Local accumulation and activation of regulatory Foxp3+ CD4 T(R) cells accompanies the appearance of activated CD8 T cells in the liver.

UNLABELLED: Only small populations of nonactivated, nonproliferating Foxp3(+) CD4 regulatory T cell (T(R)) cells are found in the nonparenchymal cell compartment of the mouse liver while liver-draining celiac nodes contain expanded, activated T(R) cell populations (similar to other lymph nodes). Liver Foxp3(+) CD4 T(R) cells suppress activation of T cell responses. Polyclonal, systemic T cell activation in vivo (via anti-CD3 antibody injection) is accompanied by intrahepatic accumulation of T blasts and a rapid but transient intrahepatic increase of activated, proliferating Foxp3(+) CD4 T(R) cells. Following vaccination, the appearance of peripherally primed, specific CD8 T blasts in the liver is preceded by a transient rise of Foxp3(+) CD4 T(R) cells in the liver. The adoptive transfer of immune CD8 T cells into congenic hosts that express the relevant antigen only in the liver leads to the accumulation of specific donor CD8 T cells and of host Foxp3(+) CD4 T(R) cells in the liver. CONCLUSION: Although it contains only a small population of quiescent Foxp3(+) CD4 T(R) cells, the liver can rapidly mobilize and/or recruit this T cell control in response to the intrahepatic appearance of peripherally or locally generated CD8 T blasts.

Type I IFN-induced, NKT cell-mediated negative control of CD8 T cell priming by dendritic cells.

We investigated the negative effect of type I IFN (IFN-I) on the priming of specific CD8 T cell immunity. Priming of murine CD8 T cells is down-modulated if Ag is codelivered with IFN-I-inducing polyinosinic:polycytidylic acid (pI/C) that induces (NK cell- and T/B cell-independent) acute changes in the composition and surface phenotype of dendritic cells (DC). In wild-type but not IFN-I receptor-deficient mice, pI/C reduces the plasmacytoid DC but expands the CD8(+) conventional DC (cDC) population and up-regulates surface expression of activation-associated (CD69, BST2), MHC (class I/II), costimulator (CD40, CD80/CD86), and coinhibitor (PD-L1/L2) molecules by cDC. Naive T cells are efficiently primed in vitro by IFN-I-stimulated CD8 cDC (the key APC involved in CD8 T cell priming) although these DC produced less IL-12 p40 and IL-6. pI/C (IFN-I)-mediated down modulation of CD8 T cell priming in vivo was not observed in NKT cell-deficient CD1d(-/-) mice. CD8 cDC from pI/C-treated mice inefficiently stimulated IFN-gamma, IL-4, and IL-2 responses of NKT cells. In vitro, CD8 cDC that had activated NKT cells in the presence of IFN-I primed CD8 T cells that produced less IFN-gamma but more IL-10. The described immunosuppressive effect of IFN-I thus involves an NKT cell-mediated change in the phenotype of CD8 cDC that favors priming of IL-10-producing CD8 T cells. In the presence of IFN-I, NKT cells hence impair the competence of CD8 cDC to prime proinflammatory CD8 T cell responses.

B7-H1 on hepatocytes facilitates priming of specific CD8 T cells but limits the specific recall of primed responses.

BACKGROUND & AIMS: The requirement for costimulation of CD8 T-cell priming and restimulation by nonprofessional antigen-presenting cells is unresolved. Here, we investigated whether B7-H1 (CD274, PD-L1) on hepatocytes (HC) is involved in the specific activation of naive CD8 T cells or activated CD8 T blasts. METHODS: Naive or activated CD8 T cells from transgenic OT-I mice were primed/restimulated by peptide-pulsed HC, and their proliferation and effector response were determined. We used blocking monoclonal antibodies against B7-H1 and HC from B7-H1-deficient mice to assign a costimulatory or coinhibitory role to B7-H1 for CD8 T-cell priming/restimulation. RESULTS: Blockade of B7-H1 on HC down modulated interferon (IFN)-gamma production and proliferation of HC-primed CD8 T cells, indicating a costimulatory role for B7-H1 in priming CD8 T cells. In contrast, the PD-1/B7-H1 interaction inhibited proliferation and interferon-gamma release of effector/memory CD8 T blasts specifically restimulated by peptide-pulsed HC. CONCLUSIONS: B7-H1 differentially modulates the different stages of the specific CD8 T-cell response triggered by HC, and, whereas it costimulates priming and cytokine responses of naive CD8 T cells, it coinhibits their specific local recall of effector cytokine responses. The interaction of CD8 T cells with B7-H1(+) HC can thus fine-tune proliferative and effector responses of specific CD8 T cells reacting locally to nonprofessional antigen-presenting cells infected with hepatotropic agents.

Type I IFN-producing CD4 Valpha14i NKT cells facilitate priming of IL-10-producing CD8 T cells by hepatocytes.

Upon entering the liver CD8 T cells encounter large numbers of NKT cells patrolling the hepatocyte (HC) surface facing the perisinusoidal space. We asked whether hepatic NKT cells modulate the priming of CD8 T cells by HC. Hepatic (alpha-galactosyl-ceramide-loaded CD1d dimer binding) NKT cells produce predominantly IL-4 when stimulated with glycolipid-presenting HC but predominantly IFN-gamma when stimulated with glycolipid-presenting dendritic cells. These NKT cells prime naive CD8 T cells to a (K(b)-presented) peptide ligand if they simultaneously recognize a CD1d-binding glycolipid presented to them on the surface of the responding CD8 T cells that they prime. No IL-10-producing CD8 T cells are detected if these T cells are primed by either HC or NKT cells. In contrast, IL-10 is produced by HC-primed CD8 T cells if IFN-beta-producing NKT cells are coactivated by the same HC presenting a glycolipid (in the context of CD1d) and an antigenic peptide (in the context of K(b)). Hence, IL-10-producing CD8 T cells are generated in a type I IFN-dependent manner if the three cell types (CD8 T cells, NKT cells, and ligand-presenting HC) specifically and closely interact. IL-10-producing CD8 T cells generated under these conditions down-modulate IL-2 (and proliferative) responses of naive CD4 or CD8 T cells primed by DC. If in close proximity, NKT cells can thus locally modulate the phenotype of CD8 T cells during their priming by HC thereby limiting the local activation of proinflammatory immune effector cells and protecting the liver against immune injury.

Functional adaptive CD4 Foxp3 T cells develop in MHC class II-deficient mice.

CD4 Foxp3 regulatory T (T(R)) cells are well-defined regulator T cells known to develop in the thymus through positive selection by medium-to-high affinity TCR-MHC interactions. We asked whether Foxp3 T(R) cells can be generated in the complete absence of MHC class II molecules. CD4 Foxp3 T(R) cells are found in secondary lymphoid tissues (spleen and lymph nodes) and peripheral tissues (liver) but not the thymus of severely MHC class II-deficient (Aalpha(-/-) B6) mice. These T(R) cells preferentially express CD103 (but not CD25) but up-regulate CD25 surface expression to high levels in response to TCR-mediated activation. MHC class II-independent Foxp3 T(R) cells down modulate vaccine-induced, specific antiviral CD8 T cell responses of Aalpha(-/-) B6 mice in vivo. Furthermore, these T(R) cells suppress IL-2 release and proliferative responses in vitro of naive CD25(-) (CD4 or CD8) T cells from normal B6 mice primed by bead-coupled anti-CD3/anti-CD28 Ab as efficiently as CD4CD25(high) T(R) cells from congenic, normal B6 mice. MHC class II-independent CD4 Foxp3(+) T(R) cells thus preferentially express the (TGF-beta-induced) integrin molecule alpha(E) (CD103), are generated mainly in the periphery and efficiently mediate immunosuppressive effects.

The UBA domains of NUB1L are required for binding but not for accelerated degradation of the ubiquitin-like modifier FAT10.

Proteins selected for degradation are labeled with multiple molecules of ubiquitin and are subsequently cleaved by the 26 S proteasome. A family of proteins containing at least one ubiquitin-associated (UBA) domain and one ubiquitin-like (UBL) domain have been shown to act as soluble ubiquitin receptors of the 26 S proteasome and introduce a new level of specificity into the degradation system. They bind ubiquitylated proteins via their UBA domains and the 26 S proteasome via their UBL domain and facilitate the contact between substrate and protease. NEDD8 ultimate buster-1 long (NUB1L) belongs to this class of proteins and contains one UBL and three UBA domains. We recently reported that NUB1L interacts with the ubiquitin-like modifier FAT10 and accelerates its degradation and that of its conjugates. Here we show that a deletion mutant of NUB1L lacking the UBL domain is still able to bind FAT10 but not the proteasome and no longer accelerates FAT10 degradation. A version of NUB1L lacking all three UBA domains, on the other hand, looses the ability to bind FAT10 but is still able to interact with the proteasome and accelerates the degradation of FAT10. The degradation of a FAT10 mutant containing only the C-terminal UBL domain is also still accelerated by NUB1L, even though the two proteins do not interact. In addition, we show that FAT10 and either one of its UBL domains alone can interact directly with the 26 S proteasome. We propose that NUB1L not only acts as a linker between the 26 S proteasome and ubiquitin-like proteins, but also as a facilitator of proteasomal degradation.