Expression of duck CCL19 and CCL21 and CCR7 receptor in lymphoid and influenza-infected tissues

Ducks are the natural host and reservoir of influenza viruses. We are interested in their immune responses to these viruses, to understand host-pathogen interactions and to develop effective agricultural vaccines. We identified duck homologues of the chemokines CCL19 and CCL21 and cloned their cognate receptor, CCR7. Conservation of key features, and expression in lymphoid tissues suggests that these chemokines are the direct orthologues of their mammalian counterparts. Mammalian CCL19 and CCL21 are responsible for the homing of dendritic cells and naive lymphocytes to secondary lymphoid tissues. The contribution of local tertiary lymphoid tissues may be important during influenza infection in ducks. Consistent with leukocyte recruitment, CCL19 and CCL21 transcripts are abundant in lung tissues at 1 day post-infection with highly pathogenic avian influenza A/Vietnam/1203/04 (H5N1) (VN1203). In contrast, expression in lung or intestine tissues infected with low pathogenic A/mallard/BC/500/05 (H5N2) (BC500) is not significant. Recruitment and aggregation of leukocytes is visible in the vicinity of major airways 3 days after infection with VN1203. Chemokine gene expression may serve as a useful marker to evaluate duck immune responses to natural infections and vaccine strains.