Split tolerance affecting delayed hypersensitivity and induced in mice by pre-immunization with protein antigens in solution.

Adult immunocompetent mice vaccinated with protein antigens in water-in-oil emulsion so as to develop immediate and delayed hypersensitivities resist developing the latter if they are treated with the immunizing antigen in aqueous solution before or during the sensitization period. If the treatments are given during or after vaccination this resistance is directly proportional to their intensity and inversely proportional to the degree of hypersensitivity which has developed when they are begun. But when the treatments are given before vaccination such split tolerance is more pronounced and seems to be directly proportional more to the degree of humoral antibody production existing at the time of vaccination than to the intensity of treatments. The characteristics of this antigenically specific selective unresponsiveness suggest that it may result from a competitive maturation or differentiation of primitive immunocytes: upon exposure to protein antigens in forms not readily able to induce delayed hypersensitivity, the potential functions of these immunocytes for making circulating antibodies may be pre-empted at the expense of such capacity to develop into cells making the antibody of delayed hypersensitivity.