Defensins are a class of antimicrobial peptides in vertebrates that function as the first line of innate immunity with potent antimicrobial and immunomodulatory activities. Fourteen defensins, namely, avian β-defensin 1 to 14 (AvBD1-14), have been identified in chickens. Before characterizing the role of AvBDs in innate immunity during the early development of chickens, we collected tissue segments from the liver, spleen, and gastrointestinal (GI) tract including the esophagus, crop, proventriculus, gizzard, duodenum, jejunum, ileum, cecum, and colon from broilers at days 1, 3, 7, 14, and 28. After RNA isolation and reverse transcription, we determined the expression levels of the 14 AvBD genes in these tissues during the first 28 days after hatching by real-time PCR. The results suggested the AvBDs were widely expressed in the chicken liver, spleen, and gastrointestinal (GI) tract. Interestingly, we did not detect AvBD11 expressed in the GI tract, even in the liver and spleen. Additionally, AvBDs were differentially expressed in the chicken GI tract. AvBD5 and AvBD14 were expressed most abundantly in the proximal GI tract, especially the esophagus and crop. Moreover, AvBD5, AvBD7, AvBD9, and AvBD14 were expressed in an inverted-V pattern with the peak being the observed expression at days 3, 7, or 14 in the chicken spleen, esophagus, duodenum, and cecum. Other AvBDs presented biphasic or inverted-V expression patterns in different tissues. The expression levels of all detected AvBDs were strengthened after hatching rather than decreasing steadily. Therefore, AvBDs were found to be expressed widely in the chicken liver, spleen, and GI tract and their expression levels were primarily up regulated during the early development of chicken, implying the potential essential roles of AvBDs in early innate defense and infection resistance of chickens.
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