Neutralization of Lewis blood group antibodies by synthetic immunoadsorbents

Production of soluble recombinant proteins with Kell, Duffy and Lutheran blood group antigen activity, and their use in screening human sera for Kell, Duffy and Lutheran antibodies

The aim of this study was to show that soluble recombinant (sr) proteins can mimic blood group antigens and be used to screen human sera for blood-group-specific antibodies. The blood of all pregnant women and pretransfusion patients should be screened for blood-group-specific antibodies to identify and monitor pregnancies at risk of haemolytic disease of the foetus and newborn (HDFN), and to prevent haemolytic transfusion reactions. Current antibody screening and identification methods use human red blood cell panels, which can complicate antibody identification if more than one antibody specificity is present. COS-7 cells were transfected to produce sr forms of the extracellular domains of the red blood cell membrane proteins that express Kell, Duffy or Lutheran blood group antigens. These sr proteins were used to screen for and identify anti-Kell, anti-Duffy or anti-Lutheran blood-group-specific allo-antibodies in human sera by haemagglutination inhibition and in solid-phase enzyme-linked immunosorbent assays (ELISAs). There is a positive correlation (correlation coefficient 0.605, P value 0.002) between antibody titre by standard indirect antiglobulin test (IAT) and signal intensity in the ELISA test. This work shows that sr proteins can mimic blood group antigens and react with human allogeneic antibodies, and that such proteins could be used to develop solid-phase, high-throughput blood group antibody screening and identification platforms.

Recombinant blood group antigens are useful for studying the fine specificity of antibodies against glycophorin A encoded antigens

Recombinant wild-type and variant forms of glycophorin A (GPA) were expressed in wild-type and glycosylation-defective Chinese hamster ovary cells. The binding to recombinant GPA of antibodies submitted to the Third International Workshop was assessed by immunoprecipitation and indirect immunofluorescence. This is a powerful approach for determining the fine specificity of antibodies to blood group antigens. The advantages and limitations of this approach are discussed.

A new, low-incidence red cell antigen (HOFM), associated with depressed C antigen

A case of mild hemolytic disease of the newborn is presented which was caused by an antibody to a hitherto unknown antigen of low incidence. This antigen, now designated as HOFM (ISBT number 700050) was detected in 6 relatives, and in all of them, it was associated with an unusually weakened expression of C antigen. The serological data indicate that HOFM may be part of the Rh system, but the genetic data, although supportive of this interpretation, are inconclusive.

The fine specificity of Lewis blood group antibodies. Evidence for maturation of the immune response

Eight human Lewis blood group antibodies were characterized for their fine specificity by the use of specific immunoadsorbents and a kinetic enzyme-linked immunosorbent assay technique. Examination of sera following immunoglobulin fractionation showed IgM anti-Le(a) exhibiting broad cross-reactivity with structures biochemically related to the Lewis antigens. IgG anti-Le(a) binding was restricted to Le(a) and Le(b) These findings are consistent with the concept of affinity maturation of the immune response, which has been previously demonstrated only in animal model systems.

Detection of anti-Lea in Le(a-b+) individuals by kinetic ELISA

Utilizing a kinetic enzyme-linked antiglobulin binding assay, eight examples of anti-Lea were detected in individuals whose Lewis phenotype is Le(a-b+). These antibodies were not detectable by routine hemagglutination techniques, but were indistinguishable from anti-Lea made by Le(a-b-) individuals in terms of their immunologic fine specificity. However, unlike most anti-Lea antibodies from Le(a-b-) individuals, none of the anti-Lea antibodies had an IgG component. Anti-Lea antibodies in Le(a-b+) individuals may represent immune responses on the continuum between autoimmunity and alloimmunity.

Specific removal of anti-red cell blood group activity from anti-HLA lymphocytotoxic sera and purification of anti-A and anti-B antibodies with lymphocytotoxic activity

Lymphocytotoxic antibodies to the red cell blood groups A and B were purified from human sera by elution from synthetic immunoadsorbents (Synsorbs from Chembiomed). The lymphocytotoxic activity of the eluted antibodies was better preserved when elution was carried out at pH 11, whereas it was less stable when elution was performed at pH3. In addition, complete removal of anti-red cell blood group activity from an anti-HLA serum was easily obtained by adsorption on the corresponding Synsorb without loss of anti-HLA activity.

Detection of IgG anti-Lewis (a) antibodies in cord sera by kinetic Elisa

Lewis blood group antibodies rarely, if ever, cause hemolytic disease of the newborn. This observation has been attributed to the absence both of Lewis antigens on fetal cells and of maternal IgG Lewis antibody. In the present study, sera from 13 mother-infant pairs were tested for the presence of anti-Lewis (a) by hemagglutination and by a sensitive and specific kinetic enzyme-linked immunosorbent assay. By routine hemagglutination methods, anti-Lea was present in all maternal samples but absent in all cord samples. By kinetic enzyme-linked immunosorbent assay, IgG anti-Lea was present in 13 of 13 maternal samples and in 12 of 13 cord samples. These results indicate that IgG anti-Lea antibodies are common and do cross the placenta. This suggests that they do not cause hemolytic disease of the newborn because of the low levels of Lewis antigens on fetal red cells.