Sequential expansion of antibody heterogeneity during the response to bacterial alpha-amylase.

By analyzing antibody heterogeneity during the primary immune response to bacterial a-amylase (B alpha A) in high-responder F1 hybrid mice between C57BL/6 (B6) and C3H/He (C3) mice with the use of isoelectric focusing (IEF), it was shown that the maturation of the primary IgG antibody response consisted of at least two stages. The response of every mouse tested was initiated with the production of specific antibody focused as a limited set of bands in a narrow pH range, and the subsequent rise in antibody titer was associated with the sequential expansion of the spectra involving the appearance of new bands in the pH gradient adjacent to the initial bands. A further rise was accompanied only by intensified staining of the pre-existing bands. These two stages were distinguishable regardless of the antigen dose, although increasing the dose led to widely distributed spectra of focused antibodies and an early shift from the first stage to the second. The sequential expansion of spectra following the appearance of initial antibodies with limited isoelectric point (pI) values was not unique to the anti-BaA antibody response, because similar results were obtained with the antibody response to an immunologically unrelated antigen, Taka-amylase A (TAA). Thus, the appearance of initial antibodies in a limited pH range, overlapping among all F1 hybrids tested, is not a direct reflection of similarity in the determinant specificities of these antibodies among different mice.