Electron microscopy of treponemes subjected to the Treponema pallidum immobilization (TPI) test. II. Immunoelectron microscopy.

The experiments were carried out in order to investigate whether human IgG globulin is absorbed on to the surface of T. pallidum cells during incubation with human syphilis serum in the Treponema pallidum immobilization (TPI) test. Cells of T. pallidum Nichols subjected to the TPI test were further incubated with ferritin conjugated rabbit antihuman IgG globulin. Human IgG globulin could only be demonstrated on immunoimmobilized cells, i.e. cells incubated with human syphilis serum and unheated guinea pig serum (GPS). The surface of the swollen cells was completely covered by a fuzzy layer on to which the ferritin molecules appeared to be attached. In ultrathin sections of cells obtained from the same suspensions the surface of the outer cell membrane was outlined by ferritin molecules. In these cells a rather wide gap was observed between the outer membrane and the cytoplasmic membrane. The ribosomes seemed to have disappeared from the cytoplasm of the immunoimmobilized treponemes, but were present in motile cells obtained from control incubations.