Topical Imiquimod Treatment Prevents UV-Light Induced Loss of Contact Hypersensitivity and Immune Tolerance

Toll-Like Receptors and Contact Dermatitis

Contact dermatitis (CD) is a common cutaneous inflammatory condition that affects millions of people worldwide. Xenobiotic agents are frequently encountered in substances used in everyday life, making it difficult to avoid personal and occupational exposure. Toll-like receptors (TLRs) are transmembrane receptors that modulate the innate immune system in response to tissue injury or infection. TLRs play a key role in the pathophysiology of contact dermatitis. TLR signaling is involved in three major forms of CD: protein CD, allergic contact dermatitis (ACD), and irritant CD. Of the 10 TLRs found in humans, three play an important role in ACD. This makes TLRs a useful potential therapeutic target to consider against CD. In this review, we discuss the role of TLRs in CD and summarize current and emerging treatments for CD that target TLRs.

Imiquimod-enhanced immunotherapy with diphencyprone for patients with alopecia areata

Topical immunotherapy with dyphencyprone (DPCP) is widely used in patients with alopecia areata (AA). It can produce a contact dermatitis that is believed to decrease Th1 response, predominant in AA. It has been shown that imiquimod (IMQ), a topical immunomodulator drug, can produce sensitization to DPCP in patients that do not show signs of contact dermatitis when exposed to DPCP. Nevertheless, there is no evidence as to whether it can improve DPCP efficacy in already sensitized patients. We present a series of 9 patients, (7 females [77%] and 2 males [22%]) with a mean age of 38.4 years (range, 19-60 years), successfully sensitized to DPCP, that were treated with a combination of DPCP and IMQ. The mean SALT (Severity of Alopecia Tool) score before adding IMQ was 43.3 (range, 10-60), and the mean number of months of DPCP use prior to the addition of IMQ was 6,8 (range 0-10). After adding IMQ to their DPCP treatment, 77% of the patients had further improvement, with a mean SALT reduction of 13.3 (range, [-50] - 40), and a mean duration of response of 5.2 months. No adverse effects were reported. According to this data, we believe that the combination of DPCP and IMQ can be a promising way of improving the efficacy of contact immunotherapy in AA, and requires further study. This article is protected by copyright. All rights reserved.

Type I Interferons Enhance the Repair of Ultraviolet Radiation-Induced DNA Damage and Regulate Cutaneous Immune Suppression

Type I interferons (IFNs) are important enhancers of immune responses which are downregulated in human cancers, including skin cancer. Solar ultraviolet (UV) B radiation is a proven environmental carcinogen, and its exposure contributes to the high prevalence of skin cancer. The carcinogenic effects of UV light can be attributed to the formation of cyclobutane pyrimidine dimers (CPD) and errors in the repair and replication of DNA. Treatment with a single dose of UVB (100 mJ/cm2) upregulated IFNα and IFNβ in the skin of C57BL/6 mice. IFNα and IFNβ were predominantly produced by CD11b+ cells. In mice lacking the type I IFN receptor 1 (IFNAR1), the repair of CPD following cutaneous exposure to a single dose of UVB (100 mJ/cm2) was decreased. UVB induced the expression of the DNA repair gene xeroderma pigmentosum A (XPA) in wild-type (WT) mice. In contrast, such treatment in IFNAR1 (IFNAR1-/-) mice downregulated XPA. A local UVB regimen consisting of UVB radiation (150 mJ/cm2) for 4 days followed by sensitization with hapten 2,4, dinitrofluorobenzene (DNFB) resulted in significant suppression of immune responses in both WT and IFNAR1-/- mice. However, there were significantly higher CD4+CD25+Foxp3+ regulatory T-cells in the draining lymph nodes of IFNAR1-/- mice in comparison to WT mice. Overall, our studies reveal a previously unknown action of type I IFNs in the repair of photodamage and the prevention of UVB-induced immune suppression.

A Domino Heck Coupling–Cyclization–Dehydrogenative Strategy for the One-Pot Synthesis of Quinolines

An efficient, one-pot, domino synthesis of quinolines via the coupling of iodoanilines with allylic alcohols facilitated by palladium catalysis is described. The overall synthetic process involves an intermolecular Heck coupling between 2-iodoanilines and allylic alcohols, intramolecular condensation of in situ generated ketones with an internal amine functional group, and a dehydrogenation sequence. Notably, this protocol occurs in water as a green solvent. Significantly, the method exhibits broad substrate scope and is applied for the synthesis of deuterated quinolines through a deuterium-exchange process.

Mn(iii)-mediated cascade cyclization of 1-(azidomethyl)-2-isocyanoarenes with organoboronic acids: construction of quinazoline derivatives

A novel and efficient Mn(iii)-mediated oxidative radical cascade reaction of 1-(azidomethyl)-2-isocyanoarenes with organoboronic acids is reported.

Novel cutaneous mediators of chemical allergy

Chemical allergy can manifest into allergic contact dermatitis and asthma and the importance of skin sensitization in both of these diseases is increasingly being recognized. Given the unique characteristics of chemical allergy, coupled with the distinct immunological microenvironment of the skin research is still unraveling the mechanisms through which sensitization and elicitation occur. This review first describes the features of chemical sensitization and the known steps that must occur to develop a chemical allergy. Next, the unique immunological properties of the skin - which may influence chemical sensitization - are highlighted. Additionally, mediators involved with the development of allergy are reviewed, starting with early ones - including the properties of haptens, skin integrity, the microbiome, the inflammasome, and toll-like receptors (TLR). Novel cellular mediators of chemical sensitization are highlighted, including innate lymphoid cells, mast cells, T-helper (T_H) cell subsets, and skin intrinsic populations including γδ T-cells and resident memory T-cells. Finally, this review discusses two epigenetic mechanisms that can influence chemical sensitization, microRNAs and DNA methylation. Overall, this review highlights recent research investigating novel mediators of chemical allergy that are present in the skin. It also emphasizes the need to further explore these mediators to gain a better understanding of what makes a chemical an allergen, and how best to prevent the development of chemical-induced allergic diseases.

TLR4 acts as a death receptor for ultraviolet radiation (UVR) through IRAK-independent and FADD-dependent pathway in macrophages

UVR-induced apoptosis in cutaneous antigen presenting cells (APC) causes systemic immune suppression and is dependent on TLR4/MyD88 signalling, but the apoptotic signalling pathways have not been defined. Macrophages pretreated with lipopolysaccharide (LPS) were unresponsive to subsequent LPS treatment, however, but were susceptible to UVR-induced apoptosis. Macrophage survival and apoptotic events after UVR were also unaffected by treatment with TLR4 antagonists, a blocking IgG or a TLR4 analog antagonist, suggesting that UVR cell death is independent of a soluble ligand. After UVR, IRAK4^KDKI (catalytically inactive IRAK4) and wild-type (WT) macrophages show equivalent levels of survival, as measured by MTT assay, and apoptosis, as measured by cleaved caspase-3. Furthermore, in macrophages from both mice, UVR activated caspase-8 and PARP, while inactivating Rip3. This finding is supported by a lack of IRAK1 degradation after UVR, compared to treatment with TLR2 or TLR4 agonists. UVR induced association of MyD88 with FADD, an extrinsic apoptotic pathway protein, but not IRAK4. UVR-induced migration of FADD to the cell membrane of WT macrophages, but not MyD88^-/- macrophages, was observed (confocal microscopy). Co-immunoprecipitation using an epitope-tagged MyD88 revealed that FADD, but not TRADD, was recruited to MyD88 within 30 minutes of UVR exposure. UVR engages TLR4/MyD88 as a death signalling complex, rather than the classical inflammatory signalling pathway triggered by PAMP recognition of TLR4. These studies provide the rationale for the future development of topical TLR4 modulating therapies to interfere with this UVB-mediated apoptosis and the associated negative consequences of immune suppression.

Antibiotic-Induced Depletion of Murine Microbiota Induces Mild Inflammation and Changes in Toll-Like Receptor Patterns and Intestinal Motility

We examine the impact of changes in microbiota induced by antibiotics on intestinal motility, gut inflammatory response, and the function and expression of toll-like receptors (TLRs). Alterations in mice intestinal microbiota were induced by antibiotics and evaluated by q-PCR and DGGE analysis. Macroscopic and microscopic assessments of the intestine were performed in control and antibiotic-treated mice. TLR expression was determined in the intestine by q-RT-PCR. Fecal parameter measurements, intestinal transit, and muscle contractility studies were performed to evaluate alterations in intestinal motility. Antibiotics reduced the total bacterial quantity 1000-fold, and diversity was highly affected by treatment. Mice with microbiota depletion had less Peyer's patches, enlarged ceca, and mild gut inflammation. Treatment with antibiotics increased the expression of TLR4, TLR5, and TLR9 in the ileum and TLR3, TLR4, TLR6, TLR7, and TLR8 in the colon, and it reduced the expression of TLR2, TLR3, and TLR6 in the ileum and TLR2 and TLR9 in the colon. Antibiotics decreased fecal output, delayed the whole gut and colonic transit, and reduced the spontaneous contractions and the response to acetylcholine (ACh) in the ileum and colon. Activation of TLR4 by lipopolysaccharide (LPS) reverted the reduction of the spontaneous contractions induced by antibiotics in the ileum. Activation of TLR4 by LPS and TLR5 by flagellin reduced the response to ACh in the ileum in control mice. Our results confirm the role of the microbiota in the regulation of TLRs expression and shed light on the microbiota connection to motor intestinal alterations.

Ultraviolet radiation signaling through TLR4/MyD88 constrains DNA repair and plays a role in cutaneous immunosuppression

UV radiation (UVR) induces DNA damage, leading to the accumulation of mutations in epidermal keratinocytes and immunosuppression, which contribute to the development of nonmelanoma skin cancer. We reported previously that the TLR4-MyD88 signaling axis is necessary for UV-induced apoptosis. In the dinitrofluorobenzene contact hypersensitivity model, UV-irradiated MyD88-deficient (MyD88(-/-)) C57BL/6 mice had intact ear swelling, exaggerated inflammation, and higher levels of dinitrofluorobenzene-specific IgG2a compared with wild-type (WT) mice. Even with normal UV-induced, dendritic cell migration, DNA damage in the local lymph nodes was less pronounced in MyD88(-/-) mice compared with WT mice. Cultured, UV-irradiated WT APCs showed cleavage (inactivation) of the DNA damage-recognition molecule PARP, whereas PARP persisted in MyD88(-/-) and TLR4(-/-) APCs. Epidermal DNA from in vivo UV-irradiated MyD88(-/-) mice had an increased resolution rate of cyclobutane pyrimidine dimers. Both in vitro treatment of MyD88(-/-) APCs with and intradermal in vivo injections of PARP inhibitor, PJ-34, caused WT-level cyclobutane pyrimidine dimer repair. Lymphoblasts deficient in DNA repair (derived from a xeroderma pigmentosum group A patient) failed to augment DNA repair after MyD88 knockdown after UVR, in contrast to lymphoblasts from a healthy control. These data suggest that interference with the TLR4/MyD88 pathway may be a useful tool in promoting DNA repair and maintaining immune responses following UVR-induced damage.

Human in vitro skin organ culture as a model system for evaluating DNA repair

BACKGROUND

UV-exposures result in accumulation of genetic lesions that facilitate the development of skin cancer. Numerous pharmacologic agents are currently under development to both inhibit formation of DNA lesions and enhance repair. Drugs must be evaluated in vitro, currently performed in cell culture systems, before being tested on humans. Current systems do not account for the architecture and diverse cellularity of intact human skin.

OBJECTIVE

To establish a novel, functionally viable, and reproducible in vitro skin organ culture system for studying the effects of various pharmacologic agents on DNA repair.

METHODS

Human skin was obtained from neonatal foreskins. Intact skin punches derived from foreskins were cultured in vitro prior to exposure to UV-irradiation, and evaluated for DNA-damage using a DNA dot blot. Serial skin biopsies were obtained from patients with actinic keratoses treated with topical imiquimod. Expression of immune-stimulating and DNA repair genes was evaluated in ex vivo and in vitro samples.

RESULTS

DNA dot blots revealed active repair of UV induced lesions in our in vitro skin organ culture. The photo-protective effect of sunscreen was detected, while imiquimod treatment did not enhance DNA repair in vitro. The DNA repair molecules XPA and XPF were up-regulated in the skin of imiquimod treated patients with actinic keratoses and imiquimod treated bone marrow-derived cell lines, but not keratinocytes.

CONCLUSION

Our in vitro human skin organ culture model detected repair of UV-induced DNA lesions, and may be easily adapted to investigate various photo-protective drugs intended to prevent or treat skin cancer.

IL-9 regulates allergen-specific Th1 responses in allergic contact dermatitis

The cytokine IL-9, derived primarily from T-helper 9 (Th9) lymphocytes, promotes expansion of the Th2 subset and is implicated in the mechanisms of allergic asthma. We hypothesize that IL-9 also has a role in human allergic contact dermatitis (ACD). To investigate this hypothesis, skin biopsy specimens of positive patch-test sites from non-atopic patients were assayed using quantitative PCR and immunohistochemistry. The cytokines IFN-γ, IL-4, IL-17A, IL-9, and PU.1, a Th9 associated transcription factor, were elevated when compared with paired normal skin. Immunohistochemistry on ACD skin biopsies identified PU.1+ CD3+ and PU.1+ CD4+ cells, consistent with Th9 lymphocytes, in the inflammatory infiltrate. Peripheral blood mononuclear cells from nickel-allergic patients, but not nonallergic controls, show significant IL-9 production in response to nickel. Blocking studies with mAbs to HLA-DR (but not HLA-A, -B, -C) or chloroquine significantly reduced this nickel-specific IL-9 production. In addition, blockade of IL-9 or IL-4 enhanced allergen-specific IFN-γ production. A contact hypersensitivity model using IL-9(-/-) mice shows enhanced Th1 lymphocyte immune responses, when compared with wild-type mice, consistent with our human in vitro data. This study demonstrates that IL-9, through its direct effects on Th1 and ability to promote IL-4 secretion, has a regulatory role for Th1 lymphocytes in ACD.

Toll-like receptor-4 deficiency enhances repair of UVR-induced cutaneous DNA damage by nucleotide excision repair mechanism

UVB-induced DNA damage plays a critical role in development of photoimmunosuppression. The purpose of this study was to determine whether repair of UVB-induced DNA damage is regulated by Toll-like receptor-4 (TLR4). When TLR4 gene knockout (TLR4^-/-) and TLR4 competent (TLR4^+/+) mice were subjected to 90 mJ/cm² UVB radiation locally, DNA damage in the form of CPD, were repaired more efficiently in the skin and bone marrow dendritic cells (BMDC) of TLR4^-/- mice in comparison to TLR4^+/+ mice. Expression of DNA repair gene XPA (Xeroderma pigmentosum complementation group A) was significantly lower in skin and BMDC of TLR4^+/+ mice than TLR4^-/- mice after UVB exposure. When cytokine levels were compared in these strains after UVB exposure, BMDC from UV-irradiated TLR4^-/- mice produced significantly more interleukin (IL)-12 and IL-23 cytokines (p<0.05) than BMDC from TLR4^+/+ mice. Addition of anti-IL-12 and anti-IL-23 antibodies to BMDC of TLR4^-/- mice (before UVB exposure) inhibited repair of CPD, with a concomitant decrease in XPA expression. Addition of TLR4 agonist to TLR4^+/+ BMDC cultures decreased XPA expression and inhibited CPD repair. Thus, strategies to inhibit TLR4 may allow for immunopreventive and immunotherapeutic approaches for managing UVB-induced cutaneous DNA damage and skin cancer.

TLR signaling and DNA repair: are they associated?

Toll-like receptor (TLR) signaling is a well-characterized, innate immune cellular defense mechanism used to detect and respond to pathogen-associated molecular patterns (PAMPs). TLR signaling is highly conserved and has evolved to have both extracellular and endosomal receptors that recognize PAMPs from a wide range of microbial pathogens. Recent literature has emerged to show that activation of TLRs not only leads to the upregulation of cellular defense mechanisms, but also results in upregulation of DNA repair genes and increased functional DNA repair. Endosomal TLR agonists result in increased survival and repair after both ionizing and UV radiation, suggesting that the repair pathways for single- and double-strand breaks are affected. This review brings together these and other experimental findings to examine how DNA repair pathways may be linked to TLR signaling. Also discussed are the varied outcomes and related physiological implications that increased DNA repair after injury might have.

Imiquimod-induced TLR7 signaling enhances repair of DNA damage induced by ultraviolet light in bone marrow-derived cells

Imiquimod is a TLR7/8 agonist that has anticancer therapeutic efficacy in the treatment of precancerous skin lesions and certain nonmelanoma skin cancers. To test our hypothesis that imiquimod enhances DNA repair as a mechanism for its anticancer activity, the nucleotide excision repair genes were studied in bone marrow-derived cells. Imiquimod enhanced the expression of xeroderma pigmentosum (XP) A and other DNA repair genes (quantitative real-time PCR analysis) and resulted in an increased nuclear localization of the DNA repair enzyme XPA. This was dependent on MyD88, as bone marrow-derived cells from MyD88(-/-) mice did not increase XPA gene expression and did not enhance the survival of MyD88(-/-)-derived bone marrow-derived cells after UV B exposure as was observed in bone marrow-derived cells from MyD88(+/+) mice. Imiquimod also enhanced DNA repair of UV light (UVL)-irradiated gene expression constructs and accelerated the resolution of cyclobutane pyrimidine dimers after UVL exposures in P388 and XS52. Lastly, topical treatment of mouse skin with 5% imiquimod cream prior to UVL irradiation resulted in a decrease in the number of cyclobutane pyridimine dimer-positive APC that were found in local lymph nodes 24 h after UVL irradiation in both wild-type and IL-12 gene-targeted mice. In total, these data support the idea that TLR7 agonists such as imiquimod enhance DNA repair in bone marrow-derived cells. This property is likely to be an important mechanism for its anticancer effects because it protects cutaneous APC from the deleterious effects of UVL.

Synthesis of 2,4-Diarylquinolines: Nickel-Catalysed Ligand-Free Cross-Couplings of 4-Chloro-2-Arylquinolines with Arylmagnesium Halides in 2-Methyltetrahydrofuran

A ligand-free and room temperature protocol for the synthesis of 2,4-diarylquinolines is described. Treatment of 4-chloro-2-arylquinolines with arylmagnesium halides in the presence of a catalytic amount of nickel(II) chloride without ligands in 2-methyltetrahydrofuran (2-MeTHF) afforded the corresponding cross-coupling products in good yields.

Regulation of ultraviolet radiation induced cutaneous photoimmunosuppression by toll-like receptor-4

UVB radiation is a potent immunosuppressive agent that inhibits cell-mediated immune responses. The mechanisms by which UVB radiation influences cell-mediated immune responses have been the subject of extensive investigation. However, the role of innate immunity on photoimmunological processes has received little attention. The purpose of this study was to determine whether Toll-like receptor-4 (TLR4) contributed to UV-induced suppression of contact hypersensitivity (CHS) responses. TLR4⁻/⁻ and wild type C57BL/6 (TLR4+/+) mice were subjected to a local UVB immunosuppression regimen consisting of 100 mJ/cm² UVB radiation followed by sensitization with the hapten DNFB. Wild type TLR4+/+ mice exhibited significant suppression of contact hypersensitivity response, whereas TLR4⁻/⁻ developed significantly less suppression. The suppression in wild type TLR4+/+ mice could be adoptively transferred to naïve syngeneic recipients. Moreover, there were significantly fewer Foxp3 expressing CD4+CD25+ regulatory T-cells in the draining lymph nodes of UV-irradiated TLR4⁻/⁻ mice than TLR4+/+ mice. When cytokine levels were compared in these two strains after UVB exposure, T-cells from TLR4+/+ mice produced higher levels of IL-10 and TGF-β and lower levels of IFN-γ and IL-17. Strategies to inhibit TLR4 may allow us to develop immunopreventive and immunotherapeutic approaches for management of UVB induced cutaneous immunosuppression.

Differential roles of T-cell subsets in regulation of ultraviolet radiation induced cutaneous photocarcinogenesis

Ultraviolet (UV) radiation, in particular the midwavelength range (UVB; 290-320 nm), is one of the most significant risk factors for the development of nonmelanoma skin cancer. UVB radiation-induced immunosuppression, which occurs in both humans and laboratory animals, contributes to their pathogenesis. However, there are conflicting reports on the relative role of CD4(+) and CD8(+) T cells in UVB induced skin cancer. The purpose of this study was to delineate the contribution of these two cell subpopulations to UVB induced immunosuppression and tumor development using C3H/HeN (WT), CD4 knockout (CD4(-/-) ) and CD8 knockout (CD8(-/-) ) mice. We observed that UVB induced skin carcinogenesis was retarded in terms of number of tumors per group, tumor volume and percentage of mice with tumors, in mice deficient in CD4(+) T cells compared with wild-type mice, whereas significantly greater (P < 0.05) numbers of tumors occurred in CD8(-/-) mice. These results indicate that, CD4(+) T cells promote tumor development while CD8(+) T cells have the opposite effect. Further, we found that CD4(+) T cells from tumor-bearing mice produced interleukin (IL)-4, IL-10, and IL-17 whereas CD8(+) T cells produced interferon-γ. Manipulation of T-cell subpopulations that are induced by UVB radiation could be a means of preventing skin cancers caused by this agent.

UV exposure boosts transcutaneous immunization and improves tumor immunity: cytotoxic T-cell priming through the skin

Immunologic approaches to combat cancer aim at the induction of tumor-reactive immune responses to achieve long-term protection. In this context, we recently developed a transcutaneous immunization (TCI) method using the Toll-like receptor (TLR) 7 agonist imiquimod and a peptide epitope. Application onto intact skin induces potent cytotoxic T lymphocyte (CTL) responses and protection against transplanted tumors. The purpose of this study was to explore the effects of UV irradiation on imiquimod-based TCI. Here we show that skin exposure to low-dose UV light before TCI with imiquimod strongly boosts specific CTL responses leading to memory formation and enhanced tumor protection. Toward the mechanisms, we show that the activation of bone-marrow-derived dermal dendritic cells (DCs), but not Langerin-expressing DCs, is responsible for enhanced CTL activation. We describe an optimized TCI method that mediates enhanced CTL and antitumor responses by a DC- and TLR-dependent mechanism. These data may provide the basis for the future development of advanced vaccination protocols against tumors and persistent virus infections.

Efforts to counteract locally the effects of systemic immunosupression: a review on the use of imiquimod, a topical immunostimulator in organ transplant recipients

The potent systemic immunosuppression therapy necessary to sustain a life-saving solid organ transplant is associated with an increased incidence of various infections including human papillomavirus infection and skin cancers in organ transplant recipients. Imiquimod, a topical agent that functions through local induction of a specific anti-viral or anti-tumor immune response, appears to be a promising therapeutic option that could potentially counteract in situ the effects of systemic immunosupression in this vulnerable group. Up-to-date studies using this local immune-response modifier in transplanted patients have yielded reassuring and encouraging results regarding its safety and efficacy in this population. However, in order to establish the use of imiquimod as a standard treatment option for organ transplant recipients, additional research and clinical trials are required.

T regulatory cells in contact hypersensitivity

PURPOSE OF REVIEW

The review summarizes the recent investigations focused on T regulatory cells in hapten diseases.

RECENT FINDINGS

Multiple mechanisms ensure tolerance to small chemicals penetrating the skin. Among these, specific T regulatory cells play a major role in controlling harmful immune responses to environmental antigens. Most of the T regulatory cells involved in this process belongs to the CD4 subset and suppress hapten-specific immune response through the release of IL-10 and through direct interaction with effector T cells, blocking their function.

SUMMARY

Methods for in-vitro and in-vivo expansion of specific T regulatory cells may represent an innovative approach for the cure of contact hypersensitivity.

Imiquimod inhibits the differentiation but enhances the maturation of human monocyte-derived dendritic cells

Imiquimod is a topically used immune response modifier effective in the treatment of genital warts caused by HPV. Its therapeutic effects are believed to be the release of proinflammatory cytokines from the monocyte-macrophage lineage resulting in a cascade of events abating the HPV replication. Dendritic cell maturation and activation have also been found to be induced by imiquimod. We hypothesized that imiquimod may promote the development of DC at all levels of their life cycle. In this study, in vitro cultured monocyte-derived dendritic cells (MoDC) were used to evaluate the effect of imiquimod regarding the modulation of DC differentiation, terminal maturation and their function by phenotypic cell surface molecules expression, cytokine secretion and T cell stimulation in allogeneic system. We demonstrate that imiquimod exerts differential effects on DC biology at different stages of DC development. It inhibits the differentiation of DC, which may indicate a more potent antigen uptake activity. DC maturation is induced by imiquimod with an enhanced antigen presenting activity and IL-12 production. These evidence might be relevant with the clinically proven effectiveness of imiquimod in the treatment of genital warts.

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.

Topical imiquimod: a review of its use in the management of anogenital warts, actinic keratoses, basal cell carcinoma and other skin lesions

Topical imiquimod 5% cream (Aldara) is an immune response modulator that is indicated for the treatment of external anogenital warts, superficial basal cell carcinoma and actinic keratoses. The cream is applied two to five times per week for varying periods, depending on the indication. Topical imiquimod cream has also been evaluated in the treatment of several other skin conditions. Immunomodulatory therapy with topical imiquimod 5% is an effective option for the approved indications. The drug appears to be relatively well tolerated, with the option of breaks from treatment as required for local skin reactions (which are common). Systemic reactions have been reported. Treatment of human papillomavirus- and UV-associated skin lesions with topical imiquimod offers a noninvasive, tissue-sparing alternative to ablative treatment options. However, well designed trials of the sustained, long-term efficacy and tolerability of topical imiquimod versus those of common treatment approaches including surgery and other topical alternatives are required before the place of the drug in the management of these lesions can be finalised. Nonetheless, while other treatments for anogenital warts, superficial basal cell carcinoma or actinic keratoses are available, the advantages of self treatment linked with the demonstrated efficacy of topical imiquimod offer an attractive alternative for many patients.

Does imiquimod histologically rejuvenate ultraviolet radiation-damaged skin?

BACKGROUND

Imiquimod (IMI) 5% is believed by some to result in an improved cosmetic appearance of chronically ultraviolet radiation (UV)-damaged skin.

OBJECTIVE

The objective was to determine what histologic and immunohistologic changes were present in actinically damaged skin after treatment with IMI.

METHODS AND MATERIALS

Pre- and posttherapy biopsies of 12 patients with histories of actinic keratoses were evaluated with routine histology and immunohistochemical stains including p53, p63, proliferating cell nuclear antigen (PCNA), c-kit, and Factor XIIIa.

RESULTS

After IMI therapy there was less compact hyperkeratosis, a more uniform rete ridge pattern with a more ordered proliferation of the epidermis, and a decrease in sun-damaged melanocytes. The papillary dermis showed a more uniform cellularity, and there was increased cellularity within the area of solar elastosis. After therapy, staining for p53, p63, and PCNA was decreased within the epidermis; staining for c-kit was decreased but more uniform in the basal cell; and Factor XIIIa expression was increased within the papillary dermis with a more ordered pattern of staining.

CONCLUSION

These morphologic and immunohistochemical patterns may explain some of the improvement in overall skin appearance after IMI therapy and may be related to the spectrum of signaling pathways induced by the imidazoquinolines.

Lipopolysaccharide promotes and augments metal allergies in mice, dependent on innate immunity and histidine decarboxylase

BACKGROUND

Few adequate murine models exist for metal allergies, it being especially difficult to induce Ni allergy in mice.

OBJECTIVE

We examined the effect of lipopolysaccharide (LPS) on allergies to Ni and other metals in mice.

METHODS

Ten days after sensitization with a metal salt and LPS, the ears were challenged with the same metal salt.

RESULTS

LPS+NiCl(2) (1 mM) was effective at sensitizing mice to Ni, LPS being effective at very low concentrations whether injected intradermally or intraperitoneally. The ear-swelling response to Ni was more severe and more rapid in C57BL/6 mice than in BALB/c mice. In mast-cell-deficient mice, TNF-alpha-deficient mice, and interestingly even in nude (T cell deficient) mice, NiCl(2)+LPS induced a Ni allergy similar in degree to that in the respective control mice, but it induced Ni allergy only weakly in TLR4-mutant mice, macrophage-depleted mice, and IL-1-deficient mice. The activity of the histamine-forming enzyme histidine decarboxylase (HDC) in the ears increased in parallel with ear swelling, and HDC-deficient mice were resistant to ear swelling. Challenge with NiCl(2)+LPS augmented ear swelling (vs. NiCl(2) alone). LPS induced effective sensitization to other metals (Cr, Co, Pd, or Ag).

CONCLUSIONS

These results indicate that in mice, LPS is a very important inducer of metal allergies, and potently promotes them (dependent on both innate immunity and HDC induction in cells other than mast cells). We discussed the idea that the bacterial environment is important for the establishment of metal allergies and for their provocation, and that the current thinking (including the contribution of T cells) should be reappraised in future studies.