DOTAP DOTAP is a cationic lipid structure, used for in vitro and in vivo nucleic acid and protein delivery. DOTAP is a good immunomodulator, the antigen presenting capacity of antigen presenting cells can be obviously improved by preparing cationic liposome by packaging polypeptide or protein antigens and the DOTAP, and the DOTAP can activate the antigen presenting cells through a mitogen-activated protein kinase (MAP) pathway to induce specific immune response, unlike the traditional adjuvant which activates the antigen presenting cells through a Toll-like receptor pathway.