Three decades of psoriasis research: where has it led us?

Caspase 1/11 Deficiency or Pharmacological Inhibition Mitigates Psoriasis-Like Phenotype in Mice

Inflammatory caspases, activated within the inflammasome, are responsible for the maturation and secretion of IL-1β/IL-18. Although their expression in psoriasis was shown several years ago, little is known about the role of inflammatory caspases in the context of psoriasis. Here, we confirmed that caspases 1, 4, and 5 are activated in lesional skin from psoriasis patients. We showed in three psoriasis-like models that inflammatory caspases are activated, and accordingly, caspase 1/11 invalidation or pharmacological inhibition by Ac-YVAD-CMK (i.e., Ac-Tyr-Val-Ala-Asp-chloromethylketone) injection induced a decrease in ear thickness, erythema, scaling, inflammatory cytokine expression, and immune cell infiltration in mice. We observed that keratinocytes were primed to secrete IL-1β when cultured in conditions mimicking psoriasis. Generation of chimeric mice by bone marrow transplantation was carried out to decipher the respective contribution of keratinocytes and/or immune cells in the activation of inflammatory caspases during psoriasis-like inflammatory response. Our data showed that the presence of caspase 1/11 in the immune system is sufficient for a fully inflammatory response, whereas the absence of caspase 1/11 in keratinocytes/fibroblasts had no impact. In summary, our study indicates that inflammatory caspases activated in immune cells are implicated in psoriasis pathogenesis.

Trends in Type of Original Psoriasis Publications by Decade, 1960 to 2010

CONTEXT

Research investigating psoriasis has spanned decades, and as our understanding of the disease has evolved, the focus of publications has changed.

OBJECTIVE

We sought to characterize the trends in original psoriasis-related research from 1960 to 2010 chronologically by decade.

METHODS

A literature review was performed using the keyword psoriasis in the MEDLINE database. All original psoriasis-related articles published at the beginning of each decade were searched and categorized by study type and topic.

MAIN OUTCOME MEASURE

Number of articles per topic.

RESULTS

A total of 869 original psoriasis-related articles were found. The number of publications increased 18 fold over 5 decades. The immunology and pathogenesis of psoriasis was the most frequently researched topic (36%), and retrospective studies were the most common study type (37%). Recent highly published topics included biologic therapy, genetics, and psoriasis-associated cardiovascular disease.

CONCLUSION

Original psoriasis-related publications have grown substantially since 1960. Basic science research into the immunology and pathogenesis has been and continues to be the mainstay of psoriasis research. Recent research trends suggest the focus has expanded to topics such as psoriasis-associated cardiovascular disease, genetics, and biologic therapy.

Safety and efficacy of kunzea oil-containing formulations for the management of psoriasis: a randomized, controlled trial

WHAT IS KNOWN AND OBJECTIVE

Anecdotally, topical kunzea oil has been used to treat various skin conditions, including psoriasis and eczema, with good results. This study compared the clinical efficacy of kunzea oil (20%)-containing formulations in mild to moderate psoriasis.

METHODS

A randomized, comparative, double-blind, 8-week study was undertaken. Thirty patients (age range: 25-74 years and mean ± SD: 52·8 ± 13·6 years) with mild to moderate psoriasis (affecting at least 10% of one or more body regions: arms, head, legs and trunk) randomly received ointment and/or scalp lotion containing 20% kunzea oil (test group) or control medications not containing kunzea oil (control group). Formulations in both treatment arms also contained 5% liquor carbonis detergens (LCD) and 3% salicylic acid. The clinical responses to the test and control formulations were evaluated using the Psoriasis Area and Severity Index (PASI).

RESULTS AND DISCUSSION

After 8 weeks of treatment, both test and control groups demonstrated a significant (P < 0·05) improvement in PASI scores. Subjects in the test group had a decrease in mean±SD PASI score from 12·7 ± 7·9 to 6·7 ± 7·2, whereas the control group showed a decrease in PASI score from 8·1 ± 4·6 to 3·5 ± 4·7. Comparative efficacy analysis between the test and control groups did not reveal any significant difference (P > 0·05).

WHAT IS NEW AND CONCLUSIONS

The inclusion of kunzea oil made no difference to the efficacy of topical formulations containing LCD and salicylic acid for the treatment of psoriasis.

The antiangiogenic insulin receptor substrate-1 antisense oligonucleotide aganirsen impairs AU-rich mRNA stability by reducing 14-3-3β-tristetraprolin protein complex, reducing inflammation and psoriatic lesion size in patients

Increased inflammation and aberrant angiogenesis underlie psoriasis. Here, we report that the inhibition of insulin receptor substrate-1 (IRS-1) expression with aganirsen resulted in a dose-dependent reduction (P < 0.0001) in IRS-1 protein in the cytoplasm, while IRS-1 protein remained quantitatively unchanged in the perinuclear environment. Aganirsen induced a dose-dependent increase in serine-phosphorylated IRS-1 in the soluble perinuclear-nuclear fraction, inducing IRS-1-14-3-3β protein association (P < 0.001), thereby impairing 14-3-3β-tristetraprolin protein complex and AU-rich mRNA's stability (P < 0.001). Accordingly, aganirsen inhibited (P < 0.001) in vitro the expression of interleukin-8 (IL-8), IL-12, IL-22, and tumor necrosis factor alpha (TNFα), four inflammatory mediators containing mRNA with AU-rich regions. To demonstrate the clinical relevance of this pathway, we tested the efficacy of aganirsen by topical application in a pilot, double-blind, randomized, dose-ranging study in 12 psoriatic human patients. After 6 weeks of treatment, least square mean differences with placebo were -38.9% (95% confidence interval, -75.8 to -2.0%) and -37.4% (-74.3 to -0.5%) at the doses of 0.86 and 1.72 mg/g, respectively. Lesion size reduction was associated with reduced expression of IRS-1 (P < 0.01), TNFα (P < 0.0001), and vascular endothelial growth factor (P < 0.01); reduced keratinocyte proliferation (P < 0.01); and the restoration (P < 0.02) of normal levels of infiltrating CD4(+) and CD3(+) lymphocytes in psoriatic skin lesions. These results suggest that aganirsen is a first-in-class of a new generation of antiangiogenic medicines combining anti-inflammatory activities. Aganirsen-induced downregulation of inflammatory mediators characterized by AU-rich mRNA likely underlies its beneficial clinical outcome in psoriasis. These results justify further large-scale clinical studies to establish the dose of aganirsen and its long-term efficacy in psoriasis.

Therapeutic opportunities of the IL-22-IL-22R1 system

Interleukin-22 (IL-22) is a key effector molecule that is produced by activated T cells, including T helper 22 (TH22) cells, TH17 cells and TH1 cells, as well as subsets of innate lymphoid cells. Although IL-22 can act synergistically with IL-17 or tumour necrosis factor, some important functions of IL-22 are unique to this cytokine. Data obtained over the past few years indicate that the IL-22-IL-22 receptor subunit 1 (IL-22R1) system has a high potential clinical relevance in psoriasis, ulcerative colitis, graft-versus-host disease, certain infections and tumours, as well as in liver and pancreas damage. This Review highlights current knowledge of the biology of the IL-22-IL-22R1 system, its role in inflammation, tissue protection, regeneration and antimicrobial defence, as well as the positive and potentially negative consequences of its therapeutic modulation.

Isothiocyanates inhibit psoriasis-related proinflammatory factors in human skin

OBJECTIVE

4-Methylthiobutylisothiocyanate (MTBI), the main rocket (Eruca sativa) seed isothiocyanate (ITC), and its oxidized form, sulforaphane (SFN), were assessed for their potential effects on psoriasis-related factors.

METHODS

MTBI and SFN were evaluated for their effect on mRNA expression and cytokine secretion in vitro in human monocytes and macrophage-like cells and ex vivo in topically treated inflamed human skin. In addition, they were assayed in vivo for morphological changes in topically treated psoriasiform human skin in severe-combined immunodeficient (SCID) mice.

RESULTS

MTBI and SFN contributed to the prevention of inflammation development and reduced ongoing inflammation by downregulating lipopolysaccharide (LPS)-induced mRNA expression of the psoriasis-related cytokines, interleukin (IL)-12/23p40 (25-58 %), tumor necrosis factor (TNF)-α (15-37 %) and IL-6 (25-71 %), in human macrophage-like cells. In monocytes, they tended to act additively on cytokine mRNA and reduced IL-12/23p40 (51 %) secretion. In an ex-vivo inflamed human skin organ culture, MTBI (1 μg/ml) reduced the secretion of IL-1 (39 %) and IL-6 (32 %). Moreover, 2/8 and 3/8 of the MTBI- and SFN-treated psoriasiform SCID mice, respectively, recovered partially or entirely from the psoriasiform process.

CONCLUSIONS

Results from these models indicate the potential of rocket seed ITCs as biological agents in the therapy of psoriasis and inflammation-related skin diseases.

Cutaneous microdialysis: cytokine evidence for altered innate reactivity in the skin of psoriasis patients?

Cutaneous microdialysis demonstrates cytokine production in living human skin. In the present study, microdialysis samples taken from uninvolved and lesional skin in three test subjects with psoriasis over 24 h have been investigated for cytokine content with a bead-based multiplex immunoassay from Luminex. Concentration curves for a set of Th1/Th2 and pro-inflammatory cytokines measured differed from a reference group of ten subjects without psoriasis. The time to return to near baseline values after innate insertion reactivity is between 9 and 16 h. Post-equilibration levels (17-24 h) for the three main cytokines elevated in the reference group were differentially elevated outside the range of the reference group for interleukin-1β (IL1β) and IL8 but not so for IL6. Two further cytokines, granulocyte-macrophage colony-stimulating factor and tumor necrosis factor-α not generally elevated in the reference group, showed elevated values in the test subjects. Multivariate time series analysis (chemometry) showed that cytokine patterns for the individual test subjects often fell outside the 99% confidence intervals of a model generated from the reference group. In a clinical research situation, cutaneous microdialysis is feasible, gives generally higher cytokine levels than in the blood and generates interpretable data on an individual's reactivity compared with a reference group. This may well prove useful in delineation of pathogenetic issues, selection of appropriate therapy and monitoring of subsequent response in inflammatory dermatoses such as psoriasis.

Research in practice: IL-22 and IL-20: significance for epithelial homeostasis and psoriasis pathogenesis

Psoriasis vulgaris is a frequent, chronically relapsing, immune-mediated, systemic disease with characteristic skin changes. Despite the importance of this disease there are currently limited therapeutic options indicating a need for effective, long-lasting treatment strategies with few side effects. The most recent discoveries regarding psoriasis pathogenesis, particularly our results regarding two cytokines - IL-22 and IL-20 - could prove to be the foundation for such therapies. Whereas IL-22 is mainly produced by activated T-cell sub-populations (Th22, Th1, Th17), monocytes, dendritic cells and keratinocytes produce IL-20. Blood and lesional skin samples from psoriasis patients demonstrate high levels of IL-22 and IL-20. Interestingly, both cytokines act principally on keratinocytes and do not impact the immune system. Similar to the changes in the psoriasis epidermis these cytokines inhibit the terminal differentiation of keratinocytes although they simultaneously increase their innate defense, mobility, and the production of some chemokines. Some IL-22 effects are amplified by TNF-α, IL-17, and IFN-α. IL-22/IL-20 lends the reconstructed epidermis a psoriasis-like appearance with acanthosis, hypogranularity, and hyperkeratosis. In addition, mice that constitutively express high levels of IL-22 or IL-20 demonstrate a psoriasis-like appearance. A therapy counteracting IL-22 and IL-20 would be an innovative treatment with the potential for few side effects that would act on the final phase of psoriasis pathogenesis.

Marked differences in Betapapillomavirus DNA and antibody prevalence between patients with psoriasis and those with atopic dermatitis

BACKGROUND

Recent studies revealed that Betapapillomavirus (betaPV) infections are highly prevalent. Skin diseases such as psoriasis, characterized by keratinocyte hyperproliferation, and atopic dermatitis (AD), dominated by cutaneous inflammation, might have an impact on viral life cycle and immune response induction.

OBJECTIVES

To investigate whether betaPV infection is different in psoriasis and AD.

METHODS

Twenty-seven patients with psoriasis and 17 with AD were included for betaPV genotyping using eyebrow hairs, and for seroresponse determination.

RESULTS

BetaPV DNA was found significantly more often in patients with psoriasis than in those with AD (100% vs. 81%, P=0·022) and the mean number of betaPV types was higher (4·8 vs. 2·1 types, P=0·002). In contrast, the seroprevalence in patients with AD was significantly higher compared with that in patients with psoriasis (88% vs. 56%, P=0·023). Type-specific concordance of serological response to the betaPV type detected in eyebrow hairs was 27% in patients with psoriasis and 47% in those with AD (P=0·019).

CONCLUSIONS

We speculate that the condition of the skin and the immunological state of the patients have an important impact on the life cycle of betaPV.

Interleukin (IL)-22, IL-17, IL-23, IL-8, vascular endothelial growth factor and tumour necrosis factor-α levels in patients with psoriasis before, during and after psoralen-ultraviolet A and narrowband ultraviolet B therapy

BACKGROUND

Several cross-sectional studies have shown that different cytokines and growth factors are enhanced in psoriasis.

OBJECTIVES

We aimed to understand the role/relation of interleukin (IL)-22, IL-17, IL-23, IL-8, vascular endothelial growth factor (VEGF) and tumour necrosis factor (TNF)-α in psoriasis vulgaris, addressing their levels and changes before, during and after psoralen-ultraviolet A (PUVA) and narrowband ultraviolet B (NB-UVB) treatment.

METHODS

A cross-sectional and a longitudinal study (n = 34) - before (T0) and at 3 (T3), 6 (T6) and 12 (T12) weeks of NB-UVB and PUVA therapy - were performed; 17 patients started NB-UVB and 17 PUVA, and IL-22, IL-17, IL-23, IL-8, TNF-α and VEGF levels were evaluated.

RESULTS

At T0, compared with controls (n = 20), all the parameters were significantly higher in patients, except for TNF-α. Both NB-UVB and PUVA treatment gave, at T3, a significant decrease in TNF-α and IL-23; IL-22 and IL-17 decreased significantly at T6; all parameters and Psoriasis Area and Severity Index decreased significantly at T12. However, in both groups, at T12, VEGF was still significantly higher than control.

CONCLUSIONS

Psoriasis seems to be a complex disease in which the cytokine network is disturbed, namely in levels of IL-22, IL-17, IL-23, IL-8, TNF-α and VEGF. NB-UVB and PUVA follow-up studies suggested that the reduction in the IL-23/Th17 axis might be important in the pathogenic mechanisms of psoriasis. Further follow-up studies of patients with psoriasis treated with these and other therapies could be very helpful for the understanding of the disturbance in the cytokine network in psoriasis and indirectly in its pathogenesis.

IL-10 family of cytokines

In 2001, six immune mediators (IL-10, IL-19, IL-20, IL-22, IL-24, and IL-26) were grouped into the so-called IL-10 family of cytokines based on their similarities with respect to the structure and location of their encoding genes, their primary and secondary protein structures, and the receptor complexes used. Surprisingly, despite all these similarities, IL-10 family members possess different biological functions. The currently known facts regarding the biological effects of these six immune mediators give the impression that at least IL-10, IL-20, and IL-22 play an important role in the pathogenesis of some chronic inflammatory diseases. This review provides an overview of the most important and common aspects of the IL-10 family members.

Pathogenic mechanisms shared between psoriasis and cardiovascular disease

Psoriasis is associated with an increased risk of cardiovascular disease, a hallmark of which is atherosclerosis. The objective of this study was to review the pertinent literature and highlight pathogenic mechanisms shared between psoriasis and atherosclerosis in an effort to advocate early therapeutic or preventive measures. We conducted a review of the current literature available from several biomedical search databases focusing on the developmental processes common between psoriasis and atherosclerosis. Our results revealed that the pathogenic mechanisms shared between the two diseases converged onto "inflammation" phenomenon. Within the lymph nodes, antigen-presenting cells activate naive T-cells to increase expression of LFA-1 following which activated T-cells migrate to blood vessel and adhere to endothelium. Extravasation occurs mediated by LFA-1 and ICAM-1 (or CD2 and LFA-3) and activated T-cells interact with dendritic cells (and macrophages and keratinocytes in psoriasis or smooth muscle cells in atherosclerosis). These cells further secrete chemokines and cytokines that contribute to the inflammatory environment, resulting in the formation of psoriatic plaque or atherosclerotic plaque. Additionally, some studies indicated clinical improvement in psoriasis condition with treatment of associated hyperlipidemia. In conclusion, therapeutic or preventive strategies that both reduce hyperlipidemia and suppress inflammation provide potentially useful approaches in the management of both diseases.

Biology of interleukin-22

Interleukin (IL)-22 is a member of the IL-10 family of cytokines and represents an important effector molecule of activated Th22, Th1, and Th17 cells, as well as Tc-cell subsets, gammadelta T cells, natural killer (NK), and NKT cells. IL-22 mediates its effects via a heterodimeric transmembrane receptor complex consisting of IL-22R1 and IL-10R2 and subsequent Janus kinase-signal transducers and activators of transcription (JAK-STAT) signaling pathways including Jak1, Tyk2, and STAT3. Whereas in some aspects, IL-22 acts synergistically with tumor necrosis factor-alpha, IL-1beta, or IL-17, most functions of IL-22 are unique. Importantly, IL-22 does not serve the communication between immune cells. It mainly acts on epithelial cells and hepatocytes, where it favors the antimicrobial defense, regeneration, and protection against damage and induces acute phase reactants and some chemokines. This chapter illuminates in detail the properties of IL-22 with respect to its gene, protein structure, cellular sources, receptors, target cells, biological effects, and, finally, its role in chronic inflammatory diseases, tumors, and infection.

The Th17 cytokine IL-22 induces IL-20 production in keratinocytes: a novel immunological cascade with potential relevance in psoriasis

Psoriasis is a common chronic skin disease. Recent studies demonstrated that IL-20 and IL-22, cytokines produced by keratinocytes and T cells, respectively, both inhibit keratinocyte terminal differentiation and induce psoriasis-like epidermis alterations. Here, we investigated the relationship between these mediators. Although IL-20 was not able to regulate IL-22 production, IL-22 induced IL-20 mRNA and protein in human keratinocytes. However, IL-22 had only a minimal effect, if any, on IL-19 and IL-26. Cutaneous IL-20 was also elevated in mice following IL-22 application. Accordingly, some of IL-22's effects on differentiation-regulating genes were partially mediated by an endogenous, secreted protein and attenuated by anti-IL-20 Ab. Like IL-22, IL-17A and TNF-alpha induced IL-20 in keratinocytes, whereas IFN-gamma and IL-20 itself did not. Furthermore, IL-17A and TNF-alpha individually strengthened the IL-22-induced IL-20 production. In lesional skin of psoriasis patients, highly elevated IL-20 levels strongly correlated with IL-22, and to a lesser extent, with IL-17A and TNF-alpha. As previously shown for IL-22, IL-20 blood levels correlated with the disease severity, although with a lower significance. This study demonstrates that a T-cell mediator induces a tissue cell mediator with similar effects to its own and therefore suggests the existence of a novel type of pathogenetic cascade.

A role for TGFbeta signaling in the pathogenesis of psoriasis

Deregulation of transforming growth factor-beta (TGFbeta) signaling has been reported in human psoriasis. Our recent study using a keratin 5 promoter (K5.TGFbeta1(wt)) showed that transgenic mice expressing wild-type TGFbeta1 in the epidermis developed severe skin inflammation. Additional experimental data further support a direct role for TGFbeta1 overexpression in skin inflammation. First, we temporally induced TGFbeta1 expression in keratinocytes in our gene-switch TGFbeta1(wt) transgenic mice and found inflammation severity correlated with TGFbeta1(wt) transgene expression. Second, deletion of T cells in K5.TGFbeta1(wt) mice significantly delayed skin inflammation and associated epidermal hyperplasia/hyperkeratosis. Third, therapeutic approaches effective for human psoriasis, that is, Etanercept and Rosiglitazone, are effective in alleviating the symptoms observed in K5.TGFbeta1(wt) mice. Future studies will analyze specific mechanisms and identify key factors in TGFbeta1-induced skin inflammation. Our mouse models will provide a useful tool for understanding the molecular mechanisms of inflammatory skin disorders in which TGFbeta1 is overexpressed.

Potential skin antiinflammatory effects of 4-methylthiobutylisothiocyanate (MTBI) isolated from rocket (Eruca sativa) seeds

Isothiocyanates (ITCs), which are organosulfur compounds present in cruciferous vegetables, have anticarcinogenic, antiinflammatory, and antiproliferative activities. These biological activities, and the knowledge that rocket seed (Eruca sativa) extract is used in skin disorders in traditional Middle Eastern medicine, led to the isolation and assessment of 4-methylthiobutylisothiocyanate (MTBI), the major ITC in rocket seeds, for its potential in the prevention of inflammatory skin diseases, such as psoriasis. MTBI was found to depress the growth of activated keratinocytes and to arrest the activated THP-1 monocytes in the G2 stage. Both MTBI and its oxidized derivative sulforaphane (SFN), which was found in the rocket seed at a low concentration, downregulated the expression of the proinflammatory genes, tumor necrosis factor (TNF)-alpha and interleukin (IL)-12/23 p40, as well as that of intercellular adhesion molecule-1, in activated THP-1 cells. These results demonstrate that MTBI may deter the inflammation process, as has been reported for SFN. Furthermore, pretreatment with MTBI hindered the induction of the inflammatory state in the THP-1 cells, as shown by the inhibition of cytokine mRNA expression of IL-1beta, IL-12/23 p40, and TNF-alpha. Overall, our results imply that MTBI may represent a new family of natural compounds possessing significant skin inflammation-preventive activities.

IL-24: a classic cytokine and/or a potential cure for cancer?

IL-24, a member of the IL-10 family of cytokines, is produced by monocytes and Th2 cells. Interestingly, immune cells do not appear to express specific IL-24 receptor chains (IL-20R1/IL-20R2 and IL-22R/IL-20R2), it is therefore unlikely that IL-24 has classical immune-modulating properties. Skin, on the other hand, seems to represent a major target tissue for IL-24 and related cytokines such as IL-19, -20, and -22. However, the initial interest in IL-24 did not arise from its physiological signalling properties through its cognate receptors but rather because of its tentative ability to selectively kill different cancer cells. In an attempt to further investigate the signalling events underlying the IL-24-induced cancer cell death, we found that melanoma cell lines did not react in the expected and previously described way. Using several different forms and delivery modes of IL-24, we were unable to detect any apoptosis-inducing properties of this cytokine in melanoma cells. In the present ‘Point of view’ we will briefly summarizse these findings and put them in context of published reports stating that IL-24 might be a long sought after treatment for several types of cancer.

Detection of psoriasin/S100A7 in the sera of patients with psoriasis

BACKGROUND

Psoriasis is a disease of dysregulated inflammation and epithelial hyperproliferation in the skin, involving both the innate and adaptive immune system. Psoriatic keratinocytes express high levels of psoriasin (S100A7), a small calcium-binding protein.

OBJECTIVES

To determine if patients with active psoriasis have elevated serum levels of psoriasin and psoriasin-specific autoantibodies.

METHODS

Blood was collected from 14 patients with psoriasis vulgaris at the start of narrowband ultraviolet (UV) B therapy and from 11 of these patients every 2 weeks during the course of the UVB treatment. Patient and control sera were tested for psoriasin antigen levels by sandwich enzyme-linked immunosorbent assay, and for psoriasin autoantibody titres using recombinant purified psoriasin and overlapping peptides.

RESULTS

We confirmed strong and specific expression of psoriasin in psoriatic epidermis by immunohistochemistry. Systemic psoriasin antigen levels tended to be lower in patients (mean 213 ng mL(-1)) than in controls (mean 331 ng mL(-1), P = 0.308) and decreased with increasing disease severity. Psoriasin-specific autoantibodies were detected in a subset of patients with psoriasis and healthy normal donors (mean 0.347 vs. 0.255 units, P = 0.246). The epitopes recognized by the autoantibodies were mapped to an external loop domain of the molecule but did not show corresponding T-cell immunogenicity.

CONCLUSIONS

Although psoriasin is overexpressed in psoriatic skin lesions, systemic levels of psoriasin tended to be lower with increasing disease severity, which may be due to the presence of psoriasin-specific autoantibodies. Neither psoriasin nor psoriasin-specific autoantibodies appear to be promising serum biomarkers for clinical psoriasis.

Th17 cells: a new therapeutic target in inflammatory dermatoses

Th17 cells, named for their secretion of interleukin-17 (IL-17), are a new class of T-cells involved in a wide range of cutaneous autoimmune and inflammatory conditions. An overactive Th17 cell response in the skin can produce damaging results. There appears to be a partial role for the Th17 axis in the pathogenesis of a range of dermatological diseases including allergic contact dermatitis, atopic dermatitis, psoriasis, and scleroderma. Immunologists have also discovered a unique association between Th17 cells and cutaneous T-cell lymphoma. The Th17 branch has been linked to a number of additional systemic inflammatory diseases with significant cutaneous pathology such as systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, and Behcet's disease. Newly developed treatment modalities for neutralizing the Th17 branch of the immune system are proving to be valuable additions to the current therapeutic armamentarium.