythroid blood cells, but is expressed on a broader spectrum of haematopoietic cells than previously believed.

Autoimmune hemolysis: a critical review

Autoimmune hemolysis is defined as a shortening of erythrocyte lifespan due to antibodies directed against the individuals own red cells. This autoantibody production (by B lymphocytes) is thought to result from deficient activity of suppressor T lymphocytes. The rate of erythrocyte destruction depends on the properties of the autoantibodies and on the activities of the complement and mononuclear phagocyte systems: anemia results when destruction outweighs marrow production. Autoimmune hemolysis, which may be primary or secondary, is classified into "warm," "cold," and "mixed" types. The hemolysis associated with pregnancy. Donath-Landsteiner antibodies, of mixed type, and in children, is treated in detail. Current treatment is with immunosuppressive drugs, surgery, and plasma exchange, though immunomanipulation may become important in the future; blood transfusion may be a life-saving adjunct to other therapy.