Immunogenic and antigenic epitopes of immunoglobulin--XX. Denaturation of human IgG3 by free radicals.

It has previously been demonstrated that exposure of polyclonal IgG to free radicals results in denaturation evidenced by aggregation, auto-fluorescence and destruction of cysteine, proline and aromatic amino acids. In the present study we have used a panel of monoclonal antibodies (McAb) to epitopes expressed on the IgG3 heavy chain to detect changes in antigenicity. When IgG3 was exposed to u.v. irradiation, as a source of free radicals, subclass specific epitopes were rapidly lost whilst other epitopes were unaffected. Prolonged exposure resulted in further denaturation and a progressive loss of expression of further epitopes. The IgG3 subclass specific McAb are specific to epitopes localized to the hinge region of IgG3. Thus, this exposed cysteine and proline rich region is shown to be particularly vulnerable to free radical attack; however, prolonged exposure results in structural alterations throughout the heavy chain.