C3HeB/FeJ mice infected with MAC was associated with increased numbers of CD3+CD4+CD44hi and CD3+CD8+CD44hi activated T effector cells and CD3+CD4+CD44hiCD127+ and CD3+CD8+CD44hiCD127+ memory T cells between 40 and 50 days after infection, followed by diminished numbers. The gene discussed is CD4; the disease is infection.