Abstract. Heterophil function was eva luated in 16 healthy chickens and in 46 chickens with experime ntally
induced sta phylococcal tenosynovitis. In paired blood samples, heterophils from chickens with tenosynovit is
had a significant increase in adherence, chemo tax is, phagocytosis, and bact erial killin g of Staphylococcus aureus
compared to heterophils from healthy chickens. Th e percent adh erence of heterophils to nylon fiber columns
increased significantly from a 78.4% mean ± 6.6% standa rd deviation to 87.6% ± 3.2% after induction of
sta phylococcal tenosynovitis. Heteroph il movement following in vitro expos ure to saline or endo toxi n was
increased in chickens with tenosy novitis; 3 ± I heterophils/0.25 rnrn- to 10 ± 6 heterophils/0.25 mrn ? and 136
± 29 heterophils/0. 25 mrn - to 340 ± 74 het erophils/0.25 mm -, respe ctively. Endotoxin-acti vated seru m was
chemoatt ractive for heterophils from all chickens. Flow cyto metry was used to define the heterophil population
on light scatte r histogram s, eva luate ind ividual cell phagocytosis of latex bead s, and quantitate the number of
bead s phagocytosed per heterophil. When incubated with increased num bers of beads, only heterophils from
chickens with tenosynovitis phagocytosed higher numbers of beads . At heterophil to bead rat ios of I : 10, the
percent age of heterophils that pha gocytosed bead s increased from baseline values of 37.8% ± 9.0% to postinfection
values of67.3% ± 7.5%. Using I : 20 heteroph il to bean rati os, heterophil phago cytosis increased from
38.7% ± 9.9% to post-infection values of79.8% ± 7.3%. Heterophils from all chickens were able to phagocytose
and kill log phase sta phylococca l bacteria. After phagocytosis, the heterophils from chicke ns with staphylococcal
tenosyn oviti s rapidl y decrea sed the number of viable bacterial colony forming-units per millil iter by approximately
one log. Circulating heterophils from chickens with experime ntally induced staphylococcal tenosynoviti s
therefore appear to have increased functional capabilities in this bacterial inflam matory disease.