Fluorescein isothiocyanate staining and characterization of avian heterophils

Fluorescein isothiocyanate (FITC) was found to stain cytoplasmic granules of avian heterophilgranulocytes. In tissue sections, the fluorescent granulocytes were predominantly distributed adjacent to trabecular bones. The fluorescein stained granulocytes were abundant in synovial fluids of chickens with synovitis. A significant correlation was observed in the percent of fluorescein labeled granulocytes in blood smears and the percent of heterophils determined using an automated counting method, in unstained blood from normal and Escherichia coli-infected turkeys. The fluorescein-binding heterophils purified from chickens showed a time dependent increases in the oxidation of 2',7'-dichlorofluorescin diacetate (DCF-DA) and the reduction of nitroblue tetrazolium (NBT) which were indicative of changes in oxidative burst in response to phorbol 12-myristate 13-acetate (PMA), Salmonella typhimurium lipopolysaccharide (LPS), and zymosan A (ZA). These heterophil-activating agents, also, caused significant degranulation at 16 h post-treatment, as indicated by the loss fluorescence. There were microscopically visible alterations in the cell shapes and a decrease in the density of granules due to treatment with LPS, PMA or ZA. In addition, these cells also showed phagocytic response which was evident at 30 min of incubation with fluorescent latex particles. Both chicken and turkey heterophils produced interleukin-6 in vitro at 24 h in response to LPS but not to PMA, FMLP or ZA. The chicken heterophils showed spontaneous production of matrix metalloproteinases (MMP) which was significantly enhanced by treatment with LPS, PMA, and ZA; however, LPS appeared to be most effective in inducing MMP production. These results demonstrate that the functions of heterophils can be differentially regulated by different activating agents and the fluorescein binding property of these cells may be useful for their histochemical identification.