Immune Cell-Stromal Circuitry in Lupus Photosensitivity

Photosensitivity is a sensitivity to UV radiation (UVR) commonly found in systemic lupus erythematosus (SLE) patients who have cutaneous disease. Upon even ambient UVR exposure, patients can develop inflammatory skin lesions that can reduce the quality of life. Additionally, UVR-exposed skin lesions can be associated with systemic disease flares marked by rising autoantibody titers and worsening kidney disease. Why SLE patients are photosensitive and how skin sensitivity leads to systemic disease flares are not well understood, and treatment options are limited. In recent years, the importance of immune cell-stromal interactions in tissue function and maintenance is being increasingly recognized. In this review, we discuss SLE as an anatomic circuit and review recent findings in the pathogenesis of photosensitivity with a focus on immune cell-stromal circuitry in tissue health and disease.

Lymphatic Function in Autoimmune Diseases

Lymphatic vessels are critical for clearing fluid and inflammatory cells from inflamed tissues and also have roles in immune tolerance. Given the functional association of the lymphatics with the immune system, lymphatic dysfunction may contribute to the pathophysiology of rheumatic autoimmune diseases. Here we review the current understanding of the role of lymphatics in the autoimmune diseases rheumatoid arthritis, scleroderma, lupus, and dermatomyositis and consider the possibility that manual therapies such as massage and acupuncture may be useful in improving lymphatic function in autoimmune diseases.

Ultraviolet Radiations: Skin Defense-Damage Mechanism

UV-radiations are the invisible part of light spectra having a wavelength between visible rays and X-rays. Based on wavelength, UV rays are subdivided into UV-A (320-400 nm), UV-B (280-320 nm) and UV-C (200-280 nm). Ultraviolet rays can have both harmful and beneficial effects. UV-C has the property of ionization thus acting as a strong mutagen, which can cause immune-mediated disease and cancer in adverse cases. Numbers of genetic factors have been identified in human involved in inducing skin cancer from UV-radiations. Certain heredity diseases have been found susceptible to UV-induced skin cancer. UV radiations activate the cutaneous immune system, which led to an inflammatory response by different mechanisms. The first line of defense mechanism against UV radiation is melanin (an epidermal pigment), and UV absorbing pigment of skin, which dissipate UV radiation as heat. Cell surface death receptor (e.g. Fas) of keratinocytes responds to UV-induced injury and elicits apoptosis to avoid malignant transformation. In addition to the formation of photo-dimers in the genome, UV also can induce mutation by generating ROS and nucleotides are highly susceptible to these free radical injuries. Melanocortin 1 receptor (MC1R) has been known to be implicated in different UV-induced damages such as pigmentation, adaptive tanning, and skin cancer. UV-B induces the formation of pre-vitamin D3 in the epidermal layer of skin. UV-induced tans act as a photoprotection by providing a sun protection factor (SPF) of 3-4 and epidermal hyperplasia. There is a need to prevent the harmful effects and harness the useful effects of UV radiations.

Photoprotective and immunoregulatory capacity of ginsenoside Rg1 in chronic ultraviolet B-irradiated BALB/c mouse skin

The aim of this study was to investigate the photoprotective and immunoregulatory capacities of ginsenoside Rg1 in skin irradiated by chronic ultraviolet B (UVB) and to verify the potential mechanisms of action. BALB/c mice were pretreated with a topical application of ginsenoside Rg1 and irradiated with different doses of UVB daily for 30 consecutive days. Following chronic UVB irradiation, there were significant pathological changes in the skin of the BALB/c mice, including hyperkeratosis, acanthosis, sponge-like edematization and sunburn occurring in the epidermis, while edema, telangiectasis and inflammatory cell infiltration were observed in the papillary layer of the dermis. Treatment with ginsenoside Rg1 was able to reduce such changes induced by UVB irradiation. The number of p53 protein-positive stained cells following UVB irradiation was also observed by immunohistochemical analysis. Ginsenoside Rg1 downregulated the p53 protein expression induced by UVB irradiation, leading to reductions of 69.50, 23.53 and 12.93% at doses of 30, 60 and 120 mJ/cm², respectively. Using reverse transcription polymerase chain reaction (RT-PCR), reductions in the levels of interferon (IFN)-γ mRNA expression were detected following UVB exposure; reductions of 19.6, 36.3 and 39.6% were observed following UVB irradiation at doses of 30, 60 and 120 mJ/cm², respectively. The interleukin (IL)-10 mRNA expression levels increased by 40.1, 71.0 and 89.4% and the tumor necrosis factor (TNF)-α mRNA expression levels increased by 36.4, 18.4 and 8.6% following UVB irradiation at doses of 30, 60 and 120 mJ/cm², respectively. However, pretreatment with ginsenoside Rg1 was observed to markedly attenuate the UVB irradiation-induced effects on the mRNA expression levels of the three cytokines. The topical application of ginsenoside Rg1 was able to protect the irradiated skin from UVB injury and reduce UVB-induced p53 protein expression. Ginsenoside Rg1 also demonstrated a potential regulatory effect on the UVB-induced local expression of the mRNA of the cytokines IFN-γ, IL-10 and TNF-α, which may be important in its immunoregulatory and inflammatory mechanisms.

Adoptive transfusion of tolerance dendritic cells prolongs the survival of skin allografts in mice: a systematic review

OBJECTIVE

We aim to systematically review adoptive transfusion of tolerogenic dendritic cells (Tol-DCs) induced by different ways to affect skin allograft survival in mice.

METHODS

We searched PubMed and EMbase for relevant studies and evaluated the quality of included ones. Taking skin allograft survival time as endpoint outcome, we displayed outcomes of each group using one forest map and dissected possible mechanisms underlying survival prolongation.

RESULTS

We included 21 studies, which reported four methods of inducing Tol-DCs with different extents of average allograft survival prolongation: skin allograft survival time was prolonged (the drug intervention group, 63.08 ± 42.92 days, 4.6 folds to control; the cytokine induction group: 26.17 ± 16.20 days, 1.8 folds; the gene modification group: 14.65 ± 17.89 days, 1.5 folds; other derivation group 9.63 ± 24.38 days, 0.5 fold). Possible mechanisms underlying survival prolongation included induction of donor-specific T cell hyporesponsiveness, reduction of cytotoxicity against allografts, Th0 skewing to Th2, and generation or expansion of Treg. Infusion of Tol-DCs in combination with immunosuppressive agents or costimulatory blockade contributed to longer prolongation. Compared to MiHA mismatch, MHCI/II mismatch was a much more important factor to cause skin allograft rejection.

CONCLUSION

For MHC or MiHA mismatched, allogeneic skin transplants inbred recipients, adoptive transfusion of Tol-DCs induced by 4 methods prolong skin allograft survival to different extents. Drug intervened Tol-DCs works best. Immunosuppressive agents and/or co-stimulatory blockade contribute to better outcomes. Yet more rigorous studies with larger sample size are needed and more attention to mechanisms should be paid.

Development of the prenatal cutaneous antigen-presenting cell network

The skin, and in particular the epidermis, is a physical barrier that protects the body from external threats and is critically involved in immune reactivity. Professional antigen-presenting cells, such as epidermal Langerhans cells and dermal dendritic cells, are gaining prominence as principal players orchestrating the decision between immunity and tolerance. A focus of research interest in recent years has been the investigation of these cells in mammalian prenatal skin. In this review, we will compare the recent progress in dissecting the phenotype and functional role of antigen-presenting cells in the developing human and mouse skin before birth and perinatally, and will discuss how this knowledge improves our understanding of the level of immunocompetence of the skin in utero.

Galectin-2 suppresses contact allergy by inducing apoptosis in activated CD8+ T cells

Galectins, a family of structurally related beta-galactoside-binding proteins, are expressed by various cells of the immune systems and seem to be important for the regulation of immune responses and immune cell homeostasis. Since it has been demonstrated that galectin-2 regulates cell-mediated inflammatory bowel disease and colitis in mice, we intended to investigate the role of galectin-2 in inflammatory cutaneous T cell-mediated immune responses. To address this issue, groups of naive mice were sensitized to the contact allergen 2,4-dinitro-1-fluorobenzene and systemically treated with galectin-2 to analyze the effects of galectin-2 on contact allergy. Here we show that galectin-2 is expressed in murine skin and is up-regulated upon cutaneous inflammation. Interestingly, treatment of mice with galectin-2 significantly reduced the contact allergy response. This effect was long-lasting since rechallenge of galectin-2-treated mice after a 14-day interval still resulted in a decreased ear swelling. We were able to demonstrate that galectin-2 induced a reduction of MHC class I-restricted immune responses in the treated animals, which was mediated by the induction of apoptosis specifically in activated CD8(+) T cells. Additionally, we report that the galectin-2-binding protein CD29 is up-regulated on the surface of activated CD8(+) T cells compared with naive CD8(+) T cells or CD4(+) T cells, suggesting that increased galectin-2/CD29 signaling might be responsible for the proapoptotic effects of galectin-2 on activated CD8(+) T cells. Taken together, these data indicate that galectin-2 may represent a novel therapeutic alternative for the treatment of CD8-mediated inflammatory disorders such as contact allergy.

Adjuvant effect of lipopolysaccharide on the induction of contact hypersensitivity to haptens in mice

BACKGROUND

Toll-like receptor (TLR) 4 is a critical receptor and signal transducer for lipopolysaccharide (LPS), a major component of Gram-negative bacteria. The MyD88-independent pathway downstream of TLR4 leads to functional dendritic cell (DC) maturation, although LPS-induced cytokine production from DCs is MyD88-dependent.

OBJECTIVES

We investigated whether intracutaneously injected LPS alters the functions of cutaneous DCs, leading to enhanced contact hypersensitivity (CH).

METHODS

The ear swelling response was measured to evaluate the magnitude of CH. Cell proliferation of allogeneic splenocytes stimulated by DC-enriched draining lymph node (LN) cells was measured by performing a [(3)H]-thymidine incorporation assay. Epidermal I-A+ cells were evaluated under an epifluorescent microscope. I-A+ FITC-bearing cells from the draining LNs 24h after FITC application were analyzed on FACScan.

RESULTS

LPS augmented CH induction in C3H/HeN (HeN) and MyD88-knockout (KO) mice but not in C3H/HeJ (HeJ) and H-2S(d)-bearing strains such as BALB/c mice. LPS failed to augment the allo-stimulatory ability of DCs in the draining LNs after hapten applications. LPS altered the density and morphology of epidermal I-A+ cell in HeN and BALB/c mice but not in TLR4-deficient HeJ mice. LPS increased the proportion of I-A+ FITC-bearing cells in the LNs 24h after FITC application in HeN, but not in BALB/c and HeJ.

CONCLUSIONS

LPS augments the ability of DCs to migrate to the draining LNs, leading to enhanced CH via a TLR4-dependent, MyD88-independent pathway. The different effects of LPS on CH in some strains of mice may explain individual differences in the susceptibility to establish CH to daily antigen exposures in clinical settings.

Molecular and cellular mechanisms of photocarcinogenesis

Skin cancer constitutes one of the most frequent types of malignancies in humans with rapidly increasing incidences almost worldwide. UVR is an essential risk factor for the development of premalignant as well as malignant skin lesions. In this context UVR can function as a complete carcinogen by inducing "UV signature" DNA mutations and by suppressing protective cellular antitumoral immune responses. UV-induced DNA damage can result in impaired cutaneous cell cycle control if cell cycle regulators, such as the p53 gene, are affected. Besides interfering with cell cycle control genes, UV-induced DNA damage can result in the release of interleukin-10, a cytokine with known immunosuppressive effects on T-helper(h)-1 cells. For the development of antitumoral immune responses antigen-specific activation of effector T cells by antigen-presenting cells (APC) is required. It was demonstrated that UVR can inhibit antigen presentation both directly and indirectly via the induction of suppressive cytokines. In addition, subsets of T cells are induced upon UVR, which can actively suppress major histocompatibility complex class I/II-restricted immune responses. These UV-induced regulatory T cells appear to belong to the CD4+CD25+ T cell lineage and can express the characteristic transcription factor Foxp3, which programs for suppressor function. In mice UV-induced regulatory T cells can control the development of UV-induced skin cancer. Peripheral regulatory T cells are maintained by the expression of B7 molecules and can be expanded by APC of the skin. Recently, epidermal expression of CD254 (RANKL) has been shown to connect UVR with the expansion of regulatory CD4+CD25+ T cells. In the following, new molecular and cellular mechanisms of UV-induced skin tumor development will be described and discussed.

IL-10 is excluded from the functional cytokine memory of human CD4+ memory T lymphocytes

Epigenetic modifications, including DNA methylation, profoundly influence gene expression of CD4(+) Th-specific cells thereby shaping memory Th cell function. We demonstrate here a correlation between a lacking fixed potential of human memory Th cells to re-express the immunoregulatory cytokine gene IL10 and its DNA methylation status. Memory Th cells secreting IL-10 or IFN-gamma were directly isolated ex vivo from peripheral blood of healthy volunteers, and the DNA methylation status of IL10 and IFNG was assessed. Limited difference in methylation was found for the IL10 gene locus in IL-10-secreting Th cells, as compared with Th cells not secreting IL-10 isolated directly ex vivo or from in vitro-established human Th1 and Th2 clones. In contrast, in IFN-gamma(+) memory Th cells the promoter of the IFNG gene was hypomethylated, as compared with IFN-gamma-nonsecreting memory Th cells. In accordance with the lack of epigenetic memory, almost 90% of ex vivo-isolated IL-10-secreting Th cells lacked a functional memory for IL-10 re-expression after restimulation. Our data indicate that IL10 does not become epigenetically marked in human memory Th cells unlike effector cytokine genes such as IFNG. The exclusion of IL-10, but not effector cytokines, from the functional memory of human CD4(+) T lymphocytes ex vivo may reflect the need for appropriate regulation of IL-10 secretion, due to its potent immunoregulatory potential.

IL-10 controls ultraviolet-induced carcinogenesis in mice

UV radiation-induced immunosuppression contributes significantly to the development of UV-induced skin cancer by inhibiting protective immune responses. IL-10 has been shown to be a key mediator of UV-induced immunosuppression. To investigate the role of IL-10 during photocarcinogenesis, groups of IL-10(+/+), IL-10(+/-), and IL-10(-/-) mice were chronically irradiated with UV. IL-10(+/+) and IL-10(+/-) mice developed skin cancer to similar extents, whereas IL-10(-/-) mice were protected against the induction of skin malignancies by UV. Because UV is able to induce regulatory T cells, which play a role in the suppression of protective immunity, UV-induced regulatory T cell function was analyzed. Splenic regulatory T cells from UV-irradiated IL-10(-/-) mice were unable to confer immunosuppression upon transfer into naive recipients. UV-induced CD4+CD25+ T cells from IL-10(-/-) mice showed impaired suppressor function when cocultured with conventional CD4+CD25- T cells. CD4+CD25- T cells from IL-10(-/-) mice produced increased amounts of IFN-gamma and enhanced numbers of CD4+TIM-3+ T cells were detectable within UV-induced tumors in IL-10(-/-) mice, suggesting strong Th1-driven immunity. Mice treated with CD8+ T cells from UV-irradiated IL-10(-/-) mice rejected a UV tumor challenge significantly faster, and augmented numbers of granzyme A+ cells were detected within injected UV tumors in IL-10(-/-) animals, suggesting marked antitumoral CTL responses. Together, these findings indicate that IL-10 is critically involved in antitumoral immunity during photocarcinogenesis. Moreover, these results point out the crucial role of Th1 responses and UV-induced regulatory T cell function in the protection against UV-induced tumor development.

Ultraviolet B irradiation selectively increases the production of interleukin-8 in human cord blood-derived mast cells

UVB irradiation modulates immune responses in the skin and is a major cause of sunburn, during which neutrophils accumulate in the skin. Because of their abundance in skin and ability to produce a variety of proinflammatory mediators, we propose that mast cells may play a key role in ultraviolet B (UVB)-induced skin inflammation. Cord blood-derived human mast cells were treated in vitro with varying doses of UVB and production of multiple cytokines was measured in culture supernatants. UVB exposure significantly increased the release of interleukin (IL)-8 and modestly increased IL-1alpha production, but cytokines such as IL-2, IL-4, IL-6, IL-10, IL-12, IL-13, tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma were unaffected. Cycloheximide reduced the UVB-mediated induction of IL-8 by 30-40%, suggesting that new protein synthesis contributed to IL-8 production. In line with this, UVB treatment of mast cells significantly increased IL-8 mRNA. In contrast to its effect on IL-8 production, optimal doses of UVB did not provoke histamine or tryptase release, indicating little effect on degranulation. Our data suggest that mast cells may play a major role during UVB-induced acute inflammation by selectively inducing cytokines involved in neutrophil recruitment.

Cathelicidin Antimicrobial Peptides Block Dendritic Cell TLR4 Activation and Allergic Contact Sensitization

Cathelicidins are antimicrobial peptides of the innate immune system that establish an antimicrobial barrier at epithelial interfaces and have been proposed to have a proinflammatory function. We studied the role of cathelicidin in allergic contact dermatitis, a model requiring dendritic cells of the innate immune response and T cells of the adaptive immune response. Deletion of the murine cathelicidin gene Cnlp enhanced an allergic contact response, whereas local administration of cathelicidin before sensitization inhibited the allergic response. Cathelicidins inhibited TLR4 but not TLR2 mediated induction of dendritic cell maturation and cytokine release, and this inhibition was associated with an alteration of cell membrane function and structure. Further analysis in vivo connected these observations because inhibition of sensitization by exogenous cathelicidin was dependent on the presence of functional TLR4. These observations provide evidence that cathelicidin antimicrobial peptides mediate an anti-inflammatory response in part by their activity at the membrane.

Photosensitivity in lupus erythematosus

Lupus erythematosus (LE) is an autoimmune disease which can be triggered by environmental factors such as solar irradiation. It has long been observed that especially ultraviolet (UV) exposure can induce and exacerbate skin lesions in patients with this disease. However, despite the frequency of photosensitivity in LE, the mechanisms by which UV irradiation activates autoimmune responses is only now becoming increasingly unfolded by advanced molecular and cellular biological investigations. Phototesting, according to a standardized protocol with UVA and UVB irradiation has proven to be a valid model to study photosensitivity in various subtypes of LE and to evaluate the underlying pathomechanisms of this disease. Detailed analysis of the molecular events that govern lesion formation in experimentally photoprovoced LE showed increased accumulation of apoptotic keratinocytes and impaired expression of the inducible nitric oxide synthase (iNOS). In the near future, gene expression profiling and proteomics will further increase our knowledge on the complexity of the "UV response" in LE. This review summarizes the current understanding of the clinical and molecular mechanisms that initiate photosensitivity in this disease.

Augmentation of cutaneous immune responses by ATP gamma S: purinergic agonists define a novel class of immunologic adjuvants

Extracellular nucleotides activate ligand-gated P2XR ion channels and G protein-coupled P2YRs. In this study we report that intradermal administration of ATPgammaS, a hydrolysis-resistant P2 agonist, results in an enhanced contact hypersensitivity response in mice. Furthermore, ATPgammaS enhanced the induction of delayed-type hypersensitivity to a model tumor vaccine in mice and enhanced the Ag-presenting function of Langerhans cells (LCs) in vitro. Exposure of a LC-like cell line to ATPgammaS in the presence of LPS and GM-CSF augmented the induction of I-A, CD80, CD86, IL-1beta, and IL-12 p40 while inhibiting the expression of IL-10, suggesting that the immunostimulatory activities of purinergic agonists in the skin are mediated at least in part by P2Rs on APCs. In this regard, an LC-like cell line was found to express mRNA for P2X(1), P2X(7), P2Y(1), P2Y(2), P2Y(4), P2Y(9), and P2Y(11) receptors. We suggest that ATP, when released after trauma or infection, may act as an endogenous adjuvant to enhance the immune response, and that P2 agonists may augment the efficacy of vaccines.

Unexpected effects of viral interleukin-10-secreting dendritic cells in vivo: preferential inhibition of TH2 responses

Viral interleukin (IL)-10 (vIL-10) has been widely described as an immunoregulatory cytokine that does not possess the T-cell costimulatory activities of cellular IL-10; it was therefore believed to be a more potent tolerogenic mediator. The immunosuppressive properties of this cytokine are partly attributed to its capacity to render dendritic cells (DCs) unable to undergo full maturation and to activate T cells. We reported here that myeloid DCs retrovirally transduced with vIL-10 had an impaired production of IL-12 and a decreased expression of MHC class II molecules but had minor defects in costimulatory molecule expression and no alteration on CCR5 and CCR7 expression. In mixed leukocyte reaction, vIL-10-transduced C57BL/6 bm12 (MHC class II mismatch) DCs had a reduced capacity to stimulate C57BL/6 wild-type CD4+ T-cell proliferation. We show that bm12 vIL-10-transduced DC administration in CD8-/- C57BL/6 mice promoted IFN-gamma production, down-regulated TH2-type cytokine production, and did not induce skin graft tolerance. These findings suggest that vIL-10-transduced DC may surprisingly facilitate Th1-type inflammatory responses in vivo.

Secreted Immunomodulatory Viral Proteins as Novel Biotherapeutics

Many viruses have learned to evade or subvert the host antiviral immune responses by encoding and expressing immunomodulatory proteins that protect the virus from attack by elements of the innate and acquired immune systems. Some of these viral anti-immune regulators are expressed as secreted proteins that engage specific host immune targets in the extracellular environment, where they exhibit potent anti-immune properties. We review here viral immunomodulatory proteins that have been tested as anti-inflammatory reagents in animal models of disease caused by excessive inflammation or hyperactivated immune pathways. The potential for such viral molecules for the development of novel drugs to treat immune-based or inflammatory disorders is discussed.

Autocrine IL-10 partially prevents differentiation of neonatal dendritic epidermal leukocytes into Langerhans cells

To test whether reduced immune responsiveness in early life may be related to the immaturity of neonatal antigen-presenting cells, we comparatively assessed the phenotypic and functional characteristics of dendritic epidermal leukocytes (DEL) and epidermal Langerhans cells (LC) in newborn (NB) and adult mice, respectively. We report that purified, 3-day-cultured DEL do not acquire the morphology and phenotype typical of LC and are significantly weaker stimulators of naive, allogeneic CD4+ and CD8+ T cells than LC. Freshly isolated DEL are twice as efficient as LC in the uptake of fluorescein isothiocyanate-conjugated tracers but are not able to present these to antigen-specific T cell hybridomas. To clarify the underlying cause, cytokine expression of NB and adult epidermal cells (EC) was examined. We found that DEL express considerable amounts of interleukin (IL)-10, that IL-10 in NB EC supernatants partially inhibits LC maturation, and that DEL-enriched EC from IL-10-/- mice induce stronger primary T cell responses compared with those from IL-10+/+ mice. We conclude that IL-10 is one of the factors preventing maturation and differentiation of DEL into immunocompetent LC in intrauterine life and is at least partly responsible for the poor immune responsiveness of neonates.