LTF and infection: Some up-regulated genes at 21 dpi (e.g., Ltf, Cxcl9, Pglyrp1, Prg2, Cxcl13, Cxcl3, Ccl9, Ccl19, Krt5, Krt14, Krt15, Krt17, and Slpi) were also identified in a previous infection study by using H1N1(PR8) [8].