Global changes in gene expression by human polymorphonuclear leukocytes during receptor-mediated phagocytosis: Cell fate is regulated at the level of gene expression

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Abstract
Phagocytes are a critical component of the innate immune response in humans and eliminate invading microorganisms through a process known as phagocytosis. Two distinct receptor-linked phagocytic pathways, one with Ab receptors (FcRs; FcR, Fc receptor) and the other complement receptors (CRs), mediate binding and ingestion of pathogens by human polymorphonuclear leukocytes (PMNs). Although progress has been made toward defining complex signal transduction processes that underlie phagocytosis in each pathway, very little is known about gene regulation during or after phagocytosis. Therefore, we used human oligonucleotide microarrays to identify changes in expression of 12,561 genes accompanying FcR- and CR-mediated phagocytosis. Eighty-four percent of 279 differentially expressed genes were induced or repressed 90 min after ingestion of Ab- and/or complement-opsonized particles. Unexpectedly, more than 30 of these genes encoded proteins involved in at least three distinct apoptotic pathways. Ninety-four differentially expressed cell fate-related genes were identified between 180 and 360 min after phagocytosis and most were induced or repressed by PMNs activated through both receptors simultaneously. By using flow cytometry, we found that FcR- and CR-mediated phagocytosis each promoted programmed cell death in human PMNs; however, phagocytosis mediated by the combination of FcRs and CRs induced apoptosis earlier than that by either receptor alone. Our results reveal distinct patterns of receptor-mediated gene expression that define complex inducible apoptotic pathways in activated PMNs. Most significantly, we discovered that programmed cell death is regulated at the level of gene expression. Thus, we hypothesize that gene regulation in PMNs facilitates resolution of inflammatory responses.