Characterizing Responses to Heat Stress and Immune Stimulation Using Transcriptomics in Chicken Immune Tissues

Heat stress negatively impacts poultry health and performance, including growth rate, egg production, and disease resistance. Although decreased circulating antibody levels, increased pathogen shedding, and other immunosuppressive effects of heat stress have been characterized in chickens, the mechanisms underlying these reduced immune responses need to be better understood to improve poultry heat tolerance and immune capabilities. RNA-sequencing (RNA-seq) was used to provide a transcriptome-wide measure of the effects of exposure to high temperatures in three chicken immune tissues (spleen, bursa and thymus) from two genetic lines (a heat tolerant inbred Fayoumi line and a heat-susceptible outbred broiler line). At 22-days-old, chickens were exposed to acute heat stress and/or lipopolysaccharide (LPS) in four treatments (Thermoneutral + Saline, Thermoneutral + LPS, Heat + Saline, and Heat + LPS). Responses to bacterial LPS were included to model endotoxemia and investigate heat stress interactions with a pro-inflammatory stimulus. Indexed cDNA libraries from individual tissue samples (n = 3-4 libraries/tissue/treatment/line) were sequenced using the Illumina HiSeq 2500. Differential expression analyses identified 1,300-2,500 significant genes in each tissue, with greater responses in spleen and bursa in Fayoumi, and in thymus in broiler. Pathway analyses further revealed distinct responses in each tissue and each genetic line. Expression changes in cell adhesion, cell signaling, and immune pathways provide insight into the effects of heat stress on immune tissues and targets to improve heat tolerance and disease resistance in chickens. USDA-NIFA-AFRI Climate Change Award #2011-67003-30228; the USDA National Institute of Food and Agriculture, Hatch project #5358.