Three novel Anas platyrhynchos avian β-defensins, upregulated by duck hepatitis virus, with antibacterial and antiviral activities.

Three novel Anas platyrhynchos avian β-defensins (Apl_AvBDs), Apl_AvBD4, 7 and 12, were identified successfully and characterized in tissues from Peking ducks in the present study. The cDNA fragment of Apl_AvBD4 contained 171 bp, and encoded 56 amino acids. The complete nucleotide sequences of Apl_AvBD7 and 12 contained 204 bp and 198 bp open reading frames, which encoded 67 and 65 amino acids, respectively. Both recombinant and synthetic forms of the three Apl_AvBDs showed antibacterial activity against most of the bacteria investigated, including Gram-negative and Gram-positive bacteria, except for Salmonella choleraesuis. In addition, the antibacterial activity of all the three Apl_AvBDs decreased significantly in 150 mM NaCl. Significant antiviral activity of the three Apl_AvBDs was shown against duck hepatitis virus (DHV). However, none of the Apl_AvBDs showed significant hemolytic activity. Additionally, the expressions of the three Apl_AvBDs in response to DHV infection was highly variable, and significant upregulation of Apl_AvBD7 in liver was found in response to infection at different time points. Expression of Apl_AvBD4 in thymus, and of Apl_AvBD7 in bone marrow was induced in a time-dependent fashion by DHV infection. In contrast, expression of Apl_AvBD12 was found to be significantly decreased, and was hard to detect in cecal tonsil, spleen, bursa of Fabricius, and thymus of ducks at some time points after DHV infection. The present results demonstrate that Apl_AvBDs play vital roles in the immune response of ducks against bacterial and viral pathogens.