Priming by recombinant chicken interleukin-2 induces selective expression of IL-8 and IL-18 mRNA in chicken heterophils during receptor-mediated phagocytosis of opsonized and nonopsonized Salmonella enterica serovar enteritidis

Heterophils, the principal avian polymorphonuclear leukocytes (PMNs) equivalent to the mammalian neutrophil, function as professional phagocytes against bacterial infections, mediate acute inflammation, and respond to cytokine stimulation to aid in regulation of innate host defenses. Interleukin-2 (IL-2) has been found to exercise an array of biological effects on other cell types besides T lymphocytes, including NK cells, B cells, monocytes, and neutrophils. In the present experiments, using real-time quantitative RT-PCR, we evaluated the role of rChIL-2 as a priming mediator controlling heterophil responses at the level of gene transcription by examining the expression of mRNA for pro-inflammatory (IL-1beta, IL-6, IL-8) and Th1 (IL-18 and IFN-gamma) cytokine genes following stimulation with phagocytosis agonists; i.e., opsonized and nonopsonized Salmonella enteritidis. Peripheral blood heterophils were isolated and incubated with rChIL-2 from transfected COS cells. rChIL-2 selectively primed the heterophils for an increase in transcription of the pro-inflammatory cytokine IL-8 and of the Th1 cytokine IL-18 induced by all three phagocytic agonists. Although rChIL-2 priming modulated the expression of specific cytokine mRNA in heterophils stimulated by different phagocytic agonists, the rChIL-2 by itself did not directly induce gene expression of either the pro-inflammatory or Th1 cytokines. We propose that rChIL-2 could be priming heterophils solely to function as more efficient innate effector cells to limit bacterial growth through the selective increase of IL-8 and IL-18 gene expression.