Guinea Pig CCL21 (C-C motif chemokine ligand 21, also known as secondary lymphoid-tissue chemokine, SLC, or 6Ckine) is a homeostatic chemokine that regulates lymphocyte trafficking and organization of adaptive immune responses in guinea pigs (Cavia porcellus). CCL21 primarily signals through the CCR7 receptor, promoting chemotaxis of naïve T cells, central memory T cells, and mature dendritic cells to secondary lymphoid tissues such as lymph nodes and spleen. In guinea pigs, CCL21 is produced by stromal cells and endothelial cells within lymphoid tissues, where it guides immune cells into T-cell zones and supports interactions between antigen-presenting dendritic cells and lymphocytes required for effective activation of adaptive immunity. In guinea pig research, CCL21-mediated CCR7 signaling is particularly relevant in respiratory and infectious disease models, especially tuberculosis (Mycobacterium tuberculosis), where trafficking of dendritic cells and T cells to lymph nodes is critical for antigen presentation and development of protective granulomatous immune responses. Proper regulation of CCL21 contributes to immune surveillance and efficient generation of pathogen-specific T cell responses, while dysregulation may affect lymphoid organization or inflammatory pathology. Because guinea pigs are widely used as translational models for tuberculosis, respiratory infections, and vaccine development, characterization of guinea pig CCL21 supports studies of lymphoid tissue architecture, immune cell migration, and adaptive immune mechanisms relevant to human infectious diseases.