Ouantitation of granulocyte antibodies in sera and determination of their binding sites

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Abstract
An enzyme immunoassay using eluates was developed for the quantitation of granulocyte antibodies in sera. Incubation of donor granulocytes with sera containing granulocyte alloantibodies (NA1, NA2, NB1, 5b, HLA) or autoantibodies resulted in a significantly higher amount of immunoglobulin G (IgG) per cell than did incubation with control sera. Ultracentrifugation of the sera prior to testing reduced unspecific binding of IgG to granulocytes. In eight of 10 assessed sera from patients with Felty's syndrome eluted IgG decreased from elevated to normal levels. Ultracentrifugation further allowed determination of the binding sites of granulocyte-reactive alloantibodies. Using sera containing NA1- and NA2-specific alloantibodies 173,000-188,000 binding sites on homozygous and 84,000-110,000 on heterozygous cells were determined. A similar number was found using a Fc gamma receptor III (FcRIII)-specific monoclonal antibody. Granulocytes from patients with paroxysmal nocturnal haemoglobinuria showed greatly reduced binding sites for NA-specific alloantibodies. The binding sites for the human alloantibody NB1 ranged from 36,000 to 318,000 and for the 5b alloantibody from 44,000 to 65,000. Mean values of 139,000 binding sites for HLA antigens and 27,000 binding sites for the FcRII were determined using monoclonal antibodies.
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