Human TH9 cells are skin-tropic and have autocrine and paracrine proinflammatory capacity

Reactive oxygen species in psoriasis and psoriasis arthritis: relevance to human disease

Psoriasis (Ps) is a chronic, immune-mediated, skin inflammatory disease affecting up to 3% of the population worldwide. Different environmental triggers initiate this complex multifactorial syndrome. Many individuals affected by Ps (6-26%) develop inflammatory disease in other organs, often in the joints as in psoriasis arthritis (PsA). Animal models that reflect the typical Ps syndrome, including both skin and joint pathology as in Ps and PsA, are valuable tools for dissecting disease pathways leading to clinical manifestations. In this context, we developed a new acute Ps and PsA-like disease model that appears after exposure to Saccharomyces cerevisiae mannan in certain mouse strains. The disease was found to be triggered by mannan-activated macrophages, leading to the activation of a pathogenic interleukin-17 pathway involving innate lymphocytes. Interestingly, the production of reactive oxygen species protected the mice from the triggering of this pathway and ameliorated Ps and PsA development.

Differentiation, regulation and function of Th9 cells

Naïve CD4(+) T cells are activated and differentiate to distinct lineages of T helper (Th) cells, which are involved in physiological and pathological processes by obtaining the potential to produce different lineage-specific cytokines that mediate adaptive immunity. In the past decade, our knowledge of Th cells has been significantly expanded with the findings of new lineages. Interleukin (IL)-9 producing T cells are recently identified. In consideration of the ability to preferentially secret IL-9, these cells are termed Th9 cells. Given the multiple function of IL-9, Th9 cells participate in the lesion of many diseases, such as allergic inflammation, tumor, and parasitosis. In this chapter, we will focus on the cytokines, co-stimulatory factors, and transcriptional signaling pathways, which regulate Th9 cells development as well as stability, plasticity, and the multiple roles of Th9 cells in vivo.

CD8⁺ T Cell-Independent Immune-Mediated Mechanisms of Anti-Tumor Activity

Despite the growing number of preclinical and clinical trials focused on immunotherapy for the treatment of malignant gliomas, the prognosis for this disease remains grim. Cancer immunotherapy seeks to recruit an effective immune response to eliminate tumor cells. To date, cancer vaccines have shown only limited effectiveness because of our incomplete understanding of the necessary effector cells and mechanisms that yield efficient tumor clearance. CD8+ T cell cytotoxic activity has long been proposed as the primary effector function necessary for tumor regression. However, there is increasing evidence that indicates that components of the immune system other than CD8+ T cells play important roles in tumor eradication and control. The following review should provide an understanding of the mechanisms involved in an effective antitumor response to guide future therapeutic designs. The information provided suggests an alternate means of effective tumor clearance in malignant glioma to the canonical CD8+ cytotoxic T cell mechanism.

Plasticity of human CD4 T cell subsets

Human beings are exposed to a variety of different pathogens, which induce tailored immune responses and consequently generate highly diverse populations of pathogen-specific T cells. CD4(+) T cells have a central role in adaptive immunity, since they provide essential help for both cytotoxic T cell- and antibody-mediated responses. In addition, CD4(+) regulatory T cells are required to maintain self-tolerance and to inhibit immune responses that could damage the host. Initially, two subsets of CD4(+) helper T cells were identified that secrete characteristic effector cytokines and mediate responses against different types of pathogens, i.e., IFN-γ secreting Th1 cells that fight intracellular pathogens, and IL-4 producing Th2 cells that target extracellular parasites. It is now well established that this dichotomy is insufficient to describe the complexity of CD4(+) T cell differentiation, and in particular the human CD4 compartment contains a myriad of T cell subsets with characteristic capacities to produce cytokines and to home to involved tissues. Moreover, it has become increasingly clear that these T cell subsets are not all terminally differentiated cells, but that the majority is plastic and that in particular central memory T cells can acquire different properties and functions in secondary immune responses. In addition, there is compelling evidence that helper T cells can acquire regulatory functions upon chronic stimulation in inflamed tissues. The plasticity of antigen-experienced human T cell subsets is highly relevant for translational medicine, since it opens new perspectives for immune-modulatory therapies for chronic infections, autoimmune diseases, and cancer.

Co-stimulation with TNF receptor superfamily 4/25 antibodies enhances in-vivo expansion of CD4+CD25+Foxp3+ T cells (Tregs) in a mouse study for active DNA Aβ42 immunotherapy

The study was designed to test DNA Aβ42 immunization in mice as alternative approach for possible active immunotherapy in Alzheimer patients. As results, we found polarized Th2 immune responses, efficient Aβ42 antibody levels, and disappearance of antigen specific T cells. In-vivo TNFRSF4/25 antibody co-stimulation enhanced Aβ42 specific T cell responses with initial Th2 expansion and subsequent development of Aβ42 specific CD4+CD25+Foxp3+ cells. It showed that Th2 biased responses due to gene gun immunizations propagate the development of regulatory T cells. In conclusion, full-length DNA Aβ42 immunization into skin results in a regulatory response with minimal risk of inflammation and autoimmunity.

Microbiota control of a tryptophan-AhR pathway in disease tolerance to fungi

An increased understanding of the importance of microbiota in shaping the host's immune and metabolic activities has rendered fungal interactions with their hosts more complex than previously appreciated. The aryl hydrocarbon receptor (AhR) has a pivotal role in connecting tryptophan catabolism by microbial communities and the host's own pathway of tryptophan metabolite production with the orchestration of T-cell function. AhR activation by a Lactobacillus-derived AhR ligand leads to the production of IL-22 to the benefit of mucosal defense mechanisms, an activity upregulated in the absence of the host tryptophan catabolic enzyme, indoleamine 2,3-dioxygenase 1 (IDO1), which is required for protection from fungal diseases ("disease tolerance"). As AhR activation in turn leads to the activation-in a feedback fashion-of IDO1, the regulatory loop involving AhR and IDO1 may have driven the coevolution of commensal fungi with the mammalian immune system and the microbiota, to the benefit of host survival and fungal commensalism. This review will discuss the essential help the microbiota provides in controlling the balance between the dual nature of the fungal-host relationship, namely, commensalism vs. infection.

Antifungal Th Immunity: Growing up in Family

Fungal diseases represent an important paradigm in immunology since they can result from either the lack of recognition or over-activation of the inflammatory response. Current understanding of the pathophysiology underlying fungal infections and diseases highlights the multiple cell populations and cell-signaling pathways involved in these conditions. A systems biology approach that integrates investigations of immunity at the systems-level is required to generate novel insights into this complexity and to decipher the dynamics of the host–fungus interaction. It is becoming clear that a three-way interaction between the host, microbiota, and fungi dictates the types of host–fungus relationship. Tryptophan metabolism helps support this interaction, being exploited by the mammalian host and commensals to increase fitness in response to fungi via resistance and tolerance mechanisms of antifungal immunity. The cellular and molecular mechanisms that provide immune homeostasis with the fungal biota and its possible rupture in fungal infections and diseases will be discussed within the expanding role of antifungal Th cell responses.

The panoply of αβT cells in the skin

Skin protects body from continual attack by microbial pathogens and environmental factors. Such barrier function of skin is achieved by multiple components including immune system, which is mainly regulated by lymphocytes. T lymphocytes (T cells) that express T cell receptor (TCR) α and β chains (αβT cells) control the strength and the type of immune response. CD4T cell population consists of helper T (Th) cell-subsets and immunosuppressive regulatory T (Treg) cells. Th1 cells produce IFN-γ and protect against intracellular pathogens. Th2 cells produce IL-4 family cytokines and participate in allergic skin diseases, including atopic dermatitis (AD). Th17 cells secrete IL-17, recruit granulocytes to fight against extracellular microorganisms, and play a role in psoriasis and AD. Th22 cells produce IL-22 that activates epithelial cells and mediates acanthosis in psoriasis and AD. On the other hand, Foxp3+ Treg cells attenuate immune responses partly via TGF-β or IL-10. Tissue resident memory T (Trm) cells in the skin-most of which are epidermal CD8T cells-constitute the first line of the defense against repeated infections. CD8 T cells are also engaged in psoriasis, lichen planus, and drug eruptions. Skin harbors innate-like αβT cells such as natural killer T (NKT) cells as well, whose function is not fully revealed. Understanding these αβT cells helps to comprehend skin diseases.