AimTo study the role of CD4+CD28－T cell and Th1 at the early phase of abdominal aortic aneurysm (AAA).MethodsThe total of 60 cases were recruited in the study,including 30 cases of small AAA and 30 cases of large AAA, 30 healthy controls.Levels of peripheral CD4+ CD28－-T cells were determined by FACS, the serum level of IFN-γ, TNF-α were measured with enzyme-linked immunosorbent assays (ELISA).ResultCompared with healthy controls, the serum level of CD4+CD28－T cells and IFN-γ, TNF-α in AAA patients were higher than that in controls （P<0.05），the expression levels of IFN-γ, TNF-α were positively correlated with the diameter of abdominal aortic.ConclusionExpression levels of CD4+CD28－T cells and IFN- γ were significantly increased in AAA patients, suggesting a potential role of CD4+CD28－T cells and IFN-γ on pathophysiology of AAAs, especially during the early development of AAAs.