Hongwei H. Zhang

Human T Cells That Are Able to Produce IL-17 Express the Chemokine Receptor CCR6

Some pathways of T cell differentiation are associated with characteristic patterns of chemokine receptor expression. A new lineage of effector/memory CD4+ T cells has been identified whose signature products are IL-17 cytokines and whose differentiation requires the nuclear receptor, RORγt. These Th17 cells are critical effectors in mouse models of autoimmune disease. We have analyzed the association between chemokine receptor expression and IL-17 production for human T cells. Activating cord blood (naive) CD4+ T cells under conditions driving Th17 differentiation led to preferential induction of CCR6, CCR9, and CXCR6. Despite these data, we found no strong correlation between the production of IL-17 and expression of CCR9 or CXCR6. By contrast, our analyses revealed that virtually all IL-17-producing CD4+ T cells, either made in our in vitro cultures or found in peripheral blood, expressed CCR6, a receptor found on ∼50% of CD4+ memory PBL. Compared with CD4+CD45RO+CCR6− cells, CD4+CD45RO+CCR6+ cells contained at least 100-fold more IL-17A mRNA and secreted 100-fold more IL-17 protein. The CCR6+ cells showed a similar enrichment in mRNA for RORγt. CCR6 was likewise expressed on all IL-17-producing CD8+ PBL. CCR6 has been associated with the trafficking of T, B, and dendritic cells to epithelial sites, but has not been linked to a specific T cell phenotype. Our data reveal a fundamental feature of IL-17-producing human T cells and a novel role for CCR6, suggesting both new directions for investigating IL-17-related immune responses and possible targets for preventing inflammatory injury.

CCR6 is required for IL-23–induced psoriasis-like inflammation in mice

Psoriasis is a common immune-mediated chronic inflammatory skin disorder, but the mechanisms of pathogenesis are still poorly understood. IL-23 is expressed in psoriatic skin, and IL-23 injection produces IL-22-dependent psoriasiform changes in mouse skin. Th17 cells produce IL-22 and display CCR6, the CCL20 receptor; CCR6+ T cells and CCL20 are abundant in psoriatic skin. We investigated a possible role for CCR6 in recruiting Th17 cells and producing psoriasiform pathology by injecting IL-23 into the skin of WT and Ccr6-/- mice. Unlike for WT mice, IL-23-injected ears of Ccr6-/- mice showed neither substantial epidermal/dermal changes nor increased Il22 mRNA expression. However, injection of IL-22 yielded equivalent psoriasiform changes in WT and Ccr6-/- mice. Surprisingly, IL-23-injected ears of WT and Ccr6-/- mice contained similar numbers of Th cells able to make IL-17A and/or IL-22. Furthermore, in ears of Rag1-/- mice, IL-23 initially induced skin changes and levels of Il22 mRNA that were indistinguishable from WT mice, revealing at least one non-T cell source for IL-22. We conclude that CCR6 is essential in a model of IL-23-induced, IL-22-mediated dermatitis, which develops in sequential T cell-independent and T cell-dependent phases. These findings reveal an expanded role for CCR6 in IL-23-related responses and identify CCR6 as a potential therapeutic target in psoriasis.

The CXC Chemokine Murine Monokine Induced by IFN-γ (CXC Chemokine Ligand 9) Is Made by APCs, Targets Lymphocytes Including Activated B Cells, and Supports Antibody Responses to a Bacterial Pathogen In Vivo

Monokine induced by IFN-γ (Mig; CXC chemokine ligand 9) is an IFN-γ-inducible CXC chemokine that signals through the receptor CXCR3 and is known to function as a chemotactic factor for human T cells, particularly following T cell activation. The mig gene can be induced in multiple cell types and organs, and Mig has been shown to contribute to T cell infiltration into immune/inflammatory reactions in peripheral tissues in mice. We have investigated the expression and activities of Mig and CXCR3 in mouse cells and the role of Mig in models of host defense in mice. Murine (Mu)Mig functioned as a chemotactic factor for resting memory and activated T cells, both CD4+ and CD8+, and responsiveness to MuMig correlated with surface expression of MuCXCR3. Using mig−/− mice, we found that MuMig was not necessary for survival after infections with a number of intracellular pathogens. Surprisingly, however, we found that mig−/− mice showed reductions of 50–75% in Abs produced against the intracellular bacterium Francisella tularensis live vaccine strain. Furthermore, we found that MuMig induced both calcium signals and chemotaxis in activated B cells, and that B cell activation induced expression of MuCXCR3. In addition, IFN-γ induced the expression of mumig in APCs, including CD8α+ and CD8α− dendritic cells. Together, our data suggest that Mig and CXCR3 may be important not only to recruit T cells to peripheral inflammatory sites, but also in some cases to maximize interactions among activated T cells, B cells, and dendritic cells within lymphoid organs to provide optimal humoral responses to pathogens.

Characterization of subsets of CD4+ memory T cells reveals early branched pathways of T cell differentiation in humans

The pathways for differentiation of human CD4+ T cells into functionally distinct subsets of memory cells in vivo are unknown. The identification of these subsets and pathways has clear implications for the design of vaccines and immune-targeted therapies. Here, we show that populations of apparently naïve CD4+ T cells express the chemokine receptors CXCR3 or CCR4 and demonstrate patterns of gene expression and functional responses characteristic of memory cells. The proliferation history and T cell receptor repertoire of these chemokine-receptor+ cells suggest that they are very early memory CD4+ T cells that have “rested down” before acquiring the phenotypes described for “central” or “effector” memory T cells. In addition, the chemokine-receptor+ “naïve” populations contain Th1 and Th2 cells, respectively, demonstrating that Th1/Th2 differentiation can occur very early in vivo in the absence of markers conventionally associated with memory cells. We localized ligands for CXCR3 and CCR4 to separate foci in T cell zones of tonsil, suggesting that the chemokine-receptor+ subsets may be recruited and contribute to segregated, polarized microenvironments within lymphoid organs. Importantly, our data suggest that CD4+ T cells do not differentiate according to a simple schema from naïve → CD45RO+ noneffector/central memory → effector/effector memory cells. Rather, developmental pathways branch early on to yield effector/memory populations that are highly heterogeneous and multifunctional and have the potential to become stable resting cells.

CCR2 Identifies a Stable Population of Human Effector Memory CD4+ T Cells Equipped for Rapid Recall Response

Because T cells act primarily through short-distance interactions, homing receptors can identify colocalizing cells that serve common functions. Expression patterns for multiple chemokine receptors on CD4+ T cells from human blood suggested a hierarchy of receptors that are induced and accumulate during effector/memory cell differentiation. We characterized CD4+CD45RO+ T cells based on expression of two of these receptors, CCR5 and CCR2, the principal subsets being CCR5−CCR2− (∼70%), CCR5+CCR2− (∼25%), and CCR5+CCR2+ (∼5%). Relationships among expression of CCR5 and CCR2 and CD62L, and the subsets’ proliferation histories, suggested a pathway of progressive effector/memory differentiation from the CCR5−CCR2− to CCR5+CCR2− to CCR5+CCR2+ cells. Sensitivity and rapidity of TCR-mediated activation, TCR signaling, and effector cytokine production by the subsets were consistent with such a pathway. The subsets also showed increasing responsiveness to IL-7, and the CCR5+CCR2+ cells were CD127bright and invariably showed the greatest response to tetanus toxoid. CCR5+CCR2+ cells also expressed the largest repertoire of chemokine receptors and migrated to the greatest number of chemokines. By contrast, the CCR5+CCR2− cells had the greatest percentages of regulatory T cells, activated/cycling cells, and CMV-reactive cells, and were most susceptible to apoptosis. Our results indicate that increasing memory cell differentiation can be uncoupled from susceptibility to death, and is associated with an increase in chemokine responsiveness, suggesting that vaccination (or infection) can produce a stable population of effector-capable memory cells that are highly enriched in the CCR5+CCR2+ subset and ideally equipped for rapid recall responses in tissue.

Conventional NK Cells Can Produce IL-22 and Promote Host Defense in Klebsiella pneumoniae Pneumonia

It was reported that host defense against pulmonary Klebsiella pneumoniae infection requires IL-22, which was proposed to be of T cell origin. Supporting a role for IL-22, we found that Il22−/− mice had decreased survival compared with wild-type mice after intratracheal infection with K. pneumoniae. Surprisingly, however, Rag2−/− mice did not differ from wild-type mice in survival or levels of IL-22 in the lungs postinfection with K. pneumoniae. In contrast, K. pneumoniae–infected Rag2−/−Il2rg−/− mice failed to produce IL-22. These data suggested a possible role for NK cells or other innate lymphoid cells in host defense and production of IL-22. Unlike NK cell–like innate lymphoid cells that produce IL-22 and display a surface phenotype of NK1.1−NKp46+CCR6+, lung NK cells showed the conventional phenotype, NK1.1+NKp46+CCR6−. Mice depleted of NK cells using anti–asialo GM1 showed decreased survival and higher lung bacterial counts, as well as increased dissemination of K. pneumoniae to blood and liver, compared with control-treated mice. NK cell depletion also led to decreased production of IL-22 in the lung. Within 1 d postinfection, although there was no increase in the number of lung NK cells, a subset of lung NK cells became competent to produce IL-22, and such cells were found in both wild-type and Rag2−/− mice. Our data suggest that, during pulmonary infection of mice with K. pneumoniae, conventional NK cells are required for optimal host defense, which includes the production of IL-22.

PLZF Regulates CCR6 and Is Critical for the Acquisition and Maintenance of the Th17 Phenotype in Human Cells

Th17 cells, which express the chemokine receptor CCR6, are implicated in many immune-mediated disorders, such as psoriasis and multiple sclerosis. We found that expression levels of CCR6 on human effector/memory CD4+ T cells reflect a continuum of Th17 differentiation. By evaluating the transcriptome in cells with increasing CCR6, we detected progressive upregulation of ZBTB16, which encodes the broad complex, tramtrack, bric-à-brac–zinc finger transcription factor promyelocytic leukemia zinc finger protein (PLZF). Using chromatin immunoprecipitation for modified histones, p300, and PLZF, we identified enhancer-like sites at −9/−10 and −13/−14 kb from the upstream transcription start site of CCR6 that bind PLZF in CCR6+ cells. For Th cells from adult blood, both in the CCR6+ memory population and in naive cells activated ex vivo, knockdown of ZBTB16 downregulated CCR6 and other Th17-associated genes. ZBTB16 and RORC (which encodes the “master regulator” RORγt) cross-regulate each other, and PLZF binds at the RORC promoter in CCR6+ cells. In naive Th cells from cord blood, ZBTB16 expression was confined to CD161+ cells, which are Th17 cell precursors. ZBTB16 was not expressed in mouse Th17 cells, and Th17 cells could be made from luxoid mice, which harbor an inactivating mutation in Zbtb16. These studies demonstrate a role for PLZF as an activator of transcription important both for Th17 differentiation and the maintenance of the Th17 phenotype in human cells, expand the role of PLZF as a critical regulator in the human adaptive immune system, and identify a novel, essential element in a regulatory network that is of significant therapeutic interest.

Pathway-selective suppression of chemokine receptor signaling in B cells by LPS through downregulation of PLC-β2

Lymphocyte activation leads to changes in chemokine receptor expression. There are limited data, however, on how lymphocyte activators can alter chemokine signaling by affecting downstream pathways. We hypothesized that B cell-activating agents might alter chemokine responses by affecting downstream signal transducers, and that such effects might differ depending on the activator. We found that activating mouse B cells using either anti-IgM or lipopolysaccharide (LPS) increased the surface expression of CCR6 and CCR7 with large increases in chemotaxis to their cognate ligands. By contrast, while anti-IgM also led to enhanced calcium responses, LPS-treated cells showed only small changes in calcium signaling as compared with cells that were freshly isolated. Of particular interest, we found that LPS caused a reduction in the level of B-cell phospholipase C (PLC)-β2 mRNA and protein. Data obtained using PLC-β2−/− mice showed that the β2 isoform mediates close to one-half the chemokine-induced calcium signal in resting and anti-IgM-activated B cells, and we found that calcium signals in the LPS-treated cells were boosted by increasing the level of PLC-β2 using transfection, consistent with a functional effect of downregulating PLC-β2. Together, our results show activator-specific effects on responses through B-cell chemokine receptors that are mediated by quantitative changes in a downstream signal-transducing protein, revealing an activity for LPS as a downregulator of PLC-β2, and a novel mechanism for controlling chemokine-induced signals in lymphocytes.

Differentiation of Human T Cells Alters Their Repertoire of G Protein α-Subunits

Because T cell differentiation leads to an expanded repertoire of chemokine receptors, a subgroup of G protein-coupled receptors, we hypothesized that the repertoire of G proteins might be altered in parallel. We analyzed the abundance of mRNA and/or protein of six G protein α-subunits in human CD4+ and CD8+ T cell subsets from blood. Although most G protein α-subunits were similarly expressed in all subsets, the abundance of Gαo, a protein not previously described in hematopoietic cells, was much higher in memory versus naive cells. Consistent with these data, activation of naive CD4+ T cells in vitro significantly increased the abundance of Gαo in cells stimulated under nonpolarizing or TH17 (but not TH1 or TH2)-polarizing conditions. In functional studies, the use of a chimeric G protein α-subunit, Gαqo5, demonstrated that chemokine receptors could couple to Gαo-containing G proteins. We also found that Gαi1, another α-subunit not described previously in leukocytes, was expressed in naive T cells but virtually absent from memory subsets. Corresponding to their patterns of expression, siRNA-mediated knockdown of Gαo in memory (but not naive) and Gαi1 in naive (but not memory) CD4+ T cells inhibited chemokine-dependent migration. Moreover, although even in Gαo- and Gαi1-expressing cells mRNAs of these α-subunits were much less abundant than Gαi2 or Gαi3, knockdown of any of these subunits impaired chemokine receptor-mediated migration similarly. Together, our data reveal a change in the repertoire of Gαi/o subunits during T cell differentiation and suggest functional equivalence among Gαi/o subunits irrespective of their relative abundance.

Changes in histone acetylation and methylation that are important for persistent but not transient expression of CCR4 in human CD4+ T cells

Although regulation of CXCR3 and CCR4 is related to Th1 and Th2 differentiation, respectively, many CXCR3+ and CCR4+ cells do not express IFN‐γ and/or IL‐4, suggesting that the chemokine receptor genes might be inducible by mechanisms that are lineage‐independent. We investigated the regulation of CXCR3 versus IFNG, and CCR4 versus IL4 in human CD4+ T cells by analyzing modifications of histone H3. In naïve cord‐blood cells, under nonpolarizing conditions not inducing IL4, CCR4 was induced to high levels without many of the activation‐associated changes in promoter histone H3 found for both IL4 and CCR4 in Th2 cells. Importantly, CCR4 expression was stable in Th2 cells, but fell in nonpolarized cells after the cells were rested; this decline could be reversed by increasing histone acetylation using sodium butyrate. Patterns of histone H3 modifications in CXCR3+CCR4− and CXCR3−CCR4+ CD4+ T‐cell subsets from adult blood matched those in cells cultured under polarizing conditions in vitro. Our data show that high‐level lineage‐independent induction of CCR4 can occur following T‐cell activation without accessibility‐associated changes in histone H3, but that without such changes expression is transient rather than persistent.