Liv Eidsmo

Memory T cells in nonlymphoid tissue that provide enhanced local immunity during infection with herpes simplex virus

Effective immunity is dependent on long-surviving memory T cells. Various memory subsets make distinct contributions to immune protection, especially in peripheral infection. It has been suggested that T cells in nonlymphoid tissues are important during local infection, although their relationship with populations in the circulation remains poorly defined. Here we describe a unique memory T cell subset present after acute infection with herpes simplex virus that remained resident in the skin and in latently infected sensory ganglia. These T cells were in disequilibrium with the circulating lymphocyte pool and controlled new infection with this virus. Thus, these cells represent an example of tissue-resident memory T cells that can provide protective immunity at points of pathogen entry.

Cross-presentation of viral and self antigens by skin-derived CD103 + dendritic cells

Skin-derived dendritic cells (DCs) include Langerhans cells, classical dermal DCs and a langerin-positive CD103+ dermal subset. We examined their involvement in the presentation of skin-associated viral and self antigens. Only the CD103+ subset efficiently presented antigens of herpes simplex virus type 1 to naive CD8+ T cells, although all subsets presented these antigens to CD4+ T cells. This showed that CD103+ DCs were the migratory subset most efficient at processing viral antigens into the major histocompatibility complex class I pathway, potentially through cross-presentation. This was supported by data showing only CD103+ DCs efficiently cross-presented skin-derived self antigens. This indicates CD103+ DCs are the main migratory subtype able to cross-present viral and self antigens, which identifies another level of specialization for skin DCs.

Splenic accumulation of IL-10 mRNA in T cells distinct from CD4+CD25+ (Foxp3) regulatory T cells in human visceral leishmaniasis.

Visceral leishmaniasis (VL) is a life-threatening disease characterized by uncontrolled parasitization of the spleen, liver, and bone marrow. Interleukin (IL)-10 has been implicated in the suppression of host immunity in human VL based on the elevated levels of IL-10 observed in plasma and lesional tissue, and its role in preventing clearance of Leishmania donovani in murine models of VL. The aim of this study was to identify the cellular source of IL-10 in human VL and determine if CD4+CD25+ (Foxp3high) regulatory T (T reg) cells are associated with active disease. We analyzed surface marker and gene expression in peripheral blood mononuclear cells and splenic aspirates from Indian VL patients before and 3–4 wk after treatment with Amphotericin B. The results did not point to an important role for natural CD4+CD25+ (Foxp3high) T reg cells in human VL. They did not accumulate in and were not a major source of IL-10 in the spleen, and their removal did not rescue antigen-specific interferon γ responses. In contrast, splenic T cells depleted of CD25+ cells expressed the highest levels of IL-10 mRNA and were the predominant lymphocyte population in the VL spleen. The elevated levels of IL-10 in VL plasma significantly enhanced the growth of L. donovani amastigotes in human macrophages. The data implicate IL-10–producing CD25−Foxp3− T cells in the pathogenesis of human VL.

MiR-155 is overexpressed in patients with atopic dermatitis and modulates T-cell proliferative responses by targeting cytotoxic T lymphocyte–associated antigen 4

BACKGROUND MicroRNAs (miRNAs) are short noncoding RNAs that suppress gene expression at the posttranscriptional level. Atopic dermatitis is a common chronic inflammatory skin disease characterized by the presence of activated T cells within the skin. OBJECTIVE We sought to explore the role of miRNAs in the pathogenesis of atopic dermatitis. METHODS Global miRNA expression in healthy and lesional skin of patients with atopic dermatitis was compared by using TaqMan MicroRNA Low Density Arrays. miR-155 expression in tissues and cells was quantified by means of quantitative real-time PCR. The cellular localization of miR-155 was analyzed by means of in situ hybridization. The regulation of cytotoxic T lymphocyte-associated antigen (CTLA-4) by miR-155 was investigated by using luciferase reporter assays and flow cytometry. CTLA-4 expression and functional assays were performed on T(H) cells overexpressing miR-155. RESULTS miR-155 was one of the highest-ranked upregulated miRNAs in patients with atopic dermatitis. In the skin miR-155 was predominantly expressed in infiltrating immune cells. miR-155 was upregulated during T-cell differentiation/activation and was markedly induced by T-cell activators in PBMCs in vitro and by superantigens and allergens in the skin in vivo. CTLA-4, an important negative regulator of T-cell activation, was identified as a direct target of miR-155. Overexpression of miR-155 in T(H) cells resulted in decreased CTLA-4 levels accompanied by an increased proliferative response. CONCLUSION miR-155 is significantly overexpressed in patients with atopic dermatitis and might contribute to chronic skin inflammation by increasing the proliferative response of T(H) cells through the downregulation of CTLA-4.

Composition of Innate Lymphoid Cell Subsets in the Human Skin: Enrichment of NCR+ ILC3 in Lesional Skin and Blood of Psoriasis Patients

Innate lymphoid cells (ILCs) are increasingly appreciated as important regulators of tissue homeostasis and inflammation. However, their role in human skin remains obscure. We found that healthy peripheral blood CD117(+) ILC3, lacking the natural cytotoxicity receptor (NCR) NKp44 (NCR(-) ILC3), CD117(-)NCR(-)CRTH2(-)CD161(+) ILC1, and CRTH2(+) ILC2, express the skin-homing receptor cutaneous lymphocyte antigen (CLA). NCR(+) ILC3 were scarce in peripheral blood. Consistently, we identified in normal skin ILC2 and NCR(-) ILC3, a small proportion of CD161(+) ILC1, and hardly any NCR(+) ILC3, whereas NCR(+) ILC3 were present in cultured dermal explants. The skin ILC2 and NCR(+) ILC3 subsets produced IL-13 and IL-22, respectively, upon cytokine stimulation. Remarkably, dermal NCR(-) ILC3 converted to NCR(+) ILC3 upon culture in IL-1β plus IL-23, cytokines known to be involved in psoriatic inflammation. In line with this observation, significantly increased proportions of NCR(+) ILC3 were present in lesional skin and peripheral blood of psoriasis patients as compared with skin and blood of healthy individuals, respectively, whereas the proportions of ILC2 and CD161(+) ILC1 remained unchanged. NCR(+) ILC3 from skin and blood of psoriasis patients produced IL-22, which is regarded as a key driver of epidermal thickening, suggesting that NCR(+) ILC3 may participate in psoriasis pathology.

MiR-125b, a MicroRNA Downregulated in Psoriasis, Modulates Keratinocyte Proliferation by Targeting FGFR2

MicroRNAs (miRNAs) are short, single-stranded, noncoding RNAs that play important roles in the regulation of gene expression. We previously identified a characteristic miRNA expression profile in psoriasis, distinct from that of healthy skin. One of the most downregulated miRNAs in psoriasis skin was microRNA-125b (miR-125b). In this study, we aimed to identify the potential role(s) of miR-125b in psoriasis pathogenesis. In situ hybridization results showed that the major cell type responsible for decreased miR-125b levels in psoriasis lesions was the keratinocyte. Overexpression of miR-125b in primary human keratinocytes suppressed proliferation and induced the expression of several known differentiation markers. Conversely, inhibition of endogenous miR-125b promoted cell proliferation and delayed differentiation. Fibroblast growth factor receptor 2 (FGFR2) was identified as one of the direct targets for suppression by miR-125b by luciferase reporter assay. The expression of miR-125b and FGFR2 was inversely correlated in both transfected keratinocytes and in psoriatic skin. Knocking down FGFR2 expression by siRNA suppressed keratinocyte proliferation, but did not enhance differentiation. Altogether, our results demonstrate a role for miR-125b in the regulation of keratinocyte proliferation and differentiation, partially through the regulation of FGFR2. Loss of miR-125b in psoriasis skin may contribute to hyperproliferation and aberrant differentiation of keratinocytes.

Epidermal Th22 and Tc17 Cells Form a Localized Disease Memory in Clinically Healed Psoriasis

Psoriasis is a common and chronic inflammatory skin disease in which T cells play a key role. Effective treatment heals the skin without scarring, but typically psoriasis recurs in previously affected areas. A pathogenic memory within the skin has been proposed, but the nature of such site-specific disease memory is unknown. Tissue-resident memory T (TRM) cells have been ascribed a role in immunity after resolved viral skin infections. Because of their localization in the epidermal compartment of the skin, TRM may contribute to tissue pathology during psoriasis. In this study, we investigated whether resolved psoriasis lesions contain TRM cells with the ability to maintain and potentially drive recurrent disease. Three common and effective therapies, narrowband-UVB treatment and long-term biologic treatment systemically inhibiting TNF-α or IL-12/23 signaling were studied. Epidermal T cells were highly activated in psoriasis and a high proportion of CD8 T cells expressed TRM markers. In resolved psoriasis, a population of cutaneous lymphocyte–associated Ag, CCR6, CD103, and IL-23R expressing epidermal CD8 T cells was highly enriched. Epidermal CD8 T cells expressing the TRM marker CD103 responded to ex vivo stimulation with IL-17A production and epidermal CD4 T cells responded with IL-22 production after as long as 6 y of TNF-α inhibition. Our data suggest that epidermal TRM cells are retained in resolved psoriasis and that these cells are capable of producing cytokines with a critical role in psoriasis pathogenesis. We provide a potential mechanism for a site-specific T cell–driven disease memory in psoriasis.

The C-Type Lectin Clec12A Present on Mouse and Human Dendritic Cells Can Serve as a Target for Antigen Delivery and Enhancement of Antibody Responses

We have cloned the mouse and human C-type lectin Clec12A, expressed both, and produced mAb recognizing both. Mouse Clec12A is highly expressed on splenic CD8+ dendritic cells (DC) and plasmacytoid DC. A proportion of CD8−DC also expresses lower levels of Clec12A, as do monocytes, macrophages, and B cells. Human CLEC12A, like the mouse counterpart, is expressed on blood monocytes and DC, including pDC and BDCA-3+DC, the proposed equivalent of mouse CD8+DC. To determine whether Ag targeted to Clec12A could induce immune responses, mice were injected with a rat mAb recognizing Clec12A, or a control rat mAb, then production of anti-rat Ig was measured. Anti-Clec12A mAb alone produced only moderate responses, but these were amplified by coinjecting only small amounts of LPS as a DC activation agent. Furthermore, when OVA was conjugated to anti-Clec12A mAb, OVA-specific T cells were induced to proliferate. This Ag presentation to naive T cells was due to targeting conventional DC, because their ablation eliminated T cell activation. The potent Ab responses induced using microgram amounts of anti-Clec12A and minimal amounts of adjuvant demonstrate that this molecule can be used as an Ag-delivery target to enhance Ab responses to vaccines.

Differential Migration of Epidermal and Dermal Dendritic Cells during Skin Infection

Dendritic cells (DCs) are extremely heterogeneous, most evident in the skin where a variety of different subsets have been identified in recent years. DCs of healthy skin include a number of distinct populations in the dermal layer as well as the well-characterized Langerhans cells (LCs) of the epidermis. These steady-state populations are augmented during bouts of local inflammation by additional monocyte-derived DCs. In an effort to better understand the distinction between the different subsets, we examined their behavior following skin infection with HSV. LC emigration rapidly followed appearance of virus in the skin and resulted in depopulation of regions in areas surrounding infected nerve endings. A separate DC population was found to accumulate within the dermis under patches of active epidermal infection with at least some derived from blood monocyte precursors. Ag-positive DCs could occasionally be found in these dermal accumulations, although they represented a minority of DCs in these areas. In addition, infected DCs appeared compromised in their trafficking capabilities and were largely absent from the migrating population. On resolution of skin disease, LCs repopulated the reformed epidermis and these were of mixed origin, with around half entering from the circulation and the remainder derived from local progenitors. Overall, our results show a range of migrational complexities between distinct skin DC populations as a consequence of localized infection.

Potential Role for IL-7 in Fas-Mediated T Cell Apoptosis During HIV Infection

IL-7 promotes survival of resting T lymphocytes and induces T cell proliferation in lymphopenic conditions. As elevated IL-7 levels occur in HIV-infected individuals in addition to high Fas expression on T cells and increased sensitivity to Fas-induced apoptosis, we analyzed whether IL-7 has a regulatory role in Fas-mediated T cell apoptosis. We show that IL-7 up-regulates Fas expression on naive and memory T cells through a mechanism that involves translocation of Fas molecules from intracellular compartments to the cell membrane. IL-7 induced the association of Fas with the cytoskeletal component ezrin and a polarized Fas expression on the cell surface. The potential role of IL-7 in Fas up-regulation in vivo was verified in IL-7-treated macaques and in HIV-infected or chemotherapy treated patients by the correlation between serum IL-7 levels and Fas expression on T cells. IL-7 treatment primed T cells for Fas-induced apoptosis in vitro and serum IL-7 levels correlated with the sensitivity of T cells to Fas-induced apoptosis in HIV-infected individuals. Our data suggest an important role for IL-7 in Fas-mediated regulation of T cell homeostasis. Elevated IL-7 levels associated with lymphopenic conditions, including HIV-infection, might participate in the increased sensitivity of T cells for activation-induced apoptosis.