Studies in animal models have demonstrated that solid immunity to
typhus rickettsiae is dependent on immune T cells. In addition, the
surface protein antigen (SPA) of
typhus rickettsiae has been shown to be an effective immunogen, protecting vaccinated animals against subsequent challenge with virulent organisms. In the present studies we describe three classes of human lymphocytes which are capable of lysing cells infected with
typhus rickettsiae. The first class is CD3,8-positive and is capable of specially lysing both HLA-matched and mismatched targets infected with
typhus rickettsiae. Since this cytotoxic effector can be generated with
IL-2 as well as with SPA it appears to be a lymphokine-activated killer (LAK). The second class of lymphocytes is CD3,4-positive and is capable of producing
gamma interferon in response to the SPA of
typhus rickettsiae.
Gamma interferon in turn can cause the lysis of cells infected with
typhus rickettsiae as well as inhibit intracellular rickettsial growth. A third cytotoxic effector which is CD3,4-positive and which is capable of lysing only HLA-matched targets infected with
typhus rickettsiae was generated with a sonicated
antigen, and its fine
antigenic specificity is not known at present. We conclude that the SPA is an immunologically important
protein for the human host and represents an outstanding candidate for a
subunit vaccine against
typhus.