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Strength of inflammatory stimuli during the early expansion phase plays a crucial role in the effector versus memory cell fate decision of CD8(+) T cells. But it is not known how early lymphocyte distribution after infection has an impact on this process. We demonstrate that the chemokine receptor CXCR3 is involved in promoting CD8(+) T cell commitment to an effector fate rather than a memory fate by regulating T cell recruitment to an antigen/inflammation site. After systemic viral or bacterial infection, the contraction of CXCR3(-/-) antigen-specific CD8(+) T cells is significantly attenuated, resulting in massive accumulation of fully functional memory CD8(+) T cells. Early after infection, CXCR3(-/-) antigen-specific CD8(+) T cells fail to cluster at the marginal zone in the spleen where inflammatory cytokines such as IL-12 and IFN-α are abundant, thus receiving relatively weak inflammatory stimuli. Consequently, CXCR3(-/-) CD8(+) T cells exhibit transient expression of CD25 and preferentially differentiate into memory precursor effector cells as compared with wild-type CD8(+) T cells. This series of events has important implications for development of vaccination strategies to generate increased numbers of antigen-specific memory CD8(+) T cells via inhibition of CXCR3-mediated T cell migration to inflamed microenvironments.

Using transgenic mice that replicate hepatitis B virus (HBV) at high levels in the liver as recipients of HBV-specific cytotoxic T lymphocytes (CTLs), we showed that the chemokines responsive to gamma-2/IFN-gamma inducible protein ([Crg2]IP-10) and monokine induced by interferon-gamma (Mig) are rapidly and strongly induced in the liver after CTL transfer. The transferred CTLs produce neither chemokine; rather, they activate (via the secretion of IFN-gamma) hepatocytes and nonparenchymal cells of the liver to produce (Crg2)IP-10 and Mig. Importantly, blocking these chemokines in vivo reduces the recruitment of host-derived lymphomononuclear cells into the liver and the severity of the liver disease without affecting the IFN-gamma-dependent antiviral potential of the CTLs. The finding that neutralization of these chemokines is associated with maintenance of antiviral effects but diminished tissue damage may be significant for the development of immunotherapeutic approaches for the treatment of chronic HBV infection.

We have previously reported that hepatitis B virus (HBV)-specific CD8(+) cytotoxic T lymphocytes and CD4(+) helper T lymphocytes can inhibit HBV replication in the liver of HBV transgenic mice by secreting interferon (IFN)-gamma when they recognize viral antigen. To determine whether an activated innate immune system can also inhibit HBV replication, in this study we activated natural killer T (NKT) cells in the liver of HBV transgenic mice by a single injection of alpha-galactosylceramide (alpha-GalCer), a glycolipid antigen presented to Valpha14(+)NK1.1(+) T cells by the nonclassical major histocompatibility complex class I-like molecule CD1d. Within 24 h of alpha-GalCer injection, IFN-gamma and IFN-alpha/beta were detected in the liver of HBV transgenic mice and HBV replication was abolished. Both of these events were temporally associated with the rapid disappearance of NKT cells from the liver, presumably reflecting activation-induced cell death, and by the recruitment of activated NK cells into the organ. In addition, prior antibody-mediated depletion of CD4(+) and CD8(+) T cells from the mice did not diminish the ability of alpha-GalCer to trigger the disappearance of HBV from the liver, indicating that conventional T cells were not downstream mediators of this effect. Finally, the antiviral effect of alpha-GalCer was inhibited in mice that are genetically deficient for either IFN-gamma or the IFN-alpha/beta receptor, indicating that most of the antiviral activity of alpha-GalCer is mediated by these cytokines. Based on these results, we conclude that alpha-GalCer inhibits HBV replication by directly activating NKT cells and by secondarily activating NK cells to secrete antiviral cytokines in the liver. In view of these findings, we suggest that, if activated, the innate immune response, like the adaptive immune response, has the potential to control viral replication during natural HBV infection. In addition, the data suggest that therapeutic activation of NKT cells may represent a new strategy for the treatment of chronic HBV infection.

We have previously shown that hepatitis B virus (HBV) replication is abolished in the liver of HBV transgenic mice by inflammatory cytokines induced by HBV-specific cytotoxic T cells and during unrelated viral infections of the liver. We now report that intrahepatic HBV replication is also inhibited in mice infected by the malaria species Plasmodium yoelii 17X NL. P. yoelii infection triggers an intrahepatic inflammatory response characterized by the influx of natural killer cells, macrophages, and T cells. During this process, interferon (IFN)-gamma and IFN-alpha/beta suppress HBV gene expression and replication in the liver. Collectively, the data suggest that malaria infection might influence the course and pathogenesis of HBV infection in coinfected humans.

Antigen presentation by major histocompatibility complex (MHC) class I molecules requires peptide supply by the transporters associated with antigen processing (TAPs), which select substrates in a species- and, in the rat, allele-specific manner. Conflicts between TAPs and MHC preferences for COOH-terminal peptide residues in rodent cells strongly reduce the efficiency of MHC class I antigen presentation. Although human TAP is relatively permissive, some peptide ligands for human histocompatibility leukocyte antigen class I molecules are known to possess very low TAP affinities; the significance of these in vitro findings for cellular antigen presentation is not known. We studied two naturally immunodominant viral epitopes presented by HLA-A2 that display very low affinities for human TAP. Low TAP affinities preclude minimal epitope access to the endoplasmic reticulum (ER) and assembly with HLA-A2 in vitro, as well as presentation by minigene-expressing cells to cytotoxic T lymphocytes. However, NH(2)-terminally but not COOH-terminally extended epitope variants with higher TAP affinities assemble in vitro and are presented to cytotoxic T lymphocytes with high efficiency. Thus, human TAP can influence epitope selection and restrict access to the ER to epitope precursors. Analysis of TAP affinities of a panel of viral epitopes suggests that TAP selection of precursors may be a common phenomenon for HLA-A2-presented epitopes. We also analyzed HLA-A2-eluted peptides from minigene-expressing cells and show that an NH(2)-terminally extended variant with low A2 binding affinity undergoes ER processing, whereas another with high affinity is presented unmodified. Therefore, the previously reported aminopeptidase activity in the ER can also act on TAP-translocated peptides.