Induction of delayed-type hypersensitivity with proteins made insoluble by polymerization

Protein antigens, made particulate by polymerization with ethyl chloroformate, were incorporated in Freund's complete adjuvant and used for footpad immunization of rats and guinea pigs. A comparison was made with animals similarly immunized with the native, soluble protein. Two to three weeks after immunization of rats with polymerized bovine serum albumin (Pol-BSA) and up to 8 weeks after immunization of guinea pigs with polymerized diphtheria toxoid, in vivo and in vitro evidence of delayed-type hypersensitivity (DTH) was found without measurable serum antibodies. Ten times more polymerized than soluble BSA was needed to induce comparable levels of DTH. This was not, however, true in the case of serum antibodies, since soluble BSA induced higher titers than the 1000 times larger amount of Pol-BSA. In addition, the titers in polymer-immunized rats were consistently low or under detectable level when followed up to 5 months after priming. These findings encourage the belief that insolubilization of antigens by polymerization guides the immune response toward cell-mediated immunity, whereas antibody formation becomes weaker. However, boosting of polymer-primed animals with soluble antigen resulted in the production of high levels of antibody.