Methods for detection of immune-mediated neutropenia in horses, using antineutrophil serum of rabbit origin.

This research paper discusses the methods used for identifying immunological neutropenia (a decrease in the number of neutrophils, a type of immune cell) in horses by stimulating antineutrophil production in rabbits using highly purified equine neutrophils. Two methods, protein G-binding and indirect immunofluorescence, were found to be the most sensitive and can potentially be applied in diagnosing similar conditions in other animal species.

Research Methodology

• The researchers first produced equine neutrophil antibody in rabbits, which involved injecting the rabbits with highly purified (greater than 99.0%) equine neutrophils.
• The antibodies produced in response to the neutrophils were then detected and analyzed using a variety of techniques including agar gel diffusion, leukoagglutination (clumping of white blood cells), indirect immunofluorescence, and binding to staphylococcal protein A and streptococcal protein G.
• The antibody effectiveness was also tested through phagocytic inhibition methods, meaning the researchers observed how efficient the developed antibodies were in suppressing phagocytosis – a process where cells engulf bacteria or other foreign bodies.

Results and Interpretation

• The researchers observed precipitation lines and leukoagglutinated clusters of neutrophils in antiserum dilutions (a process to decrease concentration) of up to 1:4 and 1:64 respectively.
• The neutrophils, when treated with antiserum and exposed to fluorescein-conjugated goat anti-rabbit immunoglobulin, showed specific bright membranous fluorescence.
• The indirect immunofluorescence and the protein G-binding tests showed better sensitivity compared to the protein A-binding test. They resulted in a titer (concentration of antibodies) of 1:256, compared to the protein A-binding test’s titer of 1:32.
• Nonetheless, some nonspecific binding of protein A and protein G was observed in a small number of neutrophils. This resulted in uniform or patchy cellular fluorescence.
• Significant suppression of phagocytosis was seen when neutrophils were treated with antiserum up to a dilution of 1:8. The decrease in phagocytosis of opsonized zymosan particles was significant (P less than 0.05).

Conclusion and Implications

• From the results, the indirect immunofluorescence and protein G-binding tests proved to be highly sensitive for detecting neutrophil antibodies.
• These methods can thus be used to diagnose immune-mediated neutropenias in horses, and possibly, in other animal species as well.