The antibody against human CD25, ACT-1, recognizes canine T-lymphocytes in the G2/M and G0/G1 phases of the cell cycle during proliferation.

Because of the lack of an appropriate antibody against the canine CD25 molecule, we investigated whether anti-human CD25 antibody, ACT-1, could be useful in detecting canine T-lymphocyte proliferation. Peripheral mononuclear cells from a dog were cultured for 4 days with or without concanavalin A stimulation. In the last 24 hr, bromodeoxyuridine (BrdU) and human recombinant IL-2 were added. While the cell cycle was detected using anti-BrdU antibody and 7-amino-actinomycine (7-AAD), the cultured cells were stained with anti-canine CD4 antibody and ACT-1. The results showed that T-lymphocytes reactive to ACT-1 were present in the G2/M and G0/G1 phases in 94.4% and 70.0% of CD4-positive T-lymphocytes, respectively, suggesting that flow cytometory with ACT-1 might be useful in detecting canine T-lymphocytes during and after activation.