The 3.9 monoclonal antibody specifically binds to CD11c, which is also known as Integrin alpha X (αX Integrin/ITGAX), or p150,95 Integrin alpha chain. CD11c is a ~150 kDa type I transmembrane glycoprotein. It is expressed on monocytes, macrophages, granulocytes, NK cells, dendritic cells, and subsets of B and T cells. It associates with CD18 (Integrin beta 2/β2 Integrin) to form the CD11c/CD18 complex, which is also known as p150,95 Integrin, or the Type 4 Complement Receptor (CR4). CD11c/CD18 binds fibrinogen and reportedly serves as a receptor for iC3b and ICAM-1/CD54. CD11c/CD18 functions as an adhesion molecule that mediates cellular binding to ligands expressed on stimulated epithelium and endothelium. The 3.9 monoclonal antibody crossreacts with CD11c expressed by Rhesus macaque leucocytes.