CCL13 (C-C motif chemokine ligand 13), also known as MCP-4, is a chemotactic cytokine that attracts monocytes, lymphocytes, basophils, and eosinophils through CCR2B and CCR3 receptors 1. CCL13 plays a significant role in inflammatory skin diseases, particularly atopic dermatitis and psoriasis. In atopic dermatitis, CCL13 is expressed by M2 macrophages in leukocyte-infiltrated areas and represents one of the top upregulated proteins in disease lesions 23. Single-cell analyses demonstrate that CCL13-expressing macrophages participate in complex cellular interactions with fibroblasts, dendritic cells, and T cells in inflamed skin 2. In psoriasis, SFRP2+ fibroblasts produce CCL13 as part of a pro-inflammatory communication network involving CCR2+ myeloid cells 4. CCL13 also contributes to rheumatoid arthritis pathogenesis, with elevated expression in synovial myeloid cells of ACPA-negative patients compared to ACPA-positive patients 5. Therapeutically, CCL13 serves as a biomarker for treatment response, as dupilumab therapy significantly reduces CCL13 levels in atopic dermatitis patients, reflecting normalization of IL-4/IL-13 downstream activity 67. Beyond inflammatory diseases, CCL13 has documented roles in cancer, atherosclerosis, and various other human diseases 81.