To investigate the dynamics of lymphocyte responses following DTMUV infection in 27-week-old adult laying ducks, the absolute numbers of T helper lymphocyte (Th, CD3+CD4+), cytotoxic T lymphocyte (CTL, CD3+CD8+), and B lymphocyte (CD3-IgY+) subpopulations in the PBMC were analyzed using flow cytometry. The gene discussed is CD4; the disease is infection.