Gene expression profiling of avian macrophage activation

Through the process of phagocytosis, the macrophage is responsible for the clearance and destruction of both intracellular and extracellular pathogens. When stimulated, macrophages undergo a process of activation involving an increase in size and motility, enhanced phagocytic, bactericidal, and tumoricidal activity, and up-regulation of several cell-surface markers. One well characterized method of mammalian macrophage activation involves the Toll-like receptor (TLR) pathway. TLRs are surface molecules that function as direct receptors for microbial components. Binding of ligand to TLRs results in activation of transcription factors that regulate genes involved in microbial killing, apoptosis, and antigen recognition, as well as pro- and anti-inflammatory cytokines and chemokines. We have constructed a 4906-element (14,718 spot) avian macrophage-specific cDNA microarray (AMM). The AMM contains 16 of the approximately 44 genes identified within the mammalian TLR pathway. This array was used to examine the transcriptional response of avian macrophages to Gram-negative bacteria and their cell wall components and to evaluate the contribution of the avian TLR pathway to that response. Of the elements on the AMM, 981 (20%) exhibited significant (greater than two-fold, p < 0.01) changes in expression during phagocytosis of Escherichia coli and 243 (5%) exhibited significant expression changes during exposure to lipopolysaccharide (LPS). A unique set of overlapping elements (154), were observed to exhibit significant changes in expression for both phagocytosis and LPS stimulation, representing a set of core response elements. Of these elements, 63% were commonly induced, while 32% were commonly repressed. Both LPS and bacteria were found to induce NFκβ and several end products of the TLR pathway.