Inhibition of growth of cultured Babesia microti by serum and macrophages in the presence or absence of T cells

Serum and macrophages from the acute-phase (days 12-14 p.i.) and recovery-phase (days 23-25 p.i.) of infection of mice with Babesia microti were analyzed for their ability to inhibit the in vitro growth of B. microti in the presence or absence of T cells. Recovery-phase serum was inhibitory to the growth of B. microti, whereas, acute-phase serum had no inhibitory effects. Both acute- and recovery-phase macrophages inhibited B. microti growth. The co-culture of acute- but not recovery-phase T cells with macrophages from uninfected control mice was inhibitory to the growth of B. microti. Growth of B. microti was also inhibited in cultures containing macrophages from uninfected control mice plus culture supernatant fluid from acute-phase but not recovery-phase T cells. The supernatant fluid from B. microti cultures with acute-phase T cells contained IFN-gamma detected by a sandwich ELISA, whereas cultures with control T cells or recovery phase T cells did not. Results of the present study suggest the likelihood of a protective role against B. microti in mice for antibody which appeared in recovery-phase serum and for macrophages activated by IFN-gamma from acute-phase T cells.