CD68 (macrosialin) is a transmembrane glycoprotein of the LAMP family found in monocytes and macrophages. CD68 functions in antigen processing and in protecting the cell surface from hydrolytic enzymes. In immunohistochemistry, CD68 shows membranous expression in macrophages, monocytes, mast cells, plasmacytoid T cells within reactive lymph nodes, mononuclear phagocytes, and myeloid cells such as granulocytes. As a marker in cancer and disease, CD68 is positive in AML, CML, histiocytic neoplasms, melanomas, and some B-cell small lymphocytic lymphomas. Hairy-cell leukemias can also be weakly positive for CD68. References: Proc Natl Acad Sci U S A. 1996 Dec 10; 93(25): 14833–14838, PMID: 8962141; Lab Invest. 2017 Jan;97(1):4-13. doi: 10.1038/labinvest.2016.116. Epub 2016 Nov 21, PMID: 27869795