T Lymphocyte-Secreted Protein I-309 (I-309; CCL1), also known as small inducible cytokine A1, is a small glycoprotein secreted by activated T cells that belongs to a family of inflammatory cytokines known as chemokines. It is chemotactic for monocytes but not for neutrophils. CCL1 attracts monocytes, NK cells, immature B cells, and dendritic cells by interacting with a cell surface chemokine receptor called CCR8.