Autoimmune neutropenia in infancy due to anti-NA1 antibody: detection of antibody with immunofluorescence and agglutination test.

The sera from two patients with chronic neutropenia in infancy were examined for the presence of antineutrophil antibodies and their specificity against neutrophil antigen by using granulocyte indirect immunofluorescence test and microleukocyte agglutination test. In the microleukocyte agglutination test, the patients' sera reacted with neutrophils from their parents and normal unrelated donors having the neutrophil antigen NA1, but not with neutrophils from NA1- donors. After the absorption of patients' sera with NA1+ neutrophils, the antibody activity was completely abolished, resulting in the confirmation of the anti-NA1 antibody. In contrast, the granulocyte indirect immunofluorescence test showed positive reactions against both NA1+ and NA1- neutrophils, and the specificity for anti-NA1 was found in the results of the sera absorbed with NA1+ neutrophils. This suggested that the absorption experiment might be necessary to determine the specificity of the antibody for neutrophil antigen. Thus, we confirmed two cases with autoimmune neutropenia caused by anti-NA1 antibody. A combination of agglutination and immunofluorescence techniques would be recommended for investigation of neutrophil antibodies against the neutrophil-specific antigen.