[Demonstration of antineutrophil antibodies using radioiodinated protein A]

The granulocyte associated IgG in normal and neutropenic subjects has been determined by a direct quantitative assay using radiolabeled staphylococcal protein A. This assay allows us to postulate an immunological mechanism to explain the neutropenia in 19 cases of neutropenias associated with malfunctions of the immune system and in 4 cases of idiopathic neutropenias. Discussed in this report is the possible interaction of immune complexes bound in vivo to the granulocytes. By an immunofluorescence test, it has been possible to detect IgG or IgM antibodies in only 52% of patients with a positive direct assay. The determination of granulocyte-associated IgG is therefore a better indicator in our study for defining an auto-immune neutropenia than the detection of free antibodies in the sera.