CCR9 and viral infectious disease: In rainbow trout and other fish, homologues for CCR3 and CCR9 have been isolated [46] and analysis showed their expression was significantly upregulated after infection with V. anguillarum. This positive induction may initiate defense responses in the fish cell and contribute to the accumulation and activation of eosinophils and other inflammatory cells at the viral infection site regulating the immune cell migration.