Effects of human IL-8 isoforms on bovine neutrophil function in vitro

Interleukin 8 (IL-8) is a potent chemotactic and activating agent for human neutrophils and bovine IL-8 is chemotactic for bovine neutrophils; however, it is unclear whether IL-8 activates bovine neutrophils. Two isoforms of human recombinant (hr) IL-8 protein (77 and 72 amino acid) were used to stimulate bovine neutrophils in vitro. Bovine neutrophils exhibited significant migration in the presence of 0.1, 0.5, 1.0 and 5.0 ng ml−1 hr IL-8 when incubated for 30 min at 37°C in a modified Boyden chamber assay. Both the 77 and 72 aa forms were equally effective in inducing migration in this assay. At the highest doses of IL-8 examined (1 and 5 ng ml−1), migration was similar to migration in the presence of 20% zymosan-activated serum (ZAS) or 12 h lipopolysaccharide (LPS)-stimulated blood monocyte supernatants (CM). Significant (p<0.05) release of alkaline phosphatase (ALK-P) (from specific granules) occurred but myeloperoxidase (MPO) release and superoxide anion production were not enhanced in bovine neutrophils by either form of hrIL-8 at any of the doses tested. Significant (p<0.05) alkaline phosphatase release was observed in the presence of 10 and 100 ng ml−1 for the 72 aa form of IL-8 and only at the higher dose for the 77 aa form of IL-8. The ZAS and CM significantly enhanced neutrophil degranulation of ALK-P and MPO as well as inducing superoxide anion production. These results suggest that IL-8 may play a role in both neutrophil recruitment and activation during bovine inflammatory processes.