Expansion of neonatal tolerance to self in adult life: I. The role of a bacterial adjuvant in tolerance spread.

T cell neonatal tolerance to self evolves perturbation of the Th1/Th2 balance towards Th2-type self-specific T cells. In the current study we have demonstrated that a tolerant state could be extended to another encephalitogenic determinant only if the neonatally tolerizing determinant was co-administered in adult life with an emulsion of Mycobacterium tuberculosis (i.e. complete Freund's adjuvant). The mechanisms underlying tolerance elicitation and expansion were then explored by an in vitro system in which indirect suppression could be measured. Addition of a tolerizing epitope to splenic T cells from neonatally tolerized animals induced a marked suppression of the anti-MT response. This response could be restored by neutralizing antibodies to IL-4. In contrast, the neutralizing antibodies to IL-4 had no affect on the response of these cells to the tolerizing determinant. These findings are highly significant not only because they explore the important role of microbial antigens in neonatal tolerance, but also because they distinguish, for the first time, between tolerizing and tolerized T cells.