Identification and characterization of guinea-pig antibodies that contrasensitize in mice

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.