Widespread extrahepatic expression of acute-phase proteins in healthy chicken (Gallus gallus) tissues

Acute phase proteins (APP) are plasma proteins that can modify their expression in response to inflammation caused by tissue injury, infections, immunological disorders or stress. Although APP are produced mainly in liver, extrahepatic production has also been described. As a prerequisite to get insight the expression of APP in chicken during diseases, this study investigated the presence of five APP, including alphal-acid glycoprotein (AGP), Serum Amyloid A (SAA), PIT54, C-Reactive protein (CRP) and Ovotransferrin (OVT) in twenty tissues collected from healthy chicken (Gallus gallus) by quantitative Real Time PCR and immunohistochemistry. As expected, APP gene abundance was higher in liver compared with other tissues. The mRNA coding for CRP, OVT and SAA was detected in all analyzed tissues with a higher expression in gastrointestinal tract, respiratory and lymphatic samples. SAA expression was particularly high in cecal tonsil, lung, spleen and Meckel's diverticulum, whereas OVT in lung, bursa of Fabricius and pancreas. AGP and PIT54 mRNA expression were detected in all tissues but at negligible levels. Immunohistochemical expression of AGP and OVT was variably detected in different organs, being identified in endothelium of every tissue. Positive cells were present in the epithelium of the mucosal layer of gastrointestinal tract and kidney. Lung and central nervous system stained for both proteins. No positive staining was detected in lymphoid tissues and muscle. These results suggest that most tissues can express different amount of APP even in healthy conditions and are therefore capable to mount a local acute phase reaction.