Roles of lymphoid cells in the differentiation of Langerhans dendritic cells in mice

Human genetic dissection of papillomavirus-driven diseases: new insight into their pathogenesis

Human papillomaviruses (HPVs) infect mucosal or cutaneous stratified epithelia. There are 5 genera and more than 200 types of HPV, each with a specific tropism and virulence. HPV infections are typically asymptomatic or result in benign tumors, which may be disseminated or persistent in rare cases, but a few oncogenic HPVs can cause cancers. This review deals with the human genetic and immunological basis of interindividual clinical variability in the course of HPV infections of the skin and mucosae. Typical epidermodysplasia verruciformis (EV) is characterized by β-HPV-driven flat wart-like and pityriasis-like cutaneous lesions and non-melanoma skin cancers in patients with inborn errors of EVER1-EVER2-CIB1-dependent skin-intrinsic immunity. Atypical EV is associated with other infectious diseases in patients with inborn errors of T cells. Severe cutaneous or anogenital warts, including anogenital cancers, are also driven by certain α-, γ-, μ or ν-HPVs in patients with inborn errors of T lymphocytes and antigen-presenting cells. The genetic basis of HPV diseases at other mucosal sites, such as oral multifocal epithelial hyperplasia or juvenile recurrent respiratory papillomatosis (JRRP), remains poorly understood. The human genetic dissection of HPV-driven lesions will clarify the molecular and cellular basis of protective immunity to HPVs, and should lead to novel diagnostic, preventive, and curative approaches in patients.

Dendritic cell-expressed common gamma-chain recruits IL-15 for trans-presentation at the murine immunological synapse

Background: Mutations of the common cytokine receptor gamma chain (γc) cause Severe Combined Immunodeficiency characterized by absent T and NK cell development. Although stem cell therapy restores these lineages, residual immune defects are observed that may result from selective persistence of γc-deficiency in myeloid lineages. However, little is known about the contribution of myeloid-expressed γc to protective immune responses.  Here we examine the importance of γc for myeloid dendritic cell (DC) function. Methods: We utilize a combination of in vitro DC/T-cell co-culture assays and a novel lipid bilayer system mimicking the T cell surface to delineate the role of DC-expressed γc during DC/T-cell interaction. Results: We observed that γc in DC was recruited to the contact interface following MHCII ligation, and promoted IL-15Rα colocalization with engaged MHCII. Unexpectedly, trans-presentation of IL-15 was required for optimal CD4+T cell activation by DC and depended on DC γc expression. Neither recruitment of IL-15Rα nor IL-15 trans-signaling at the DC immune synapse (IS), required γc signaling in DC, suggesting that γc facilitates IL-15 transpresentation through induced intermolecular cis associations or cytoskeletal reorganization following MHCII ligation. Conclusions: These findings show that DC-expressed γc is required for effective antigen-induced CD4+ T cell activation. We reveal a novel mechanism for recruitment of DC IL-15/IL-15Rα complexes to the IS, leading to CD4+ T cell costimulation through localized IL-15 transpresentation that is coordinated with antigen-recognition.

Langerhans cells are not required for epidermal Vgamma3 T cell homeostasis and function

This study tested the hypothesis that Vγ3 TCR-bearing T cells are influenced by LCs. Vγ3 T cells and LCs are located in the epidermis of mice. Vγ3 T cells represent the main T cell population in the skin epithelium and play a crucial role in maintaining the skin integrity, whereas LCs are professional APCs. Although Vγ3 T cells and LCs form an interdigitating network in the epidermis, not much is known about their reciprocal influence and/or interdependence. We used two different LC-deficient mouse models, in which LCs are constitutively or inducibly depleted, to investigate the role of LCs in maturation, homeostasis, and function of Vγ3 T cells. We show that Vγ3 T cell numbers are unaltered by LC deficiency, and Vγ3 T cells isolated from LC-deficient mice are phenotypically and upon in vitro stimulation, functionally indistinguishable from Vγ3 T cells isolated from WT mice based on their cytotoxic potential and cytokine production. Additionally, in vivo skin-wounding experiments show no major difference in response of Vγ3 T cells to wounding in the absence or presence of LCs. These observations indicate that Vγ3 T cells develop and function independently of LCs.

Langerhans cell (LC) proliferation mediates neonatal development, homeostasis, and inflammation-associated expansion of the epidermal LC network

Most tissues develop from stem cells and precursors that undergo differentiation as their proliferative potential decreases. Mature differentiated cells rarely proliferate and are replaced at the end of their life by new cells derived from precursors. Langerhans cells (LCs) of the epidermis, although of myeloid origin, were shown to renew in tissues independently from the bone marrow, suggesting the existence of a dermal or epidermal progenitor. We investigated the mechanisms involved in LC development and homeostasis. We observed that a single wave of LC precursors was recruited in the epidermis of mice around embryonic day 18 and acquired a dendritic morphology, major histocompatibility complex II, CD11c, and langerin expression immediately after birth. Langerin⁺ cells then undergo a massive burst of proliferation between postnatal day 2 (P2) and P7, expanding their numbers by 10–20-fold. After the first week of life, we observed low-level proliferation of langerin⁺ cells within the epidermis. However, in a mouse model of atopic dermatitis (AD), a keratinocyte signal triggered increased epidermal LC proliferation. Similar findings were observed in epidermis from human patients with AD. Therefore, proliferation of differentiated resident cells represents an alternative pathway for development in the newborn, homeostasis, and expansion in adults of selected myeloid cell populations such as LCs. This mechanism may be relevant in locations where leukocyte trafficking is limited.

IL-21 administration into the nostril alleviates murine allergic rhinitis

Type I allergic diseases such as allergic rhinitis are caused by IgE-mediated humoral immune responses, while eosinophils also fulfill important roles in the etiology of IgE-mediated allergy. IL-21 regulates growth, differentiation, and function of T, B, and NK cells, while the production of IgE is also influenced by IL-21. In this study we examined whether IL-21 is capable of controlling IgE-mediated allergic reactions in vivo by using the allergic rhinitis mouse model that was established by repetitive sensitization and intranasal challenge with OVA. Intranasal administration with recombinant mouse IL-21 (rmIL-21) significantly reduced the number of sneezes, as well as the serum concentration of OVA-specific IgE, in comparison with that of untreated allergic mice. The rmIL-21 treatment also suppressed germline Cepsilon transcription in the nasal-associated lymphoid tissues, which may have, at least partly, resulted from the up-regulation of Bcl-6 mRNA caused by IL-21. Local expression of IL-4, IL-5, and IL-13 was also inhibited by the intranasal cytokine therapy whereas, in contrast, the expression of endogenous IL-21 mRNA was induced by exogenous rmIL-21. Moreover, IL-21 acted on nasal fibroblasts to inhibit production of eotaxin. This novel function of IL-21 may be associated with the attenuation of eosinophil infiltration into nasal mucosa that was revealed by histopathological observation. These results indicated that IL-21 nasal administration effectively ameliorated allergic rhinitis through pleiotropic activities, i.e., the prevention of IgE production by B cells and eotaxin production by fibroblasts.

Dendritic-cell trafficking to lymph nodes through lymphatic vessels

Antigen-presenting dendritic cells often acquire foreign antigens in peripheral tissues such as the skin. Optimal encounter with naive T cells for the presentation of these antigens requires that the dendritic cells migrate to draining lymph nodes through lymphatic vessels. In this article, we review important aspects of what is known about dendritic-cell trafficking into and through lymphatic vessels to lymph nodes. We present these findings in the context of information about lymphatic-vessel biology. Gaining a better understanding of the crosstalk between dendritic cells and lymphatic vessels during the migration of dendritic cells to lymph nodes is essential for future advances in manipulating dendritic-cell migration as a means to fine-tune immune responses in clinical settings.