CCR4 (C-C chemokine receptor type 4, CD194) is a G protein-coupled receptor that binds a number of chemokines including MCP-1 (CCL2), MIP-1 (CCL4), RANTES (CCL5), TARC (CCL17) and macrophage-derived chemokine (CCL22). This receptor is important for the inflammatory response and homeostasis, and may play a regulatory role in central nervous system autoimmunity. CCR4 is often overexpressed in cutaneous T-cell lymphoma where it may contribute to tumor cell survival by inhibiting host immunity. It is also positive in some breast and stomach carcinomas, and it is implicated in melanoma metastasis to the brain, where it is upregulated relative to primary tumors. In immunohistochemistry, CCR4 has membranous and cytoplasmic positivity in various tissues throughout the body. In immune tissues, CCR4 is expressed on platelets, NK cells, monocytes, macrophages, Th17 cells and dendritic cells, and in the brain it is found in Purkinje cells and potentially has low positivity on some astrocytes and microglial cells. References: J Invest Dermatol. 2002 Dec;119(6):1405-10, PMID: 12485447; Cancer Sci. 2011 Jan;102(1):44-50, PMID: 21044233; Breast Cancer Res Treat. 2012 Feb;131(3):837-48, PMID: 21479551; Cancer Sci. 2011 Jul;102(7):1264-71, PMID: 21443538; Oncotarget. 2017 May 9;8(19):31079-31091, PMID: 28415693; Int J Mol Sci. 2017 Nov; 18(11): 2306, PMID: 29099057