We have previously shown that adult A/J mice produce high titers of anti-IgE with isotypic or idiotypic specificities in response to challenge with a conjugate of KLH with syngeneic monoclonal IgE. Thus, B cells that can synthesize anti-IgE are present in the mice. Adult mice are unresponsive to unconjugated IgE in CFA, suggesting that tolerance exists at the level of T cells. The present study shows that neonatal mice produce anti-IgE antibodies in response to unconjugated IgE in CFA, but that this capacity is lost after the age of 2-3 wk. The loss of responsiveness corresponds closely with the appearance of detectable IgE in serum, suggesting that the IgE may induce tolerance. The affinities of anti-IgE antibodies produced by neonatal mice fall in the range of values obtained with KLH-IgE in adult mice. Tolerance to unconjugated IgE in CFA can be induced in neonatal mice by administration of IgE in saline. In addition, the tolerant state can be induced by adoptive transfer of spleen cells from adult mice. The time-dependent acquisition of tolerance provides a useful model for studying mechanisms of tolerance and autoimmunity.

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