Mallard CCL19 (C-C motif chemokine ligand 19), also referred to as macrophage inflammatory protein-3β (MIP-3β) or EBI1 ligand chemokine (ELC)-like in avian species, is a member of the CC chemokine family that regulates lymphocyte trafficking and organization of secondary lymphoid tissues in mallards (Anas platyrhynchos). CCL19 is expressed primarily by stromal cells, dendritic cells, and macrophages within lymphoid organs such as the spleen, thymus, and gut-associated lymphoid tissues. It functions through a CCR7-like receptor to direct migration of naïve T cells and mature dendritic cells to lymphoid tissues, facilitating antigen presentation and initiation of adaptive immune responses. In healthy mallards, CCL19 contributes to immune surveillance and maintenance of lymphoid architecture; expression may increase during viral or bacterial infection, vaccination, or inflammatory stimulation. In avian and wildlife immunology research, mallard CCL19 is particularly relevant in studies of host responses to avian influenza virus and other waterfowl-associated pathogens, as mallards serve as natural reservoirs for multiple influenza A virus strains. Characterization of CCL19 in mallards provides insight into CCR7-mediated immune cell trafficking, adaptive immune activation, and host–pathogen interactions in wild and domestic waterfowl populations.