A role for TGFβ and B cells in immunologic tolerance after intravenous injection of soluble antigen

Background. Intravenous injection of soluble antigen has been reported to induce immunologic tolerance through a variety of mechanisms including T-cell deletion, anergy, and suppression. To clarify the reported discrepancies, we studied mechanisms of intravenous tolerance to a defined transgenic minor transplantation antigen in mice. Methods. Wild-type C57BL6 (B6) mice or congenic B6 B-cell knockout mice were made tolerant to beta -galactosidase (beta -gal). Clinical tolerance was assessed by placement of B6 beta -gal transgenic (tg) and third-party skin grafts. In vitro analysis of T- and B-cell immunity and in vivo treatment with anti-TG beta antibodies were used to define mechanisms of induced tolerance. Results. Intravenous injection of beta -gal induced true immunologic tolerance to beta -gal tg skin in wild-type but not in B-cell-deficient recipients, suggesting that antigen presentation by B cells was required for the effect. The tolerogenic manipulation primed a population of CD4(+), beta -gal-specific, TGF beta -producing T cells. Although evidence for both anergy and suppression were observed, subsequent data demonstrated that TGF beta was a critical immunoregulatory mediator of the tolerant state: neutralizing anti-TGF beta antibodies fully prevented the induction of tolerance to B6 beta -gal tg skin grafts. Second male beta -gal tg grafts placed onto female recipients that were previously made tolerant to female beta -gal tg skin were rapidly rejected, however, suggesting that this TGF beta -induced tolerance could not be linked to additional antigenic determinants. Conclusions. The studies demonstrate a critical role for TGF beta in mediating tolerance after intravenous injection of antigen but additionally raise concerns about the stability of this tolerant state.