There have been no reports of severe haemolytic disease of the newborn (HDN) due to Gerbich (Ge) antibodies. Two babies with HDN due to anti-Ge3, both born to the same mother, are described. The anti-Ge appeared in the first pregnancy and was not detectable in the first trimester, the babies' reticulocyte and bilirubin values were not greatly elevated (similar to HDN due to Kell antibodies), and the anaemia in both cases was either not apparent or not severe until 2 to 4 weeks after birth. Ge antigens are found on glycophorins (GPs) C and D; GPC, like Kell, has been shown to be expressed early on erythroid progenitor cells. The maternal anti-Ge3 was shown to promote phagocytosis of Ge+ early erythroid progenitors by monocytes (similar to what has been reported with anti-K and K+ progenitor cells). Thus, anti-Ge3 may cause immune destruction of erythroid progenitors and possibly suppression of erythropoiesis (which would explain the reticulocyte and bilirubin values seen in both cases). Anti-Ge3 appears to be capable of causing severe HDN. We suggest that babies born to mothers with anti-Ge should have their haemoglobin concentrations monitored for signs of anaemia for several weeks after birth. Functional assays may prove useful.

The monoclonal antibody-specific immobilization of erythrocyte antigens (MAIEA) technique is an immunoassay devised primarily for locating blood group antigens on specific red-cell membrane proteins. The assay involves the incubation of intact red cells with two antibodies, one human alloantibody, the other a nonhuman antibody, usually a rodent monoclonal antibody, but polyclonal antibodies of rabbit origin have been utilized. For a positive result, both antibodies must bind to the same membrane protein. The red cells are lysed, the membrane solubilized and the trimolecular complex of two antibodies and membrane protein is captured in a well coated with goat antirodent (or rabbit) immunoglobulin. The immobilized complex is then detected by the use of peroxidase-conjugated goat antihuman (or rodent) immunoglobulin. Negative results, due to mutual blocking between the human and animal antibodies when their epitopes are close together on the same molecule, have permitted a degree of localization of epitopes on some proteins. This has been most effective in the mapping of Cromer blood group system antigens on the complement control protein domains of decay-accelerating factor (DAF, CD55), but has also proved informative in the clustering of antigens on the Lutheran and Kell glycoproteins. MAIEA is an effective tool for the identification of antibodies to Knops-system antigens on complement receptor 1 (CR1, CD35) in immunohaematology reference laboratories. These antibodies are clinically unimportant, but must be identified before they can be ignored for transfusion purposes.

A distinction between CDAII and HS can be made using the EMA Binding test and anti-CD44 binding. Confirmation of CDAII can subsequently be made based on clinical presentation together with either bone marrow examination or DNA sequencing of SEC23B. © 2016 International Clinical Cytometry Society.

Kna, McCa, Sla and Yka are red cell antigens of relatively high frequency, located on complement receptor 1 (CR1, CD35). Antibodies to these Knops system antigens are not uncommon. They are not haemolytic and do not reduce the survival of transfused incompatible red cells, but they are a nuisance in transfusion laboratories as they can cause an incompatible crossmatch and must be identified before they can be dismissed as clinically insignificant. Human red cell alloantibodies can be shown to be Knops system antibodies by the monoclonal-antibody-specific immobilization of erythrocyte antigens (MAIEA) test, using murine monoclonal anti-CR1. In addition to confirming that Kna, McCa, Sla and Yka are located on CR1, the MAIEA test was used to confirm that Csa is not on CR1. Red cells of the Helgeson phenotype, the null phenotype of the Knops system by conventional serological methods, have levels of Kna, McCa, Sla and Yka intermediate between those of alpha-chymotrypsin-treated cells (which lack Knops system antigens) and those of positive control cells. Level of expression of Knops system antigens is very variable and intensity of staining of immunoblots probed with monoclonal anti-CR1 correlated with strength of Knops system antigens, as determined by the MAIEA test. In individuals heterozygous for alleles producing different allotypes, separate bands representing each allotype on an immunoblot showed identical intensity of staining, suggesting that the quantity of CR1 on red cells is controlled, at least in part, by a locus independent of CR1. An analysis of CR1 on red cells of individuals who have made Knops system antibodies suggested that the Knops system antigens and the antibodies that detect them are complex and heterogeneous.