Cationization of protein antigens. I. Alteration of immunogenic properties.

We have shown that a cationized form of bovine serum albumin (BSA) produced by substituting anionic side chain carboxylic groups with aminoethylamide groups possesses unique immunologic properties. The two forms of antigen, native (nBSA) and cationized (cBSA), cross-react at the level of the B cell, as evidenced by the ability of antibody raised against one form to react with the other and by inhibition assays using ELISA. T cell cross-reactivity was also observed in proliferation assays, but the amount of cBSA required for stimulation was 500 times less than the amount of native protein needed. In vivo, cBSA produced responses which, at their optimal levels, were at least double the response to nBSA and which showed a different kinetic pattern, peaking later and lasting longer than the response to the native molecule. Moreover, antibodies were produced in response to administration of cBSA but not nBSA when given i.v. in saline, without an adjuvant. Although a mechanism for these phenomena is not yet clear, we speculate that the cBSA may have a greater affinity for antigen-presenting cells or for the T cell receptor, or that the altered structure may enhance recognition of the molecule by APC and/or helper T cells.