Evidence that the granulocyte-specific antigen NC1 is identical with NA2

The neutrophil-specific antigen NC1 is defined by an antibody in the serum of a mother who gave birth to a child with alloimmune neonatal neutropenia. NC1 has been reported to be associated with the neutrophil-specific antigen NA2, but the precise relation of NC1 and NA2 remained unclear. Therefore, we investigated the serum using the antigen capture assay MAIGA and the granulocyte (GIFT) and lymphocyte (LIFT) immunofluorescence tests. In GIFT, no NA association was observed. In LIFT, serum antibodies bound preferably to lymphocytes with the HLA antigens HLA-B7 and cross-reacting antigens. In MAIGA, an antibody specific for the NA2 variant of the granulocyte Fc gamma-receptor III was observed. The NA2 specificity was confirmed by testing granulocytes from 40 further different donors. This indicates that the NC1 and NA2 antigens are identical. A positive GIFT result but a negative one in LIFT using cells of an NA2-negative typed individual suggest the presence of an additional, non-NA2-specific granulocyte antibody.