Synthetic Monophosphoryl Lipid A from E. coli (MPLA) is a pure compound produced by chemical synthesis that displays greatly reduced toxicity while maintaining most of the immunostimulatory activity of lipopolysaccharide. MPLA contains 6 fatty acyl groups, while MPLA purified from bacteria contains a mixture of 5, 6,and 7 acyl lipid A. MPLA is a potent stimulator of T cell and antibody responses. MPLA activates TLR4 but does not activate TLR2 reflecting its high purity. It has been used extensively in clinical trials as a component in prophylactic and therapeutic vaccines targeting infectious disease, cancer and allergies.