A monoclonal antibody specific for BK virus large T-antigen (clone BK.T-1) also binds the human Ku autoantigen

A monoclonal antibody directed against the BK virus large T-antigen (clone BK.T-1) has previously been used to evaluate BKV-T antigen (BKV-TAg) expression. However, our experience showed a consistent reactivity to uninfected human, but not rodent cells and tissues. Using immunoprecipitation, Western analysis, amino acid sequencing and end-point dilution analysis, we analysed the BK.T-1 antibody reactivity and identified the bound cellular protein. The results clearly show that the antibody recognizes the large subunit (Ku86) of the Ku autoantigen, the regulatory component of the DNA-PKcs. We also demonstrated that the antibody retained its original reactivity in BKV-TAg transformed hamster kidney cells. The cross-reaction of the BK.T-1 antibody suggests a possible similarity between BKV-TAg and Ku86, but makes the antibody unsuitable for studies of BKV large T-antigen in the human cells.