In order to study how to activate T cells and their immunological characteristics, the anti-CD3 and anti-CD28 McAbs were used to stimulate PBMNC, then their related immunological changes, such as lymphocyte transformation function, the percentage of CD8(+)CD25(+) cells and TGF-beta expression were deleted by lymphocyte transformation assay, flow cytometry and RT-PCR respectively. The results showed that in costimulation with anti-CD28 antibody stimulation, the activity of anti-CD3 antibody was significantly enhanced, the ratio of CD8(+)CD25(+) cells of T cells was obviously increased, while TGF-beta expression was down-regulated. It was concluded that the anti-CD28 antibody costimulation could provide stimulatory signal II, which make T cells more active, while the expression of TGF-beta significantly down-regulated.