Modeling the T-helper cell response in acute and chronic hepatitis B virus infection using T-cell receptor transgenic mice

Chronicity following hepatitis B virus (HBV) infection may be maintained by high levels of viral proteins circulating in the serum. To examine the characteristics of T cells capable of co-existing with the secreted hepatitis B e-antigen (HBeAg), T-cell receptor (TCR) transgenic (Tg) mice were produced. To insure that HBeAg-specific T cells would not be deleted in the presence of serum HBeAg, the TCR α and β-chain genes used to produce the TCR-Tg mice were derived from T-cell hybridomas from HBeAg-Tg mice. A TCR-Tg lineage (11/4-12) was produced that possessed a high frequency (∼67%) of CD4⁺ T cells that expressed a TCR-Tg specific for the HBeAg. As predicted, when 11/4-12 TCR-Tg mice were bred with HBeAg-Tg mice no deletion of the HBeAg-specific CD4⁺ T cells occurred in the thymus or the spleen. Functional analysis of the TCR-Tg T cells revealed that the HBeAg-specific CD4⁺ T cells escaped deletion in the thymus and periphery by virtue of low avidity. Regardless of their low avidity, HBeAg-specific TCR-Tg T cells could be activated by exogenous HBeAg as measured by cytokine production in vitro and T-helper cell function for anti-HBe antibody production in vitro and in vivo. Furthermore, activated TCR-Tg HBeAg-specific T cells polarized to the Th₁ subset were able to elicit liver injury when transferred into HBeAg or HBcAg-Tg recipients. Therefore, HBeAg-specific CD4⁺ T cells that can survive deletion or anergy in the presence of circulating HBeAg nonetheless are capable of being activated and of mediating liver injury in vivo.