JOURNAL OF INTERFERON & CY'FOKINE RESEARCH 23:319-327 (2003) © Mary Ann Liebert, Inc. Differential Regulation of Cytokine Gene Expression by Avian Heterophils During Receptor-Mediated Phagocytosis of Opsonized and Nonopsonized Salmonella enteritidis MICHAEL H. KOGUT,' LISA ROTHWELL. 2 and PETE KAISER2 ABSTRACT Internalization of pathogens by phagocytic cells triggers the innate immune response, which in turn regulates the acquired response. Phagocytes express a variety of receptors that are involved in recognition of patho- gens, including (1) pattern recognition receptors (PRR), which recognize conserved motifs, (2) complement receptors (CR), which recognize complement-opsonized pathogens, and (3) Fe receptors (FcR), which recog- nize antibody-opsonized pathogens. Recognition of microbes is accompanied by the induction of multiple cell processes, including the production of proinflammatory and anti-inflammatory cytokines and chemokines. The objective of the present experiments was to use probes to known avian proinflammatory and anti-in- flammatory cytokines and 'I'aqMan technology to ascertain levels of cytokine gene expression in avian het- er()phils following receptor-mediated phagocytosis of either nonopsonized Salmonella enferitidis (SE), serum- opsonized SE, or IgG-opsonized SE. Expression of interleukin-6 (IL-6) and IL-8, considered in mammals as a proinflammatory chemokine, were upregulated following exposure to the nonopsonized or the opsonized SE. However, mRNA expression for IL-18 and interferon-'y (IFN-y) was downregulated, and the expression of mRNA for the anti-inflammatory cytokine transforming growth factor-134 ('FGF- 1 64). was upregulated. In- terestingly, IL- 1 1 3 mRNA expression was significantly upregulated in heterophils that phagocytized either the nonopsonized SE via PRRs or IgG-opsonized SE via FcRs, whereas serum-opsonized SE phagocytized by CRs induced a downregulation of IL-113 mRNA. These results suggest that signaling interactions initiated by re- ceptor recognition of the microbe surface differentially regulate the induction of inflammatory cytokines in avian heterophils. It - IJ. INTRODUCTION M 1CROI3IAL INVASION OF THE Hosr is followed by a series of events designed to control (recognition. phagocytosis, microhicidal activities) and eventually resolve (inflammation and acquired immunity) the infection.° The immediate re- .sponse to invasive pathogens, clearance via the inflammatory response, and activation of the appropriate acquired responses are all coordinated and orchestrated by the innate host de- fenses. ) Recognition of potential pathogenic microbes by the innate immune system is the function of a restricted class of cellular receptors known as the nonclonal pattern recognition receptors (PRRs), such as the toll-like receptors (TLRs). The innate sys- tem uses these germ-line encoded receptors to recognize evo- lutionarily conserved molecular motifs (pathogen-associated 'USDA-ARS, SPARC. College Station, TX 77845, Institute for Animal Health. Compton. Berkshire RG20 7N. U.K. molecular patterns {PAMP5]) of infectious microbes. 23 The phagocytic process is triggered by two distinct cell surface re- ceptors, one involving the recognition of the carhoxy-terminus of immunoglohulin (Ig) molecules by the Fe receptor (FcR) and the other where complement receptors (CR) recognize com- plement fragments .(1.5 Likewise, some PRRs, such as mannose receptors and scavenger receptors, have been shown to be in- volved in the phagocytosis process as well. 5 The end prod- uct of microbial recognition and phagocytosis by cells of the innate response is the activation of intracellular signaling path- ways that initiate cellular processes, such as activation of mi- crobicidal killing mechanisms, the production of proinfiamma- tory and anti-inflammatory cytokines. and the production of costimulatory molecules required for antigen presentation to the acquired immune system.9' ) As the first cells to migrate to a site of infection, polymor- 319