Att-S74-T3Bo-infected calves also developed: (a) monocytosis, neutropenia, and CD4+ lymphopenia in peripheral blood on days 3 to 7 post-inoculation; (b) significant levels of TNFα, CXCL10, IFNγ, IL-4, and IL-10 in sera at day 6 after infection; and (c) IgM and IgG against B. bovis antigens, starting at days 10 and 30 post-inoculation, respectively. Here, CD4 is linked to infection.