Abdominal aortic aneurysm (AAA) is a complex chronic disease, whose pathogenesis is associated with the abnormal innate and adaptive immune responses.CD19, a critical cell-surface signal transduction molecule of B cells, is a potent positive regulator and critical for immune responses.We wonder if targeting CDl9 using CD19-neutralizing antibody could protect mice from the development of AAAs.An aorta CaCl2 application-initiated mouse AAA model was used to investigate the role of CD19 in the development of AAAs.We found targeting CD19 attenuated CaCl2-induced formation of AAAs, inflammation and cytokine production in mice.These data indicated that B lymphocytes participate in the pathogenesis of AAA and that depleting B lymphocytes with the CD19-neutralizing antibody is beneficial in the treatment of AAA.Our studies will not only provide insight into the pathogenesis of AAAs but may also lead to the development of novel therapeutic target of CD19.