Summary The limited supply of reagent human polyclonal antibodies to high prevalence antigens, like Jsb, is driving the search for alternative reagents. Murine immunoglobulin G (IgG) monoclonal antibodies (Mabs) and their humanized chimaeric IgM isoforms can now be used for typing patients and screening donors. Antigen typing of red blood cells (RBC) with a positive direct antiglobulin test (DAT) is also possible using these antibodies. Blood from patients with sickle cell disease and African donors were tested with reagent anti‐Jsb, murine Mab IgG anti‐Jsb [murine immunochemistry monoclonal antibody‐8 (MIMA‐8)], and humanized chimaeric IgM anti‐Jsb [human immunochemistry monoclonal antibody‐8 (HIMA‐8)] by haemagglutination and gel cards. RBC samples that were DAT positive were used to evaluate the humanized chimaeric IgM monoclonal anti‐Fya (HIMA‐19). RBC samples (n = 243) of known Jsb type were tested in parallel with MIMA‐8 and reagent anti‐Jsb, and 132 samples were tested with MIMA‐8 in gel cards and HIMA‐8 by direct tube testing. No discrepant results were obtained. DAT‐positive RBC samples (n = 27) were correctly phenotyped using HIMA‐19. We conclude that MIMA‐8 is suitable for screening donors and typing patient RBCs. Testing MIMA‐8 with gel cards containing anti‐mouse IgG enables the screening of donors by automated methods. Humanized chimaeric IgM anti‐Jsb and anti‐Fya are suitable as typing reagents by direct agglutination methods.

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