Analysis of antibody to neutrophils associated with autoimmune neutropenia: Possible recognition of Fc-receptor-related molecules

The serum of a 50-year-old male with neutropenia and a bout of bacterial infection was studied. Anti-neutrophil IgG antibody was detected by indirect immunofluorescence using a laser flow cytometry system. Purified IgG from our patient's serum did not inhibit chemotaxis of neutrophils, but inhibited rosette formation of neutrophils with ox red blood cells (ORBC) coated with anti-ORBC rabbit IgG dose-dependently. Surface iodination of neutrophils followed by their immunoprecipitation by purified IgG and sodium dodecylsulfate polyacrylamide gel electrophoresis showed a single band that corresponded to 45 kilodaltons. Possibly the IgG antibody in our patient's serum recognizes molecules related to Fc receptors.