Effect of priming doses of chemically modified antigen on helper activity.

Mice primed with chemically modified bacterial alpha-amylase (BalphaA) [EC 3.2.1.1 alpha-amylase, B. subtilis], which was neither cross-reactive with anti-BalphaA antibody nor able to induce a humoral anti-BalphaA antibody response, developed enhanced responses to a subsequent challenge with native BalphaA (Nakashima et al. (1974) J. Biochem. 76, 349-357). The present studies were designed to examine the relationship of priming doses of BalphaA derivatives to the level of enhancement of the helper activity. Increasing the priming dose of modified antigens resulted in a greater degree of helper cell response until the maximal level of enhancement was reached. When injections for priming and challenge were given intraperitoneally, priming doses of D-BalphaA, M-BalphaA, and RM-BalphaA required for the maximal enhancement of helper activity were about 15, 50, and 15 mug, respectively. Further increase in the priming dose, conversely, resulted in suppressin of the enhanced helper activity, irrespective of whether the time interval between priming and challenge was 10 or 28 days. Suppression of the enhanced helper activity upon excessive dose priming with modified BalphaA derivatives was not specific for the anti-BalphaA antibody response. On the basis of these results it is suggested that this phenomenon of suppression might be partly accounted for by the regulatory mechanism functioning in antigenic competition.