An indirect flow cytometric test for detection of anti-neutrophil antibodies in dogs

Abstract

To develop a clinically applicable assay for detection of serum anti-neutrophil antibodies in dogs. Serum samples of 20 healthy dogs and 20 sick dogs. An indirect immunofluorescence assay was developed in which canine serum was incubated with paraformaldehyde-fixed neutrophils and subsequently incubated with fluorescein-conjugated rabbit anti-dog IgG. Neutrophil median fluorescence intensity and the percentage of neutrophils with an increase in fluorescence intensity were determined by use of a flow cytometer. Neutrophils incubated with serum from healthy and sick dogs had a normally distributed curve when displayed as a histogram. Alloantibodies or immune complexes that significantly affected test results were not detected. Hyperglobulinemia did not appear to affect test results. The neutrophil donor did not significantly affect test results. With 1 exception, results for the sick dogs did not differ appreciably from those for healthy dogs. Serum from a dog with steroid-responsive neutropenia had a greater neutrophil fluorescence value and percentage of neutrophils with an increase in fluorescence intensity, compared with either healthy or sick dogs. The indirect immunofluorescence test gave consistent results for healthy and sick dogs and detected anti-neutrophil antibodies in a dog with steroid-responsive neutropenia. Definitive evaluation of the test will be dependent on evaluation of persistently neutropenic dogs and correlation of test results with a response to immunosuppressive therapy.