RESUMO
Chronic infection is difficult to overcome because of exhaustion or depletion of cytotoxic effector CD8(+) T cells (cytotoxic T lymphoytes (CTLs)). Here we report that signaling via Toll-like receptors (TLRs) induced intrahepatic aggregates of myeloid cells that enabled the population expansion of CTLs (iMATEs: 'intrahepatic myeloid-cell aggregates for T cell population expansion') without causing immunopathology. In the liver, CTL proliferation was restricted to iMATEs that were composed of inflammatory monocyte-derived CD11b(+) cells. Signaling via tumor-necrosis factor (TNF) caused iMATE formation that facilitated costimulation dependent on the receptor OX40 for expansion of the CTL population. The iMATEs arose during acute viral infection but were absent during chronic viral infection, yet they were still induced by TLR signaling. Such hepatic expansion of the CTL population controlled chronic viral infection of the liver after vaccination with DNA. Thus, iMATEs are dynamic structures that overcome regulatory cues that limit the population expansion of CTLs during chronic infection and can be used in new therapeutic vaccination strategies.
Assuntos
Linfócitos T CD8-Positivos/imunologia , Proliferação de Células , Hepatopatias/imunologia , Coriomeningite Linfocítica/imunologia , Células Mieloides/imunologia , Linfócitos T Citotóxicos/imunologia , Animais , Animais Recém-Nascidos , Antígeno CD11b/imunologia , Antígeno CD11b/metabolismo , Linfócitos T CD8-Positivos/metabolismo , Doença Crônica , Citometria de Fluxo , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Interações Hospedeiro-Patógeno/imunologia , Imunoterapia , Fígado/imunologia , Fígado/metabolismo , Fígado/virologia , Hepatopatias/terapia , Hepatopatias/virologia , Coriomeningite Linfocítica/terapia , Coriomeningite Linfocítica/virologia , Vírus da Coriomeningite Linfocítica/imunologia , Vírus da Coriomeningite Linfocítica/fisiologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Microscopia Confocal , Células Mieloides/metabolismo , Receptores OX40/imunologia , Receptores OX40/metabolismo , Transdução de Sinais/imunologia , Linfócitos T Citotóxicos/metabolismo , Receptor Toll-Like 9/imunologia , Receptor Toll-Like 9/metabolismoRESUMO
The liver bears unique immune properties that support both immune tolerance and immunity, but the mechanisms responsible for clearance versus persistence of virus-infected hepatocytes remain unclear. Here, we dissect the factors determining the outcome of antiviral immunity using recombinant adenoviruses that reflect the hepatropism and hepatrophism of hepatitis viruses. We generated replication-deficient adenoviruses with equimolar expression of ovalbumin, luciferase, and green fluorescent protein driven by a strong ubiquitous cytomegalovirus (CMV) promoter (Ad-CMV-GOL) or by 100-fold weaker, yet hepatocyte-specific, transthyretin (TTR) promoter (Ad-TTR-GOL). Using in vivo bioluminescence to quantitatively and dynamically image luciferase activity, we demonstrated that Ad-TTR-GOL infection always persists, whereas Ad-CMV-GOL infection is always cleared, independent of the number of infected hepatocytes. Failure to clear Ad-TTR-GOL infection involved mechanisms acting during initiation as well as execution of antigen-specific immunity. First, hepatocyte-restricted antigen expression led to delayed and curtailed T-cell expansion-10,000-fold after Ad-CMV-GOL versus 150-fold after Ad-TTR-GOL-infection. Second, CD8 T-cells primed toward antigens selectively expressed by hepatocytes showed high PD-1/Tim-3/LAG-3/CTLA-4/CD160 expression levels similar to that seen in chronic hepatitis B. Third, Ad-TTR-GOL but not Ad-CMV-GOL-infected hepatocytes escaped being killed by effector T-cells while still inducing high PD-1/Tim-3/LAG-3/CTLA-4/CD160 expression, indicating different thresholds of T-cell receptor signaling relevant for triggering effector functions compared with exhaustion. Conclusion: Our study identifies deficits in the generation of CD8 T-cell immunity toward hepatocyte-expressed antigens and escape of infected hepatocytes expressing low viral antigen levels from effector T-cell killing as independent factors promoting viral persistence. This highlights the importance of addressing both the restauration of CD8 T-cell dysfunction and overcoming local hurdles of effector T-cell function to eliminate virus-infected hepatocytes.