Tumour necrosis factor receptor II (p75) signalling is required for the migration of Langerhans' cells

TNF-α and IL-1β Do Not Induce Langerhans Cell Migration by Inhibiting TGFβ Activation

In the skin, Langerhans cells (LCs) require autocrine latent TGFβ that is transactivated by the integrins ανβ6 and ανβ8 expressed by keratinocytes (KCs) for long-term epidermal retention. Selective expression of a ligand-independent, constitutively active form of TGFβR1 inhibits LC migration during homeostasis and in response to UVB exposure. In this study, we found that LC migration in response to inflammatory stimuli was also inhibited by ligand-independent TGFβR1 signaling. Contrary to UVB stimulation, which reduced KC expression of ανβ6, in vitro and in vivo exposure to TNF-α or IL-1β increased ανβ6 transcript and protein expression by KCs. This resulted in increased KC-mediated transactivation of latent TGFβ. Expression of ανβ8 was largely unchanged. These findings show that ligand-independent TGFβR1 signaling in LCs can overcome inflammatory migration stimuli, but reduced KC-mediated transactivation of latent TGFβ by KCs may only drive LC migration during homeostasis and in response to UV stimulation.

The Dynamics of the Skin's Immune System

The skin is a complex organ that has devised numerous strategies, such as physical, chemical, and microbiological barriers, to protect the host from external insults. In addition, the skin contains an intricate network of immune cells resident to the tissue, crucial for host defense as well as tissue homeostasis. In the event of an insult, the skin-resident immune cells are crucial not only for prevention of infection but also for tissue reconstruction. Deregulation of immune responses often leads to impaired healing and poor tissue restoration and function. In this review, we will discuss the defensive components of the skin and focus on the function of skin-resident immune cells in homeostasis and their role in wound healing.

Ontogeny and function of murine epidermal Langerhans cells

Langerhans cells (LCs) are epidermis-resident antigen-presenting cells that share a common ontogeny with macrophages but function as dendritic cells (DCs). Their development, recruitment and retention in the epidermis is orchestrated by interactions with keratinocytes through multiple mechanisms. LC and dermal DC subsets often show functional redundancy, but LCs are required for specific types of adaptive immune responses when antigen is concentrated in the epidermis. This Review will focus on those developmental and functional properties that are unique to LCs.

Immunosuppressive effects of Amblyomma cajennense tick saliva on murine bone marrow-derived dendritic cells

Background

Dendritic cells (DCs) are professional antigen-presenting cells with vital roles in the activation of host immunity. Ticks are bloodsucking arthropods that secrete bioactive compounds with immunomodulatory properties via their saliva. It is known that some tick species modulate the biology of DCs with different intensities; however, studies on Amblyomma cajennense, the Cayenne tick, have not yet been performed, although this species is considered one of the most capable of modulating immune responses of different hosts.

Methods

Engorged female ticks were stimulated with dopamine to induce salivation, and saliva was pooled. The effects of tick saliva on the biology of dendritic cells were assessed by examining DC differentiation, maturation, migration, cellular viability, cytokine production and expression of surface markers by flow cytometry and ELISA. Competitive enzyme immunoassays (EIA) were used to measure saliva prostaglandin-E₂ (PGE₂). Statistical significance was determined by ANOVA followed by Tukey’s post-test or by the Kruskal-Wallis test with the Dunns post-test.

Results

In this work, we demonstrated that the presence of A. cajennense saliva to bone marrow cultures inhibit DC differentiation. This inhibition was not accompanied by inhibition or induction of stimulatory and co-stimulatory molecules such as MHC-II, CD40, CD80 or CD86. Immature and mature DCs that were pre-exposed to saliva showed reduced migration toward the chemokines RANTES and MIP-3β. This inhibition was associated to a reduced expression of CCR5 (the receptor for RANTES) or CCR7 (the receptor for MIP-3β) induced by the presence of saliva in the cultures. Tick saliva also inhibited IL-12p40, IL-6 and TNF-α in a concentration-dependent manner while potentiating IL-10 cytokine production by DCs stimulated with Toll-like receptor-4 ligand. Additionally, A. cajennense tick saliva inhibited the expression of CD40 and CD86 in mature DCs while potentiating the expression of PD-L1. PGE₂ was detected as one of the constituents of saliva at a concentration of ~ 80 ng/ml, and we believe that most of the results reported herein are due to the presence of PGE₂.

Conclusions

These results help to understand the tick-host interaction and demonstrate that A. cajennense ticks appear to have mechanisms for modulating host immune cells, including DCs.

Impaired Contact Hypersensitivity Reaction and Reduced Production of Vascular Endothelial Growth Factor in Tumor Necrosis Factor-α Gene-Deficient Mice

Tumor necrosis factor (TNF)-alpha is an important proinflammatory cytokine in contact hypersensitivity (CHS) reactions. Previous efforts to assay CHS in TNF-alpha gene-deficient (-/-) mice have demonstrated a significant reduction in ear skin weight at 24 h following challenge by oxazolone, although the mechanisms of this suppression have not been examined. To further characterize the impaired CHS during evolution of the elicitation phase in TNF-alpha -/- mice and to clarify its mechanisms, focusing on the roles of TNF-alpha and vascular endothelial growth factor (VEGF), we used an established method of CHS assay-sensitization and challenge by trinitrochlorobenzene (TNCB)- in TNF-alpha -/- and wild-type mice. We compared the histopathology of the sequential evolution of CHS between the two groups of mice and assessed both the extent of inflammatory cell infiltration and the degree of dilatation in dermal vessels labeled with CD31. We quantified the production of VEGF in the epidermis at specific time points by using a murine VEGF ELISA kit. The CHS reaction was markedly suppressed in TNF-alpha -/- mice at all time points of the elicitation phase. Histologically, in TNF-alpha -/- mice we observed diminished vascular permeability, reduced numbers of infiltrating inflammatory cells, neutrophils at 12 h, mononuclear cells and eosinophils at 24 h, and a decreased area of dilatation of vessels labeled with CD31. The level of epidermal VEGF in wild type mice increased rapidly after challenge and peaked at 24 h, paralleling the peak of ear swelling. In contrast, the peak level of epidermal VEGF in TNF-alpha -/- mice was significantly reduced. These results suggest that TNF-alpha plays an enhancing role in the elicitation phase of the CHS reaction. Diminished degrees of vascular permeability, dilatation of CD31+ vessels, and inflammatory cell infiltration in TNF-alpha -/- mice are likely to be the result of a lack of TNF-alpha and reduced production of epidermal VEGF.

TNF-α is involved in the abnormal thymocyte migration during experimental Trypanosoma cruzi infection and favors the export of immature cells

Previous studies revealed a significant production of inflammatory cytokines together with severe thymic atrophy and thymocyte migratory disturbances during experimental Chagas disease. Migratory activity of thymocytes and mature T cells seem to be finely tuned by cytokines, chemokines and extracellular matrix (ECM) components. Systemic TNF-α is enhanced during infection and appears to be crucial in the response against the parasite. However, it also seems to be involved in disease pathology, since it is implicated in the arrival of T cells to effector sites, including the myocardium. Herein, we analyzed the role of TNF-α in the migratory activity of thymocytes in Trypanosoma cruzi (T. cruzi) acutely-infected mice. We found increased expression and deposition of TNF-α in the thymus of infected animals compared to controls, accompanied by increased co-localization of fibronectin, a cell migration-related ECM molecule, whose contents in the thymus of infected mice is also augmented. In-vivo studies showed an enhanced export of thymocytes in T. cruzi-infected mice, as ascertained by intrathymic injection of FITC alone or in combination with TNF-α. The increase of immature CD4⁺CD8⁺ T cells in secondary lymphoid organs was even more clear-cut when TNF-α was co-injected with FITC. Ex-vivo transmigration assays also revealed higher number of migrating cells when TNF-α was added onto fibronectin lattices, with higher input of all thymocyte subsets, including immature CD4⁺CD8⁺. Infected animals also exhibit enhanced levels of expression of both mRNA TNF-α receptors in the CD4⁺CD8⁺ subpopulation. Our findings suggest that in T. cruzi acute infection, when TNF-α is complexed with fibronectin, it favours the altered migration of thymocytes, promoting the release of mature and immature T cells to different compartments of the immune system. Conceptually, this work reinforces the notion that thymocyte migration is a multivectorial biological event in health and disease, and that TNF-α is a further player in the process.

Disruption of TNF-α/TNFR1 function in resident skin cells impairs host immune response against cutaneous vaccinia virus infection

One strategy adopted by vaccinia virus (VV) to evade the host immune system is to encode homologs of TNF receptors (TNFRs) that block TNF-α function. The response to VV skin infection under conditions of TNF-α deficiency, however, has not been reported. We found that TNFR1-/- mice developed larger primary lesions, numerous satellite lesions, and higher skin virus levels after VV scarification. Following their recovery, VV-scarified TNFR1-/- mice were fully protected against challenge with a lethal intranasal dose of VV, suggesting these mice had developed an effective memory immune response. A functional systemic immune response was further demonstrated by enhanced production of VV-specific IFN-γ and VV-specific CD8(+) T cells in spleens and draining lymph nodes. Interestingly, bone marrow (BM)-reconstitution studies using wild-type (WT) BM in TNFR1-/- host mice, but not TNFR1-/- BM in WT host mice, reproduced the original results seen in TNFR1-/- mice, indicating that TNFR1 deficiency in resident skin cells, rather than hematopoietic cells, accounts for the impaired cutaneous immune response. Our data suggest that lack of TNFR1 leads to a skin-specific immune deficiency, and that resident skin cells have a crucial role in mediating an optimal immune defense to VV cutaneous infection via TNF-α/TNFR1 signaling.

Phospho-SXXE/D motif mediated TNF receptor 1-TRADD death domain complex formation for T cell activation and migration

In TNF-treated cells, TNFR1, TNFR-associated death domain protein (TRADD), Fas-associated death domain protein, and receptor-interacting protein kinase proteins form the signaling complex via modular interaction within their C-terminal death domains. In this paper, we report that the death domain SXXE/D motifs (i.e., S381DHE motif of TNFR1-death domain as well as S215LKD and S296LAE motifs of TRADD-death domain) are phosphorylated, and this is required for stable TNFR1-TRADD complex formation and subsequent activation of NF-κB. Phospho-S215LKD and phospho-S296LAE motifs are also critical to TRADD for recruiting Fas-associated death domain protein and receptor-interacting protein kinase. IκB kinase β plays a critical role in TNFR1 phosphorylation of S381, which leads to subsequent T cell migration and accumulation. Consistently, we observed in inflammatory bowel disease specimens that TNFR1 was constitutively phosphorylated on S381 in those inflammatory T cells, which had accumulated in high numbers in the inflamed mucosa. Therefore, SXXE/D motifs found in the cytoplasmic domains of many TNFR family members and their adaptor proteins may serve to function as a specific interaction module for the α-helical death domain signal transduction.

Imunopatologia da dermatite de contato alérgica

A dermatite de contato alérgica é consequência de uma reação imune mediada por células T contra químicos de baixo peso molecular, denominados haptenos. É uma condição frequente que ocorre em todas as raças e faixas etárias e afeta a qualidade de vida de seus portadores. O mecanismo imunológico desta doença vem sendo revisto nas últimas décadas com significativo avanço no seu entendimento. A metabolização e o caminho dos haptenos, bem como a formação e o mecanismo de ação das células responsáveis tanto pela reação quanto pelo seu término, são discutidos neste artigo

Dendritic cells and skin sensitization: Biological roles and uses in hazard identification

Recent advances have been made in our understanding of the roles played by cutaneous dendritic cells (DCs) in the induction of contact allergy. A number of associated changes in epidermal Langerhans cell phenotype and function required for effective skin sensitization are providing the foundations for the development of cellular assays (using DC and DC-like cells) for skin sensitization hazard identification. These alternative approaches to the identification and characterization of skin sensitizing chemicals were the focus of a Workshop entitled "Dendritic Cells and Skin Sensitization: Biological Roles and Uses in Hazard Identification" that was given at the annual Society of Toxicology meeting held March 6-9, 2006 in San Diego, California. This paper reports information that was presented during the Workshop.

Inflammation, lymphatic function, and dendritic cell migration

The lymphatic system is not only essential for maintenance of normal fluid balance, but also for proper immunologic function by providing an extensive network of vessels, important for cell trafficking and antigen delivery, as well as an exclusive environment, the lymph node (LN), where antigen-presenting cells (APCs) and lymphocytes can encounter and interact. Among APCs, dendritic cells (DCs) have a remarkable capacity to traffic from peripheral tissues to the draining LN, which is critical for execution of their functions. To reach the LN, DCs must migrate towards and enter lymphatic vessels. Here, the authors review what is known about the factors that drive this process. They touch particularly on the topic of how DC migration is affected by inflammation and discuss this in the context of lymphatic function. Traditionally, inflammatory mediators are regarded to support DC migration to LNs because they induce molecules on DCs known to guide them to lymphatics. The authors recently showed that inflammatory signals present in a strong vaccine adjuvant induce swelling in LNs accompanied by lymphangiogenesis in the draining LN and radius of peripheral tissue. These increased lymphatics, at least for several days, lead to a more robust migration of DCs. However, the density of lymphatic vessels can become overly extended and/or their function impaired as observed during lymphedema and various chronic inflammatory reactions. Diseases characterized by chronic inflammation often present with impaired DC migration and adaptive immunity. Gaining a better understanding of how lymphatic vessel function may impact adaptive immunity by, for example, altering DC migration will benefit clinical research aiming to manipulate immune responses and manage chronic inflammatory diseases.

EC-SOD suppresses contact hypersensitivity in mouse skin by impairing Langerhans cell migration

Extracellular superoxide dismutase (EC-SOD) is primarily a tissue enzyme and has been implicated in the modulation of inflammatory response. The biological role of EC-SOD in skin, however, has rarely been investigated. In this study, we aim to explore the effects of EC-SOD on the inflammatory response in skin by evaluating the contact hypersensitivity response (CHS) in EC-SOD transgenic mice. Transgenic mice with skin-specific expression of EC-SOD were sensitized and challenged with 2,4,6-trinitro-1-chlorobenzene (TNCB), followed by measurement of ear swelling. EC-SOD transgenic mice showed significantly reduced CHS responses compared with wild-type mice. Histological evaluation of the challenged ears of EC-SOD transgenic mice revealed diminished infiltration of inflammatory cells with a failure to induce expression of inflammatory cytokines, such as tumor necrosis factor-alpha and IFN-gamma, on sensitization and challenge with TNCB. Furthermore, Langerhans cell migration to lymph nodes was impaired in EC-SOD transgenic mice. These results indicate that EC-SOD downregulates CHS through inhibition of the inflammatory response, suggesting a possible therapeutic regimen in inflammatory skin diseases.

Biology of Langerhans cells and Langerhans cell histiocytosis

Langerhans cells (LC) are epidermal dendritic cells (DC). They play an important role in the initiation of immune responses through antigen uptake, processing, and presentation to T cells. Langerhans cell histiocytosis (LCH) is a rare disease in which accumulation of cells with LC characteristics (LCH cells) occur. LCH lesions are further characterized by the presence of other cell types, such as T cells, multinucleated giant cells (MGC), macrophages (MPhi), eosinophils, stromal cells, and natural killer cells (NK cells). Much has been learned about the pathophysiology of LCH by studying properties of these different cells and their interaction with each other through cytokines/chemokines. In this review we discuss the properties and interactions of the different cells involved in LCH pathophysiology with the hope of better understanding this enigmatic disorder.

Cytokines and Langerhans cell mobilisation in mouse and man

A critical event during the development of cutaneous immune responses, including those provoked by contact allergens, is the mobilisation of epidermal Langerhans cells (LC). These cells act as sentinels of the immune system in the skin, responding to a variety of local insults with migration and delivery of potentially foreign signals to draining lymph nodes. Experimental studies have revealed that the regulation of mobilisation and migration of LC display striking similarities in man and mouse. In both species it has been found that the successful induction of migration requires that LC receive (at least) 2 independent cytokine signals; provided by tumour necrosis factor-alpha (TNF-alpha) and interleukin 1beta. In addition, a similar heterogeneity in man and mouse is apparent with regard to the fraction of LC responding rapidly to mobilisation signals, with the same proportion of cells (20%-30%) being stimulated to migrate in each case. Other similarities exist between mice and humans with respect to LC function, including an age-related decrement in both LC frequency and responsiveness to TNF-alpha. Collectively these studies demonstrate that the mouse provides a valuable experimental surrogate for the human skin immune system, particularly with respect to LC biology, and suggest that it is possible to perform extrapolations between species with some confidence.

Prolonged production of TNF-alpha exacerbates illness during respiratory syncytial virus infection

CD8(+) CTL are the main effector cells responsible for resolving viral infections. However, the CTL response to respiratory syncytial virus (RSV) infection in mice facilitates viral clearance at the expense of significant immunopathology. Previous reports have shown a strong correlation between the mechanism of CTL activity and the severity of RSV-induced illness. Furthermore, experiments in perforin knockout mice revealed that antiviral cytokine production temporally correlated with RSV-induced illness. In the current study, we show that TNF-alpha is the dominant mediator of RSV-associated illness, and it is also important for clearance of virus-infected cells during the early stages of infection. We also demonstrate that IFN-gamma plays a protective role in conjunction with perforin/granzyme-mediated killing. Preliminary experiments in gld mice that express nonfunctional Fas ligand (FasL) revealed that RSV-induced illness is significantly reduced in the absence of FasL-mediated killing. Antiviral cytokine production was not elevated in the absence of FasL, suggesting a possible link between FasL and antiviral cytokine activity. This work shows that multiple phenotypic subsets of CD8(+) CTLs respond to RSV infection, each with varying capacities for clearance of virus-infected cells and the induction of illness. In addition, the revelation that TNF-alpha is the principal mediator of RSV-induced illness means that administration of TNF receptor antagonists, in combination with antiviral therapy, may be an effective method to treat RSV infections.

Impaired lymphoid chemokine-mediated migration due to a block on the chemokine receptor switch in human cytomegalovirus-infected dendritic cells

Dendritic cell (DC) migration from the site of infection to the site of T-cell priming is a crucial event in the generation of antiviral T-cell responses. Here we present to our knowledge the first functional evidence that human cytomegalovirus (HCMV) blocks the migration of infected monocyte-derived DCs toward lymphoid chemokines CCL19 and CCL21. DC migration is blocked by viral impairment of the chemokine receptor switch at the level of the expression of CCR7 molecules. The inhibition occurs with immediate-early-early kinetics, and viral interference with NF-kappaB signaling is likely to be at least partially responsible for the lack of CCR7 expression. DCs which migrate from the infected cultures are HCMV antigen negative, and consequently they do not stimulate HCMV-specific CD8(+) T cells, while CD4(+)-T-cell activation is not impaired. Although CD8(+) T cells can also be activated by alternative antigen presentation mechanisms, the spatial segregation of naive T cells and infected DCs seems a potent mechanism of delaying the generation of primary CD8(+)-T-cell responses and aiding early viral spread.

Extracts of scabies mites (Sarcoptidae: Sarcoptes scabiei) modulate cytokine expression by human peripheral blood mononuclear cells and dendritic cells

We performed a series of experiments to determine if human peripheral blood mononuclear cells (PBMCs) from a healthy donor and dendritic cells (NHDCs) derived from these PBMCs reacted to molecules in a scabies extract. PBMCs extravasate from the circulatory system and enter tissues such as scabietic lesions, where monocytes become macrophages. Cells were cultured in medium alone or medium containing 50 microg/ml of Sarcoptes scabiei (SS) extract, 50 ng/ml E. coli lipopolysaccharide (LPS), or SS + LPS together. Supernatants were collected and assayed by enzyme-linked immunosorbent assay (ELISA) for specific cytokines. PBMCs stimulated with SS or LPS exhibited moderately upregulated production of interleukin (IL)-1beta and huge increases in secretions of IL-6, IL-8 and TNF-alpha. Cells co-stimulated with both SS and LPS generally secreted more of these cytokines than cells stimulated with either SS or LPS alone. LPS induced a small amount of IL-1alpha secretion, whereas SS did not, and neither additive resulted in the production of IL-10. NHDCs did not produce IL-1alpha, IL-1beta, IL-6, IL-8, or IL-10 in response to stimulation with SS. These cells did produce IL-6, IL-8, and tumor necrosis factor (TNF)-alpha in response to LPS. When cells were co-stimulated with both LPS and SS, the production of IL-6 and IL-8 was significantly reduced compared with the levels secreted after LPS stimulation alone. These studies show that molecules in a whole body extract of S. scabiei modulate the function of PBMCs (probably monocytes) and dendritic cells.

Depletion of Langerhans cells in human papillomavirus type 16-infected skin is associated with E6-mediated down regulation of E-cadherin

Human papillomavirus type 16 (HPV16) is an oncogenic virus that causes persistent infections in cervical epithelium. The chronic nature of HPV16 infections suggests that this virus actively evades the host immune response. Intraepithelial Langerhans cells (LC) are antigen-presenting cells that are critical in T-cell priming in response to viral infections of the skin. Here we show that HPV16 infection is directly associated with a reduction in the numbers of LC in infected epidermis. Adhesion between keratinocytes (KC) and LC, mediated by E-cadherin, is important in the retention of LC in the skin. Cell surface E-cadherin is reduced on HPV16-infected basal KC, and this is directly associated with the reduction in numbers of LC in infected epidermis. Expression of a single viral early protein, HPV16 E6, in KC reduces levels of cell surface E-cadherin thereby interfering with E-cadherin-mediated adhesion. Through this pathway, E6 expression in HPV16-infected KC may limit presentation of viral antigens by LC to the immune system, thus preventing the initiation of a cell-mediated immune response and promoting survival of the virus.

Epidermal Langerhans cell migration and sensitisation to chemical allergens

Epidermal Langerhans cells (LC) form part of the wider family of dendritic cells (DC; professional antigen-processing and antigen-presenting cells). LC are considered to serve in the skin as sentinels of the adaptive immune system, surveying the local environment and transporting foreign antigen for presentation to responsive T lymphocytes in regional lymph nodes. As such, LC play pivotal roles in the initiation of cutaneous immune responses, including immune responses to chemical allergens encountered at skin surfaces. Here we explore two aspects of LC function in the context of sensitisation to chemical allergens. The first is consideration of the cytokine and chemokine signals that regulate and counter-regulate the mobilisation and migration of LC from the epidermis to skin-draining lymph nodes following topical sensitisation. The second is examination of the ways in which LC may influence the polarity of induced T lymphocytes, and thereby the quality of immune responses.

Differential regulation of sensitizer-induced inflammation and immunity by acute restraint stress in allergic contact dermatitis

Previously, we demonstrated that restraint stress applied before chemical sensitization modulates allergic contact dermatitis (ACD) differently than restraint applied before challenge. In this study, we asked if these dichotomous restraint-induced changes reflect modulation of the cutaneous microenvironment or changes in development of antigen-specific immunity in the lymph node (LN) of BALB/c mice. Our data confirm that restraint suppresses T cell-dependent immunity in ACD when applied prior to sensitization or prior to challenge and demonstrate that the stress-induced increase in ear swelling is due to heightened inflammation associated with ACD and is dependent upon the sensitization status of the mouse.

NF-kappa B hyperactivation has differential effects on the APC function of nonobese diabetic mouse macrophages

Type 1 diabetes is characterized by a chronic inflammatory response resulting in the selective destruction of the insulin-producing beta cells. We have previously demonstrated that dendritic cells (DCs) prepared from nonobese diabetic (NOD) mice, a model for spontaneous type 1 diabetes, exhibit hyperactivation of NF-kappaB resulting in an increased capacity to secrete proinflammatory cytokines and stimulate T cells compared with DCs of nondiabetic strains of mice. In the current study, the activational status of NF-kappaB and its role in regulating the APC function of macrophages (Mphi) prepared from NOD, nonobese resistant (NOR), and BALB/c mice was investigated. Independent of the stimulus, splenic and bone marrow-derived Mphi prepared from NOD mice exhibited increased NF-kappaB activation relative to NOR and BALB/c Mphi. This hyperactivation was detected for different NF-kappaB complexes and correlated with increased IkappaBalpha degradation. Furthermore, increased NF-kappaB activation resulted in an enhanced capacity of NOD vs NOR or BALB/c Mphi to secrete IL-12(p70), TNF-alpha, and IL-1alpha, which was inhibited upon infection with an adenoviral recombinant encoding a modified form of IkappaBalpha. In contrast, elevated NF-kappaB activation had no significant effect on the capacity of NOD Mphi to stimulate CD4(+) or CD8(+) T cells in an Ag-specific manner. These results demonstrate that in addition to NOD DCs, NOD Mphi exhibit hyperactivation of NF-kappaB, which correlates with an increased ability to mediate a proinflammatory response. Furthermore, NF-kappaB influences Mphi APC function by regulating cytokine secretion but not T cell stimulation.

Linomide inhibits insulitis and modulates cytokine production in pancreatic islets in the nonobese diabetic mouse

Linomide is an immunomodulator which has been shown to potently inhibit autoimmunity in several animal models for human autoimmune diseases, including type I diabetes in the nonobese diabetic (NOD) mouse. In this study, we investigate the basis for Linomide's protective effects in the NOD mouse by immunohistochemical and RT-PCR analysis of the phenotype and cytokine expression by cells infiltrating the islets of Langerhans in the pancreas. Linomide treatment was found to reduce the infiltration of T cells, B cells, dendritic cells (DC) and MHC class II(+) cells into the islets, but did not reduce macrophage (MPhi) infiltration. This was seen following Linomide treatment at 3-5, 4-8 and 14-24 weeks of age and thus appears to be independent of the stage of the autoreactive process and the extent of insulitis. The reduced insulitis may be due to reduced expression of adhesion molecules since decreased numbers of islet-associated blood vessels expressing CD106 and MAdCAM-1 were detected following Linomide treatment. Furthermore, short term Linomide treatment (3 or 7 days), which did not alter the number of infiltrating cells, was found to inhibit the production of TNF-alpha which is known to induce the expression of CD106 and MAdCAM-1. These results suggest that the reduced insulitis observed in Linomide-treated animals is secondary to a functional modulation of infiltrating cells.

Lactoferrin: influences on Langerhans cells, epidermal cytokines, and cutaneous inflammation

It has been suggested previously that, in addition to other biological roles, lactoferrin (LF) may display antiinflammatory properties secondary to the regulation of cytokine expression. To explore this concept further, we have here examined in human volunteers the influence of recombinant homologous LF on the migration of epidermal Langerhans cells (LC), a process that is known to be dependent upon the local availability of certain proinflammatory cytokines including tumor necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta). In common with previous studies in mice, it was found that topical administration of LF prior to exposure at the same site to the contact sensitizer diphenylcyclopropenone resulted in a significant reduction of allergen-induced LC migration from the epidermis (measured as a function of the frequency of CD1a+ or HLA-DR+ LC found in epidermal sheets prepared from punch biopsies of the treated skin sites). However, under the same conditions of exposure, LF was unable to influence migration of LC induced by the intradermal administration of TNF-alpha data consistent with the hypothesis that one action of LF in the skin is to regulate the local production of this cytokine. Further support for this hypothesis was derived from experiments conducted with IL-1beta. This cytokine is also able to induce the mobilization of LC following intradermal injection, although in this case, migration is known to be dependent upon the de novo production of TNF-alpha. We observed that prior exposure to LF resulted in a substantial inhibition of IL-1beta-induced LC migration, data again consistent with the regulation of TNF-alpha production by LF. Collectively, these results support the view that LF is able to influence cutaneous immune and inflammatory processes secondary to regulation of the production of TNF-alpha and possibly other cytokines.

Role of tumor necrosis factor in toluene diisocyanate asthma

Nearly 9 million workers are exposed to chemical agents associated with occupational asthma, with isocyanates representing the chemical class most responsible. Isocyanate-induced asthma has been difficult to diagnose and control, in part because the biologic mechanisms responsible for the disease and the determinants of exposure have not been well defined. Isocyanate-induced asthma is characterized by airway inflammation, and we hypothesized that inflammation is a prerequisite of isocyanate-induced asthma, with tumor necrosis factor (TNF)-alpha being critical to this process. To explore this hypothesis, wild-type mice, athymic mice, TNF-alpha receptor knockout (TNFR), and anti-TNF-alpha antibody-treated mice were sensitized by subcutaneous injection (20 micro l on Day 1; 5 micro l, Days 4 and 11), and challenged 7 d later by inhalation (100 ppb; Days 20, 22, and 24) with toluene diisocyanate (TDI). Airway inflammation, goblet cell metaplasia, epithelial cell damage, and nonspecific airway reactivity to methacholine challenge, measured 24 h following the last challenge, were reduced to baseline levels in TNF-alpha null mice and athymic mice. TNF-alpha deficiency also markedly abrogated TDI-induced Th2 cytokines in airway tissues, indicating a role in the development of Th2 responses. Despite abrogation of all indicators of asthma pathology, TNF-alpha neutralization had no effect on serum IgE levels or IgG-specific TDI antibodies, suggesting the lack of importance of a humoral response in the manifestation of TDI-induced asthma. Instillation studies with fluorescein-conjugated isothiocyanate and TDI suggested that TNF-alpha deficiency also resulted in a significant reduction in the migration of airway dendritic cells to the draining lymph nodes. Taken together, these results suggest that, unlike protein antigens, TNF-alpha has multiple and central roles in TDI-induced asthma, influencing both nonspecific inflammatory processes and specific immune events.

Use of mutant mice in photoimmunological and photocarcinogenic investigations

The mechanisms underlying UV-induced immunosuppression and the development of UV-induced skin cancer have been intensively investigated for decades. In particular, UV-induced DNA damage and UV-induced suppression of cellular immune responses were analyzed in great detail. During this time, several cellular and genetic pathways were identified, that are involved in photoimmunology and photocarcinogenesis. However, the direct effects of the complex UV-induced pathways on immunosuppression or on cutaneous tumor generation in vivo have not been able to be characterized with certainty so far. With the increasing availability of mutant mice that lack or overexpress certain genes, more information can be obtained with respect to the functional importance of individual gene products and the signaling pathways involved in UV-mediated immunomodulation and cancer development. This article is an overview of the results of UV-induced immunosuppression and photocarcinogenesis experiments obtained in different mutant mice.

TNF receptor subtype signalling: differences and cellular consequences

Tumour necrosis factor-alpha (TNF alpha) is a multifunctional cytokine belonging to a family of ligands with an associated family of receptor proteins. The pleiotropic actions of TNF range from proliferative responses such as cell growth and differentiation, to inflammatory effects and the mediation of immune responses, to destructive cellular outcomes such as apoptotic and necrotic cell death mechanisms. Activated TNF receptors mediate the association of distinct adaptor proteins that regulate a variety of signalling processes including kinase or phosphatase activation, lipase stimulation, and protease induction. Moreover, the cytokine regulates the activities of transcription factors, heterotrimeric or monomeric G-proteins and calcium ion homeostasis in order to orchestrate its cellular functions. This review addresses the structural basis of TNF signalling, the pathways employed with their cellular consequences, and focuses on the specific role played by each of the two TNF receptor isotypes, TNFR1 and TNFR2.

Multiple roles for tumor necrosis factor-alpha and lymphotoxin alpha/beta in immunity and autoimmunity

Tumor necrosis factor (TNF)-alpha and lymphotoxin (LT) alpha/beta play multiple roles in the development and function of the immune system. This article focuses on three important aspects of the effects of these cytokines on the immune response and on autoimmunity. In several experimental systems (Jurkat T cells, murine T-cell hybridomas), TNF-alpha appears to cause a downregulation of signaling through the TCR, revealed by changes in calcium flux, activation of p21, p23 and ZAP70, and a decrease in nuclear activation of NF-kappaB. Previous and present results suggest that TNF-alpha interferes in some manner with signaling through the TCR, at a locus yet to be delineated. Transgenic expression of LTbetaR-Fc in nonobese diabetic (NOD) transgenic mice results in prevention of type 1 diabetes in NOD mice as long as the level of expression of the fusion protein (under the control of the cytomegalovirus promoter) remains above a level of 2-3 microg/ml. Once the expression levels of the fusion protein have dropped below this critical level, the diabetic process resumes and the animals become diabetic at 40-50 weeks of age, whereas nontransgenic littermates develop diabetes by 25-30 weeks of age. The paradoxical effects of neonatal TNF-alpha administration in NOD mice in increasing incidence of and hastening onset of type 1 diabetes, while neonatal anti-TNF administration completely prevents all signs of islet cell autoimmunity, are due partly to the low levels of CD4+CD25+ T cells in NOD mice. These low levels are reduced by a further 50% on neonatal administration of nontoxic levels of TNF-alpha. In contrast, neonatal administration of anti-TNF-alpha results in a dramatic increase in the levels of CD4+CD25+ regulatory T cells, to levels beyond those seen in wild-type untreated NOD mice. TNF-alpha and LTalpha/beta thus have pleomorphic regulatory effects on the development and expression of autoimmunity.

Contribution of Langerhans cell-derived IL-18 to contact hypersensitivity

The epidermal Langerhans cells (LC), a member of the dendritic cell family, and the LC-derived cytokine IL-12 play a pivotal role in the initiation of contact hypersensitivity (CHS), a Th1 immune response in the skin. Because IL-18, another LC-derived cytokine, shares functional and biological properties with IL-12, we examined a potential role for IL-18 in CHS initiation. Our studies demonstrated that during the induction phase of murine CHS, IL-18 mRNA was significantly up-regulated in the skin-draining lymph nodes (LN). Migratory hapten-modified LC in LN expressed high levels of IL-18 mRNA and secreted functional IL-18 protein. LN cells produced significant amounts of IFN-gamma following in vitro IL-12 stimulation, which could be partially blocked by anti-IL-18 Ab, suggesting a synergistic role for endogenous IL-18 in IFN-gamma production by LN cells. Because mature IL-18 requires cleavage of immature precursors by caspase-1, we further examined IL-12-induced IFN-gamma production in caspase-1(-/-) LN cells. An impaired IFN-gamma production was seen in caspase-1(-/-) LN cells, which could be restored by addition of exogenous IL-18, supporting a role for caspase-1-cleaved, mature IL-18 in IFN-gamma production. Finally, in vivo studies showed that CHS responses were significantly inhibited in mice treated with neutralizing IL-18 Ab as well as in caspase-1(-/-) mice deficient in mature IL-18, indicating functional relevance for IL-18 in CHS. Taken together, our studies demonstrate that LC-derived IL-18 significantly contributes to CHS initiation.

Influence of ageing on Langerhans cell migration in mice: identification of a putative deficiency of epidermal interleukin-1beta

Previous studies in mice have reported a decrease in epidermal Langerhans cell (LC) density in aged skin, however, the impact of this reduction on LC function and cutaneous immune responses is unclear. In the present series of experiments, the frequency of major histocompatibility complex class II+ LC in the epidermis of older (6-month-old) mice was found to be reduced significantly compared with that observed for young (6-8-week-old) mice. LC mobilization and the subsequent accumulation of dendritic cells (DC) in regional lymph nodes in response to topical challenge with a chemical allergen were found to be less vigorous in older mice. Flow cytometric analyses of DC derived from the draining lymph nodes of fluorescein isothiocyanate (FITC)-sensitized mice revealed that the frequency of FITC+-DC arriving in draining lymph nodes was also reduced in older mice but that the fluorescence intensity was comparable. Control and allergen-treated-older mice also displayed decreased total lymph node cellularity. Contact hypersensitivity responses were found not to be compromised in older mice. However, the cytokine regulation of LC migration in the two age groups of mice did differ. LC migration provoked by intradermal injection of tumour necrosis factor-alpha (TNF-alpha) was reduced in older animals, whereas, the percentage of LC that migrated in response to exogenous interleukin-1beta (IL-1beta) was comparable for both young and aged mice. Since both allergen- and TNF-alpha-induced LC responses are known to require receipt by LC of a signal from IL-1beta for effective migration, the suggestion is that impaired LC migration in older mice may be due to a reduced availability of epidermal IL-1beta.

Increased interleukin 4 (IL-4) receptor expression and IL-4-induced decrease in IL-12 production by Langerhans cells infected with Leishmania major

Langerhans cells (LC) take up Leishmania major and are critical for the induction of the parasite-specific T-cell response. Their functional activities are regulated by cytokines. We analyzed whether infection of LC with L. major modulates the expression of their cytokine receptors. The expression of the interleukin 4 (IL-4) receptor was increased on infected LC from susceptible mice but not on those from resistant mice. Moreover, IL-4 treatment strongly decreased the lipopolysaccharide-induced IL-12 response of infected LC from susceptible mice. This modulation of IL-4 receptor expression and IL-12 production by infection of LC with Leishmania may contribute to the development of Th2 cells and to susceptibility to infection.

Tumour necrosis factor-alpha-induced migration of human Langerhans cells: the influence of ageing

BACKGROUND

Langerhans cells (LCs) play essential roles in the initiation and regulation of cutaneous immune responses mediated through their successful migration from the epidermis to draining lymph nodes while carrying antigen. Tumour necrosis factor (TNF)-alpha, a keratinocyte-derived cytokine, has recently been shown to play an important role in the mobilization of LCs from human epidermis. Although it is known that with age the immune system changes, the influence of increasing age on the function of human LCs has not been defined clearly.

OBJECTIVES

To examine the influence of age on the ability of TNF-alpha to induce LC migration.

METHODS

Ten elderly (six men, four women; mean age 76 years, range 72-79) and 10 young (six men, four women; mean age 23 years, range 18-35) volunteers received intradermal injections of 200 U of human recombinant TNF-alpha diluted in sterile saline, and control injections of sterile saline alone, at each of two paired sites identified on photoprotected buttock skin. Two hours later, paired injection sites were excised by punch biopsy. One set of paired biopsies was processed for assessment of the frequency and morphology of epidermal LCs, following preparation of epidermal sheets and immunofluorescence staining for the LC marker CD1a. The remaining paired biopsies were processed in formalin and the inflammatory response to TNF-alpha was assessed by standard histological examination.

RESULTS

Mean +/- SEM baseline values for LC frequency within epidermal sheets were significantly different between young (1156.3 +/- 38.5 cells mm(-2)) and elderly subjects (835.7 +/- 48.2 cells mm(-2); P < 0.01). Intradermal injections of 200 U of TNF-alpha caused a significant reduction in the frequency of LCs in both elderly and young subjects (P < 0.01). However, the extent of TNF-alpha-induced LC migration was substantially different between the two groups, with a mean 9% reduction in LC frequency in elderly volunteers compared with a mean 23% decrease in young subjects. Exposure to TNF-alpha was associated with a perivascular polymorphonuclear infiltrate at 2 h in all young subjects; in contrast, only 50% of the elderly individuals showed evidence of such a response.

CONCLUSIONS

There are significant differences between young and old skin with respect to both resting LC numbers and their response to TNF-alpha. These age-related changes in LC frequency and function may contribute to the altered cutaneous immune function observed in the elderly.

Dendritic cell migration to lymph nodes: cytokines, chemokines, and lipid mediators

Mobilization of dendritic cells into lymphatic vessels requires cytokine stimulation and induction of the chemokine receptor CCR7. The respective roles of the CCR7 ligands CCL19 and CCL21 in mediating migration are not fully defined, but chemotaxis to CCL19 mediates Langerhans cell exit from the epidermis. Optimal chemotaxis to CCL19 occurs when DCs are triggered with exogenous leukotriene C(4), an eicosanoid transported out of the cell via the ATP binding cassette (ABC) transporter multidrug resistance related protein 1 (MRP1, ABCC1). Indeed, MRP1 and the related multidrug resistance protein 1 (MDR1, p-glycoprotein, ABCB1) may control the intracellular and extracellular accumulation of key signaling lipids that regulate dendritic cell migration.

Interleukin-1beta but not tumor necrosis factor is involved in West Nile virus-induced Langerhans cell migration from the skin in C57BL/6 mice

Langerhans cells are bone marrow-derived epidermal dendritic cells. They migrate out of the epidermis into the lymphatics and travel to the draining lymph nodes where they are responsible for the activation of T cells in the primary immune response. Tumor necrosis factor and interleukin-1beta, have previously been shown to be responsible for Langerhans cell migration in response to contact sensitizers in BALB/C mice; however, which cytokines are responsible for mediating Langerhans cell migration in response to a replicating cutaneously acquired virus such as the West Nile Virus, are not known. We have devised a method for identifying Langerhans cells in the draining lymph nodes using E-cadherin labeling and flow cytometry. We infected tumor necrosis factor-deficient gene knockout mice (tumor necrosis factor-/-) intradermally with West Nile Virus and found that levels of Langerhans cell emigration and accumulation in the draining lymph nodes were similar to wild-type C57BL/6 mice. This was borne out by the finding that high levels of systemic neutralizing anti-tumor necrosis factor antibody failed to inhibit the migration of Langerhans cells from the epidermis and their accumulation in the draining lymph nodes in wild-type C57BL/6 mice. In West Nile Virus-infected, tumor necrosis factor-/- mice treated with systemic neutralizing anti-interleukin-1beta antibodies, however, migration of Langerhans cells from the epidermis and their accumulation in the draining lymph nodes were significantly inhibited compared with control antibody-treated, infected animals. The results indicate that Langerhans cell migration, accumulation in the draining lymph nodes and the initiation of lymph node shut-down in response to a cutaneous West Nile Virus infection is dependent on interleukin-1beta and can occur in the absence of tumor necrosis factor.

Inflammatory skin disease in K14/p40 transgenic mice: evidence for interleukin-12-like activities of p40

The proinflammatory cytokine interleukin-12, a p35/p40 heterodimer, is produced by resident cells in skin and has been implicated as a pathogenetic factor in T-cell-mediated skin diseases. Secretion of heterodimeric interleukin-12 is always accompanied by production of p40 monomer and p40/p40 homodimer. To investigate the possible in vivo role of p40 per se, we generated mice that constitutively express monomeric and homodimeric p40 in basal keratinocytes. These mice spontaneously developed an eczematous skin disease that was characterized by hyperkeratosis, focal epidermal spongiosis, and a mixed inflammatory infiltrate composed of T cells (CD4+), macrophages, eosinophils, mast cells, and few neutrophils. Fluorescence-activated cell sorter analysis of transgenic epidermal cell suspensions revealed induction of major histocompatibility complex class II molecules on keratinocytes and a 2-3-fold increase in the content of Langerhans cells. Cytokines produced by these activated epidermal cells include interleukin-1alpha and tumor necrosis factor alpha. The skin disease in K14/p40 mice was similar to that of littermate mice that received injections of interleukin-12, suggesting overlapping in vivo functional properties. As induction of interferon-gamma is a major function of interleukin-12, we tested the in vitro ability of transgenic p40 to induce interferon-gamma. In contrast to interleukin-12, transgenic p40 did not stimulate interferon-gamma secretion by cultured splenocytes. We conclude that transgenic p40 and interleukin-12 are equally capable of initiating cutaneous inflammation. Despite these in vivo similarities, there is a clear functional difference between interleukin-12 and transgenic p40 in vitro, suggesting that interferon-gamma is not a major factor contributing to interleukin-12-like activities of transgenic p40.

Rethinking the role of tumour necrosis factor-alpha in ultraviolet (UV) B-induced immunosuppression: altered immune response in UV-irradiated TNFR1R2 gene-targeted mutant mice

BACKGROUND

Ultraviolet (UV) B-induced immunosuppression, implicated in the pathogenesis of skin cancers, is postulated to be mediated in part by cis-urocanic acid (cis-UCA) via tumour necrosis factor (TNF)-alpha. TNF-alpha produces morphological changes in Langerhans cells indistinguishable from those induced by UVB exposure and antibodies against TNF-alpha have been demonstrated to inhibit UVB-induced immunosuppression in vivo.

OBJECTIVES

To clarify further the role of TNF-alpha in UVB-induced immunosuppression and in cis-UCA immunosuppression.

METHODS

We performed a contact hypersensitivity (CHS) assay on gene-targeted mutant mice (TNFR1R2-/-) lacking genes for both receptors (p55 and p75) for TNF-alpha. Mice were either irradiated with UVB or injected intradermally with cis-UCA, sensitized with 2,4-dinitrofluorobenzene, challenged on the ears and the response was measured.

RESULTS

The TNFR1R2-/- mice showed hyporesponsiveness in the CHS response compared with wild-type (P < 0.001), confirming the proinflammatory role of TNF-alpha. However, significant suppression of CHS was seen after irradiation and after cis-UCA injection in both locally (sensitization on irradiated site; P < 0.05) and systemically (sensitization on non-irradiated site; P < 0.05) sensitized wild-type and gene-targeted mice.

CONCLUSIONS

These results demonstrate that TNF-alpha signalling is only partially involved in UVB-induced immunosuppression and does not play a major part in the cis-UCA immunosuppression mechanism.

Exogenous topical lactoferrin inhibits allergen-induced Langerhans cell migration and cutaneous inflammation in humans

BACKGROUND

Lactoferrin (LF), an iron-binding protein found in exocrine secretions, is known to possess antibacterial properties. It has recently been proposed that LF may also influence inflammatory reactions.

OBJECTIVES

To characterize in humans the ability of recombinant homologous LF to inhibit the induced migration of epidermal Langerhans cells (LCs) from the skin, a process known to be dependent upon the proinflammatory cytokines tumour necrosis factor (TNF)-alpha and interleukin 1beta and to influence cutaneous inflammatory reactions.

METHODS

We investigated the anti-inflammatory properties of LF in human volunteers.

RESULTS

Topical exposure to LF 2 h prior to sensitization caused a significant reduction in contact allergen (diphenylcyclopropenone, DPC)-induced LC migration from the epidermis as judged by the altered frequency of cells expressing either HLA-DR or CD1a determinants. That this reduction was secondary to an inhibition of TNF-alpha production was indicated by the fact that LF failed to influence LC migration induced by intradermal injection of this cytokine. In approximately 50% of those volunteers who displayed local inflammation in response to DPC, LF was found to cause a discernible reduction in the clinical severity of the reaction, associated with reduced infiltration of inflammatory cells.

CONCLUSIONS

These data demonstrate that LF is able to influence cutaneous immune and inflammatory responses, possibly because of an impaired production of local proinflammatory cytokines.

Interleukin (IL)-18 induces Langerhans cell migration by a tumour necrosis factor-alpha- and IL-1beta-dependent mechanism

Following skin sensitization a proportion of epidermal Langerhans cells (LC) are stimulated to leave the skin and to migrate, via afferent lymphatics, to draining lymph nodes where they accumulate as immunostimulatory dendritic cells (DC). It has been demonstrated previously that tumour necrosis factor-alpha (TNF-alpha), an inducible product of epidermal keratinocytes, and interleukin (IL)-1beta, produced exclusively by LC in murine epidermis, provide important signals for the initiation of this response. Recently, it has been demonstrated that IL-18, a cytokine produced by both LC and keratinocytes within the epidermis, may also participate in immune responses induced following skin sensitization. In the present investigations, the ability of IL-18 to contribute to the regulation of LC migration and the accumulation of DC in draining lymph nodes has been examined. It was found that, like IL-1beta, IL-18 administered intradermally to mice resulted in a significant reduction in epidermal major histocompatibility complex (MHC) class II+ LC densities and a marked increase in lymph node DC numbers. Using neutralizing anti-TNF-alpha and blocking anti-type I IL-1 receptor (IL-1RI) antibodies, it was shown also that the induction by IL-18 of both LC mobilization and DC accumulation in regional lymph nodes was dependent upon availability of TNF-alpha and the integrity of IL-1RI signalling. Furthermore, using IL-1beta converting enzyme (caspase-1) knockout mice, IL-18-induced LC migration was found to have a mandatory requirement for active IL-1beta. Importantly, not only was IL-18 able to contribute to the regulation of LC migration, it was found to be essential for the manifestation of these processes in response to topical sensitization with the contact allergen oxazolone.

Migration of dendritic cells into lymphatics-the Langerhans cell example: routes, regulation, and relevance

Dendritic cells are leukocytes of bone marrow origin. They are central to the control of the immune response. Dendritic cells are highly specialized in processing and presenting antigens (microbes, proteins) to helper T lymphocytes. Thereby, they critically regulate further downstream processes such as the development of cytotoxic T lymphocytes, the production of antibodies by B lymphocytes, or the activation of macrophages. A new field of dendritic cell biology is the study of their potential role in inducing peripheral tolerance. The immunogenic/tolerogenic potential of dendritic cells is increasingly being utilized in immunotherapy, particularly for the elicitation of antitumor responses. One very important specialization of dendritic cells is their outstanding capacity to migrate from sites of antigen uptake to lymphoid organs. Much has been learned about this process from studying one particular type of dendritic cell, namely, the Langerhans cell of the epidermis. Therefore, the migratory properties of Langerhans cells are reviewed. Knowledge about this "prototype dendritic cell" may help researchers to understand migration of other types of dendritic cells.

CD4+ Th1 and CD8+ type 1 cytotoxic T cells both play a crucial role in the full development of contact hypersensitivity

The role of CD4(+) vs CD8(+) T cells in contact hypersensitivity (CHS) remains controversial. In this study, we used gene knockout (KO) mice deficient in CD4(+) or CD8(+) T cells to directly address this issue. Mice lacking either CD4(+) or CD8(+) T cells demonstrated depressed CHS responses to dinitrofluorobenzene and oxazolone compared with wild-type C57BL/6 mice. The depression of CHS was more significant in CD8 KO mice than in CD4 KO mice. Furthermore, in vivo depletion of either CD8(+) T cells from CD4 KO mice or CD4(+) T cells from CD8 KO mice virtually abolished CHS responses. Lymph node cells (LNCs) from hapten-sensitized CD4 and CD8 KO mice showed a decreased capacity for transferring CHS. In vitro depletion of either CD4(+) T cells from CD8 KO LNCs or CD8(+) T cells from CD4 KO LNCs resulted in a complete loss of CHS transfer. LNCs from CD4 and CD8 KO mice produced significant amounts of IFN-gamma, indicating that both CD4(+) and CD8(+) T cells are able to secrete IFN-gamma. LNCs from CD8, but not CD4, KO mice were able to produce IL-4 and IL-10, suggesting that IL-4 and IL-10 are mainly derived from CD4(+) T cells. Intracellular cytokine staining of LNCs confirmed that IFN-gamma-positive cells consisted of CD4(+) (Th1) and CD8(+) (type 1 cytotoxic T) T cells, whereas IL-10-positive cells were exclusively CD4(+) (Th2) T cells. Collectively, these results suggest that both CD4(+) Th1 and CD8(+) type 1 cytotoxic T cells are crucial effector cells in CHS responses to dinitrofluorobenzene and oxazolone in C57BL/6 mice.

Changes in the motility, morphology, and F-actin architecture of human dendritic cells in an in vitro model of dendritic cell development

An in vitro model has been developed for analyzing the two developmental phases of human dendritic cell (DC) migration. Employing the age of the culture and the addition of GM-CSF, IL-4, and serum to regulate cellular phenotype, and glass coated with acid-precipitated human plasma proteins to facilitate persistent DC translocation, the model produces three sequential in vitro phenotypes with the following suggested in vivo counterparts: (1) DCs recently isolated from blood, which are highly polar and motile, and reflect the behavior of "undifferentiated" DCs that must extravasate from the blood stream and migrate into peripheral tissue; (2) large, nonmotile, stellate DCs, which reflect the highly "differentiated" signature phenotype of DCs in peripheral tissue, whose function is to capture foreign antigens; and (3) the large, motile "dedifferentiated" DCs, which reflect the behavior of "veiled cells" that have captured an antigen, retracted dendritic processes, migrated out of peripheral tissue, and are in the process of transporting a captured antigen to a proximal draining lymph node for presentation to T cells. Computer-assisted motion analysis of the three sequential phenotypes and fluorescent staining of F-actin reveal three unique behavioral states and unique cellular architecture consistent with inferred in vivo function. This in vitro model should serve as a starting point for elucidating the cues and molecular mechanisms involved in the regulation of DC differentiation and motility.

Cytokines and chemokines in the initiation and regulation of epidermal Langerhans cell mobilization

Langerhans cells (LC) are members of the wider family of dendritic cells. LC reside in the epidermis where they serve as sentinels of the immune system, their responsibilities being to sample the external environment for changes and challenges and to deliver information (antigen) to responsive T lymphocytes within skin draining lymph nodes. The ability of LC to migrate from the epidermis to regional lymph nodes is therefore of pivotal importance to the induction of cutaneous immune responses. The journey that LC have to make from the skin has a number of requirements. Initially it is necessary that LC disassociate themselves from surrounding keratinocytes and are liberated from other influences that encourage their retention in the epidermis. Subsequently, migrating LC must successfully traverse the basement membrane of the dermal-epidermal junction and make their way, via afferent lymphatics, to draining lymph nodes. Effective entry into lymph nodes is necessary, as is correct positioning of cells within the paracortex. There is increasing evidence that both cytokines and chemokines, and their interaction with appropriate receptors expressed by LC, orchestrate the mobilization and movement of these cells. We here consider the parts played by these molecules, and how collectively they induce and direct LC migration.

Imiquimod, a topical immune response modifier, induces migration of Langerhans cells

Langerhans cells are bone marrow derived dendritic cells that represent the major antigen-presenting cells in the skin. Langerhans cells take up and process antigen within the epidermis and present processed antigen to T lymphocyte in the regional lymph nodes and thus form an integral part of the cutaneous immune response. The cutaneous immune response can be modified by a number of pharmacologic agents, including corticosteroids, cyclosporine, and retinoids as well as physical agents, such as ultraviolet light. For the most part these agents act by suppressing immune function. A topical immune response modifier, imiquimod has been shown to enhance the cutaneous immune response. Imiquimod has anti-viral and anti-tumor effects in animal models and has been approved for the topical treatment of external genital and perianal warts in humans. The biologic activity of imiquimod in part is due to its effect as a cytokine inducer. Preliminary data suggested that imiquimod could have an effect on Langerhans cells. In order to clarify this effect on Langerhans cells, we examined Langerhans cell morphology and migration in imiquimod-treated skin. The density of Ia + cells decreased 2 d after treatment, falling to approximately 43% by day 10. The Ia positive in cells remaining in the skin appeared larger and more dendritic suggesting an activated state. ATPase staining of epidermal sheet confirmed the decreased number of Langerhans cells. To clarify status of Langerhans cells, the activation of B7 was examined. Activation of B7-1 or B7-2 was not detected. Imiquimod, however, did enhance Langerhans cell migration from skin to draining lymph nodes. This enhanced Langerhans cell migration was also associated with an enhanced allergic contact hypersensitivity. These results suggest that the mechanism of modulation of immune response by imiquimod is in part due to effects on Langerhans cells.

Differential effects of cytokines and immunosuppressive drugs on CD40, B7-1, and B7-2 expression on purified epidermal Langerhans cells1

Langerhans cells are MHC class II antigen-positive antigen-presenting cells in the epidermis. Recent studies have revealed that Langerhans cells express costimulatory molecules like B7-1 and B7-2 and the accessory molecule CD40. Although these molecules are important for the antigen-presenting function of Langerhans cells, little is known about the precise regulation of their expression on purified Langerhans cells. Using a panning technique, we purified epidermal Langerhans cells to around 95% purity. Freshly prepared Langerhans cells (fLC) expressed the mRNA for receptors for M-CSF (cfms), GM-CSF (GM-CSFR), and TNF-alpha (TNFRII). TNF-alpha markedly upregulated CD40 and B7-1 expression on Langerhans cells, but not B7-2 expression. GM-CSF moderately upregulated B7-1 and B7-2 expression, and slightly upregulated CD40 expression. M-CSF moderately upregulated B7-1 expression, but did not modulate CD40 or B7-2 expression. Dexamethasone (DEX) markedly inhibited CD40, B7-1, and B7-2 expression on Langerhans cells. Cyclosporin A (CsA) and FK506 slightly inhibited CD40 and B7-1 expression on Langerhans cells, but not B7-2. Furthermore, TNF-alpha restored the DEX-induced inhibition of CD40 expression on Langerhans cells, but not the inhibition of B7-1 or B7-2 expression. GM-CSF restored DEX-induced inhibition of CD40, B7-1, and B7-2 expression. M-CSF did not affect the DEX-induced inhibition of these molecule expressions. These data provide a better understanding of the role of selective cytokines and immunosupressive drugs in the modulation of the antigen-presenting capacity of Langerhans cells.

Increased gammadelta T-cell populations in draining lymph nodes of lambs during the elicitation phase of dinitrochlorobenzene-induced contact hypersensitivity

Ten lambs were sensitised with the hapten DNCB in an acetone/olive oil vehicle. The hapten/vehicle solution was applied onto the skin on the shaved ventral surface of the right ear. Two weeks later these lambs were rechallenged with the DNCB/vehicle solution. Simultaneously, ten non-sensitised lambs were treated with vehicle only, serving as vehicle controls. The 20 lambs were slaughtered 48 h after challenge/vehicle treatment, along with ten untreated animals serving as normal controls. Specimens of draining lymph nodes were collected from the 30 animals. All lambs were between 149 and 187 days old. Lymph node cryosections were stained for several leukocyte markers using monoclonal antibodies with the ABC immunohistochemical method. The stained sections were subsequently assessed in three different cortical compartments in each section, using an image analysis system. The resulting measurements from the three groups were compared. A marked increase of gammadelta T cells was detected in the DNCB group. The number of CD4+ T helper cells was decreased in the DNCB group compared with the normal control group, but not with the vehicle control group. No differences were revealed for CD8+ T cytotoxic cells or B cells. These findings were interpreted to be the consequences of possible downregulatory mechanisms protecting the lymphoid tissue from hypersensitivity. The prominence of gammadelta T-cells could indicate that these cells are involved in downregulation.