CD68 is a 110kD transmembrane glycoprotein of unknown function highly expressed in all cells of the mononuclear phagocyte lineage including monocytes and tissue resident macrophages. It is a type I integral membrane protein with a heavily glycosylated extracellular domain and binds to tissue and organ specific lectins or selectins. CD68 belongs to a growing family of hematopoietic mucin-like molecules, including leukosialin and the lymph node high endothelial ligand for L-selectin GlyCAM- I. The protein is localized to endosome or lysosome-like structure. It is one of 9 genes in a 140kb region of the human chromosome 17p13. Alternative splicing of the gene encoding the protein results in multiple transcripts encoding different isoforms. The protein is highly expressed in bone marrow, colon, small intestine, spleen, testis, trachea and cutaneous T-cell lymphoma.