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Human red cells incubated with a solution containing 6% 2-aminoethylisothiouronium bromide (AET) lose activity of antigens that are part of, or related to, the Kell blood group system. However, Kx antigen is not inactivated. Studies on a wide range of other blood-group antigens show no other evidence of changes and AET appears to react specifically with red-cell membrane structures that have Kell activity. The AET procedure produces an artificial K0 red cell that can be used in blood group serology, and allows easy recognition of antibodies that are associated with the Kell system. AET has been used by other workers to produce a red cell that has many serological and biochemical characteristics of a PNH cell. Our studies on red cells from PNH patients have not shown any changes in Kell blood-group antigens.

A 19-year-old patient with a long history of idiopathic thrombocytopenic purpura developed a potent antibody against a high-incidence antigen in the Kell blood group system. The direct antiglobulin test on his red cells was negative. His cells exhibited profound depression of Kell blood group antigens, but antigens of other blood groups were normal. Transfusion of incompatible blood was well tolerated and differential agglutination tests, using selected Rh antisera, showed in vivo survival of the transfused red cells for more than 8 weeks. However, the transfused red cells also showed acquired loss of Kell antigens. Five months after the initial findings, Kell-related antibody disappeared and Kell antigens reappeared on his red cells. The patient's serum stored from the initial investigation now reacted with his freshly collected red cells. These data suggest that an environmental agent in the patient's plasma was responsible for the temporary loss of Kell antigens from red cells in his circulation.

Red cells of the McLeod blood group phenotype have weak Kell antigens, lack Kx antigen and have acanthocytic morphology. We have immunoprecipitated Kell antigens from McLeod red cells and show that they are markers on the same 93 kDa membrane protein that carries Kell antigens on normal red cells. However, as determined by Western immunoblotting, McLeod red cells have a marked deficiency of this protein. We have also studied the near-neighbour relationship of McLeod and common Kell red-cell membrane proteins by cross-linking intrinsic sulphydryl groups by oxidation, catalysed with orthophenanthroline and copper, or by cross-linking amino groups with dimethyl-3,3'-dithiobispropionimidate. Results were analysed by diagonal mapping in two-dimensional gels. No abnormalities of membrane protein inter-relationship were detected in McLeod red cells. We have isolated Kx antigen from K0 red cells by immunoprecipitation with human alloimmune anti-Kx serum, isolation of immune complexes from detergent-solubilized cell membranes with protein A-Sepharose and analysis of the eluted immune complex by SDS-PAGE under reducing conditions. Kx antigen is a marker on a red-cell membrane protein of approximately 37 kDa. Ko (Knull) red cells have about twice the amount of Kx antigen as do red cells of common Kell type. McLeod red cells have no detectable Kx antigen by serological tests or by immunoprecipitation.

Fifteen antigenic determinants are known to be related to the Kell blood group. Some boys with X-linked chronic granulomatous disease have the very rare McLeod or Ko phenotype on their red cells. Serological studies of the McLeod type suggest that the weak Kell antigens that are present differ qualitatively and quantitatively from those on red cells of common Kell type. A new antigen, Kx, has been characterized and shown to be present on red cells and neutrophil leucocytes. Lack of red-cell Kx is associated with the McLeod phenotype, lack of leucocyte Kx is associated with chronic granulomatous disease.

The McLeod phenotype is inherited as an X-linked characteristic. The red cells have weak antigenicity in the Kell blood group and lack Kx, a precursor-like substance that appears to be necessary for proper biosynthesis of Kell antigens. Kx antigen is also required for establishment of normal cell morphology. Absence of Kx antigen causes a membrane abnormality, in which the most prominent feature is acanthocytosis, and a compensated haemolytic state. The X-linked gene that determines normal Kx production is called X1k. Inheritance of a variant allele at the Xk locus is responsible for lack of Kx synthesis and the McLeod phenotype. The Xk locus is inactivated by the Lyon effect, and female carriers of the variant gene exhibit blood group mosaicism in the Kell system and have a dual red cell population of acanthocytes and discocytes.

Some boys with X-linked chronic granulomatous disease (CGD) have red cells of the rare McLeod phenotype in the Kell blood group system. Only one example of this phenotype has previously been described in a non-CGD subject. We have studied a 10-year-old boy and a maternal brother who do not have CGD and whose red cells are of the McLeod type . The boy presented as a haematological problem with red-cell abnormalities. These were acanthocytosis, anisocytosis and 'tailing' in the osmotic fragility curve, changes now known to occur with the McLeod phenotype. Subsequent studies revealed his rare blood group. A family study has established that an uncle also has acanthocytic red cells and the McLeod phenotype. In addition the boy's sister, mother and maternal grandmother all show red-cell mosaicism with double populations of McLeod acanthocytes and normal red cells of common Kell type. The gene that determines inheritance of the McLeod phenotype is X-linked and the mosaicism present in female carriers is believed to result from X chromosome inactivation by the Lyon effect. The study provides further evidence that the McLeod phenotype arises by inheritance of a variant X-linked modifying gene and not through inheritance of a variant gene at the Kell autosomal locus. It also represents the first occasion that a person of rare blood group has been recognized because of an associated anomaly in red cell morphology.

Congenital dysgranulopietic neutropenia (CDN) is a recently proposed entity that describes a small subgroup of children with clinically severe neutropenia. We followed and studied a 3-year-old girl with neutropenia (less than 500/mm3) and recurrent severe infections in whom repeated marrow evaluations revealed large (30-50 microns) multinucleated promyelocytes to polymorphonuclear cells with as many as 4 to 16 nuclei or nuclear lobes, respectively. In addition to the nuclear endoreduplication, ultrastructural and cytochemical evaluation of these cells demonstrated abnormalities in granule genesis and centriole structure. Concomitantly, immunoperoxidase staining indicated that many of the granules were devoid of lactoferrin but not lysozyme. In vitro proliferation studies revealed normal to increased thymidine labeling, normal numbers of colony-forming cells, and normal colony-stimulating activity from blood and marrow mononuclear cells, findings consistent with ineffective myelopoiesis. However, serum folate, B12, and lysozyme levels were normal. The nuclear and cytoplasmic abnormalities in this patient result in an extreme example of CDN, distinct from previously described cases.

Approximately one in 250 people with autoimmunity involving their red cells have IgG autoantibodies with specificity in the Kell blood groups. Red cells of these individuals have an acquired temporary weakening of their Kell antigens. Some of the patients also have allo-anti-K in their serum. This report presents a case in which an IgG autoantibody may define a new high-incidence red cell antigen related to the Kell blood groups. The patient's Kell blood group antigens are depressed, and his serum contains allo-anti-K. It is postulated that reduced red cell Kell antigenicity is caused by enzymatic degradation, possibly of bacterial origin, and that the acquired loss of Kell antigens, the Kell-specific autoimmune state, and the serum all0-anti-K, are all related aspects of one phenomenon.