Antigen dose-dependent predominance of either direct or sequential switch in IgE antibody responses.

Priming of CBA/J mice with minute doses of protein antigens (Ag) leads to high IgE antibody (Ab) titres in the immune sera of these animals. In contrast priming with large doses elicits only a marginal production of IgE Ab. In vitro restimulation of spleen cells from animals primed with large doses and lacking in vivo IgE Ab leads to a burst of IgE Ab-forming cells. This in vitro anamnestic response is lacking in mice primed with minute doses of Ag. In order to trace the cellular basis of the in vitro IgE memory response we have extended the analysis of the distribution of Ab isotypes to Ag-primed IgG1-deficient delta 5'S gamma 1 mice. The data presented here must be interpreted as followed. Priming of mice with minute doses of Ag leads to a direct switch from IgM to IgE Ab expression in both strains. These animals have high IgE Ab titres without establishing an IgE memory. The direct switch was verified by polymerase chain reaction and Southern blot analysis of switch circle DNA isolated from Ag-specific B cells of CBA/J mice primed with minute doses of Ag. In contrast to immunization with minute doses, priming with large doses of Ag fails to induce in vivo IgE Ab production in CBA/J and delta 5'S gamma 1 mice but establishes a B epsilon memory in CBA/J mice which involves IgG1-bearing intermediate B cells. In vivo these B epsilon memory cells do not enter the status of IgE Ab-producing cells. In vitro they can be released from this anergy and presumed suppression and develop in an anamnestic response into a large population of IgE Ab-forming B cells. This increase in the number of IgE Ab-producing cells after restimulation in vitro is lacking in delta 5'S gamma 1 mice, apparently because of their inability to generate IgG1-expressing precursor cells. The notion of a sequential switch and an IgG1 intermediate B epsilon memory status is also supported by depletion and inhibition experiments. Elimination of IgG1-expressing B cells in CBA/J mice primed with high doses of Ag prevents the IgE Ab burst after in vitro challenge with Ag. The data further suggest that the two switch pathways are not mutually exclusive and that the Ag dose can decide which pathway is preferentially used.