Immunological control of macrophage proliferation in vivo.

The transfer of cell-mediated anti-Listeria immunity to normal recipient mice with spleen cells from convalescing donors results in a striking increase in the replication of macrophages in the recipients' livers. Macrophage division occurs 24 h earlier and is 2 to 3 times more intense than macrophage division in mice combating infection with the aid of normal spleen cells. The spleen cells responsible for triggering increased macrophage division and for mediating immunity are destroyed by anti-theta serum and complement, thus showing that they are thymus derived lymphocytes. Their capacity to trigger macrophage division is not realized in the absence of an adequate number of replicating Listeria in the recipients' tissues.