Immunological enhancement is a form of active immunoregulation in which humoral
antibodies suppress primary sensitization or block reaction in sensitized animals. In mouse serum the
antibodies that suppress sensitization in mice (allogeneic enhancement) are predominantly 7Sgamma1 and those that block reaction 7Sgamma2
globulins. But little is known about the identity of xenogeneic
enhancing antibodies, e.g. guinea-pig
antibodies that can suppress sensitization in mice. We have studied these here as specifically effective against induction of
tuberculin-typed
delayed hypersensitivity to chicken
conalbumin antigen. Guinea-pigs required prolonged and intense immunization with
conalbumin to produce readily measurable titres of such
antibodies. Their capacity to suppress mouse sensitization was antigenically specific. Of the three major classes of
antibodies separated from the immunosuppressive guinea-pig
antisera, the
IgG2 globulins were the most effective. These
antibodies lost immunosuppressiveness if digested to either F(ab.)2 or
Fab fragments that retained
antigen-binding capacities. Thus, we provide here an example of xenogeneic antibody-mediated contrasensitization, show that only intact antibody molecules are effective, and demonstrate that immunosuppressiveness is concentrated in different
immunoglobulin classes for xeno- and allogeneically used
antisera.