Evaluation of Antineutrophil IgG Antibodies in Persistently Neutropenic Dogs

Abstract

Background:Immune‐mediated neutropenia (IMN) is one of several causes of persistent neutropenia in dogs. A test to detect IMN in dogs is not available.Hypothesis:A flow cytometric immunofluorescence assay will provide a sensitive method for detection of antineutrophil antibodies in dogs.Animals:The study included 12 neutropenic dogs and 20 healthy dogs.Methods:An indirect immunofluorescence assay was used to detect immunoglobulin G (IgG) binding to dog neutrophils. Leukoagglutination was evaluated by light microscopy. Neutrophil distribution in scatter plots, neutrophil fluorescence intensity, and the percentage of neutrophils with increased fluorescence intensity was evaluated by use of flow cytometry.Results:Antineutrophil antibodies were detected in the serum of 5 of 6 dogs with a clinical diagnosis of IMN. Leukoagglutination was present in 3 dogs. Four dogs had altered neutrophil distribution in forward‐angle versus side‐angle light scatter plots. Five of 6 dogs had increased neutrophil fluorescence intensity and 4 of 6 dogs had an increased percentage of neutrophils with increased fluorescence intensity.Conclusions and Clinical Importance: The flow cytometric test for antineutrophil antibodies detects dogs with a clinical diagnosis of IMN. Testing for antineutrophil antibodies should include observation for leukoagglutination, observation of scatter plots for altered distribution of the neutrophil population, observation of the shape of the fluorescence histogram, determination of neutrophil fluorescence intensity, and determination of the percentage of neutrophils with increased fluorescence intensity.