Psoriasis--as an autoimmune disease caused by molecular mimicry

The immunological understanding on germinal center B cells in psoriasis

The development of psoriasis is mainly driven by the dysregulation of T cells within the skin, marking a primary involvement of these cells in the pathogenesis. Although B cells are integral components of the immune system, their role in the initiation and progression of psoriasis is not as pivotal as that of T cells. The paradox of B cell suggests that, while it is crucial for adaptive immunity, B cells may contribute to the exacerbation of psoriasis. Numerous ideas proposed that there are potential relationships between psoriasis and B cells especially within germinal centers (GCs). Recent research projected that B cells might be triggered by autoantigens which then induced molecular mimicry to alter B cells activity within GC and generate autoantibodies and pro-inflammatory cytokines, form ectopic GC, and dysregulate the proliferation of keratinocytes. Hence, in this review, we gathered potential evidence indicating the participation of B cells in psoriasis within the context of GC, aiming to enhance our comprehension and advance treatment strategies for psoriasis thus inviting many new researchers to investigate this issue.

Etiopathogenesis of Psoriasis: Integration of Proposed Theories

Psoriasis is a chronic inflammatory disease characterized by squamous and erythematous plaques on the skin and the involvement of the immune system. Global prevalence for psoriasis has been reported around 1-3% with a higher incidence in adults and similar proportions between men and women. The risk factors associated with psoriasis are both extrinsic and intrinsic, out of which a polygenic predisposition is a highlight out of the latter. Psoriasis etiology is not yet fully described, but several hypothesis have been proposed: 1) the autoimmunity hypothesis is based on the over-expression of antimicrobial peptides such as LL-37, the proteins ADAMTSL5, K17, and hsp27, or lipids synthesized by the PLA2G4D enzyme, all of which may serve as autoantigens to promote the differentiation of autoreactive lymphocytes T and unleash a chronic inflammatory response; 2) dysbiosis of skin microbiota hypothesis in psoriasis has gained relevance due to the observations of a loss of diversity and the participation of pathogenic bacteria such as Streptococcus spp. or Staphylococcus spp. the fungi Malassezia spp. or Candida spp. and the virus HPV, HCV, or HIV in psoriatic plaques; 3) the oxidative stress hypothesis, the most recent one, describes that the cell injury and the release of proinflammatory mediators and antimicrobial peptides that leads to activate of the Th1/Th17 axis observed in psoriasis is caused by a higher release of reactive oxygen species and the imbalance between oxidant and antioxidant mechanisms. This review aims to describe the mechanisms involved in the three hypotheses on the etiopathogeneses of psoriasis.

The Use of Microbial Modifying Therapies to Prevent Psoriasis Exacerbation and Associated Cardiovascular Comorbidity

Psoriasis has emerged as a systemic disease characterized by skin and joint manifestations as well as systemic inflammation and cardiovascular comorbidities. Many progresses have been made in the comprehension of the immunological mechanisms involved in the exacerbation of psoriatic plaques, and initial studies have investigated the mechanisms that lead to extracutaneous disease manifestations, including endothelial disfunction and cardiovascular disease. In the past decade, the involvement of gut dysbiosis in the development of pathologies with inflammatory and autoimmune basis has clearly emerged. More recently, a major role for the skin microbiota in establishing the immunological tolerance in early life and as a source of antigens leading to cross-reactive responses towards self-antigens in adult life has also been evidenced. Gut microbiota can indeed be involved in shaping the immune and inflammatory response at systemic level and in fueling inflammation in the cutaneous and vascular compartments. Here, we summarized the microbiota-mediated mechanisms that, in the skin and gut, may promote and modulate local or systemic inflammation involved in psoriatic disease and endothelial dysfunction. We also analyze the emerging strategies for correcting dysbiosis or modulating skin and gut microbiota composition to integrate systemically existing pharmacological therapies for psoriatic disease. The possibility of merging systemic treatment and tailored microbial modifying therapies could increase the efficacy of the current treatments and potentially lower the effect on patient's life quality.

Immune-mediated inflammatory diseases: Common and different pathogenic and clinical features

The term "immune-mediated inflammatory diseases (IMIDs)" refers to several inflammatory pathologies of multifactorial etiology and involving either simultaneously or sequentially more organs. IMIDs share some common pathogenic mechanisms, which account for some similarities in the clinical course and the impact that these diseases may have on other organs and systems of the body. However, there are some differences in the IMID-associated pathological process, including the synthesis and function of multiple inflammatory cytokines, which are supposed to perpetuate the tissue-damaging inflammation. This justifies the different indications and responsiveness to corticosteroids, immunosuppressors, small molecules, and biologics. Many individuals with IMIDs are, however, intolerant, or unresponsive to the current drugs, thus suggesting the necessity of novel therapeutic approaches, such as the combination of compounds that either inhibit more immuno-inflammatory networks selectively or simultaneously suppress inflammatory signals and activate counter-regulatory pathways. In this article, we highlight the most relevant features of IMIDs and discuss how clinicians can combat the detrimental immune response in such disorders.

Friend or Foe - Tc17 cell generation and current evidence for their importance in human disease

The term Tc17 cells refers to interleukin 17 (IL-17)-producing CD8+ T cells. While IL-17 is an important mediator of mucosal defense, it is also centrally involved in driving the inflammatory response in immune-mediated diseases, such as psoriasis, multiple sclerosis, and inflammatory bowel disease. In this review, we aim to gather the current knowledge on the phenotypic and transcriptional profile, the in vitro and in vivo generation of Tc17 cells, and the evidence pointing towards a relevant role of Tc17 cells in human diseases such as infectious diseases, cancer, and immune-mediated diseases.

Complimentary electrostatics dominate T Cell Receptor binding to a psoriasis-associated-peptide-antigen presented by Human Leukocyte Antigen (HLA) C*06:02

Psoriasis is a chronic skin disease characterised by hyperproliferative epidermal lesions infiltrated by autoreactive T cells. Individuals expressing the Human Leukocyte antigen (HLA) C*06:02 allele are at highest risk for developing psoriasis. An autoreactive T cell clone (termed Vα3S1/Vβ13S1) isolated from psoriatic plaques is selective for HLA-C*06:02-presenting a peptide derived from the melanocyte-specific auto-antigen ADAMTSL5 (VRSRRCLRL). Here we determine the crystal structure of this psoriatic TCR-HLA-C*06:02- ADAMTSL5 complex with a stabilised peptide. Docking of the TCR involves an extensive complementary charge network formed between negatively charged TCR residues interleaving with exposed arginine residues from the self-peptide and the HLA-C*06:02 α1 helix. We probed these interactions through mutagenesis and activation assays. The charged interface spans the polymorphic region of the C1/C2 HLA group. Notably the peptide binding groove of HLA C*06:02 appears exquisitely suited for presenting highly charged Arg-rich epitopes recognised by this acidic psoriatic TCR. Overall, we provide a structural basis for understanding engagement of melanocyte antigen-presenting cells by a TCR implicated in psoriasis, while simultaneously expanding our knowledge of how TCRs engage HLA-C.

Group A Streptococcus induces CD1a-autoreactive T cells and promotes psoriatic inflammation

Group A Streptococcus (GAS) infection is associated with multiple clinical sequelae, including different subtypes of psoriasis. Such post-streptococcal disorders have been long known but are largely unexplained. CD1a is expressed at constitutively high levels by Langerhans cells and presents lipid antigens to T cells, but the potential relevance to GAS infection has not been studied. Here, we investigated whether GAS-responsive CD1a-restricted T cells contribute to the pathogenesis of psoriasis. Healthy individuals had high frequencies of circulating and cutaneous GAS-responsive CD4+ and CD8+ T cells with rapid effector functions, including the production of interleukin-22 (IL-22). Human skin and blood single-cell CITE-seq analyses of IL-22-producing T cells showed a type 17 signature with proliferative potential, whereas IFN-γ-producing T cells displayed cytotoxic T lymphocyte characteristics. Furthermore, individuals with psoriasis had significantly higher frequencies of circulating GAS-reactive T cells, enriched for markers of activation, cytolytic potential, and tissue association. In addition to responding to GAS, subsets of expanded GAS-reactive T cell clones/lines were found to be autoreactive, which included the recognition of the self-lipid antigen lysophosphatidylcholine. CD8+ T cell clones/lines produced cytolytic mediators and lysed infected CD1a-expressing cells. Furthermore, we established cutaneous models of GAS infection in a humanized CD1a transgenic mouse model and identified enhanced and prolonged local and systemic inflammation, with resolution through a psoriasis-like phenotype. Together, these findings link GAS infection to the CD1a pathway and show that GAS infection promotes the proliferation and activation of CD1a-autoreactive T cells, with relevance to post-streptococcal disease, including the pathogenesis and treatment of psoriasis.

DNA sensing via the cGAS/STING pathway activates the immunoproteasome and adaptive T-cell immunity

The immunoproteasome is a specialized type of proteasome involved in MHC class I antigen presentation, antiviral adaptive immunity, autoimmunity, and is also part of a broader response to stress. Whether the immunoproteasome is regulated by DNA stress, however, is not known. We here demonstrate that mitochondrial DNA stress upregulates the immunoproteasome and MHC class I antigen presentation pathway via cGAS/STING/type I interferon signaling resulting in cell autonomous activation of CD8⁺ T cells. The cGAS/STING-induced adaptive immune response is also observed in response to genomic DNA and is conserved in epithelial and mesenchymal cells of mice and men. In patients with idiopathic pulmonary fibrosis, chronic activation of the cGAS/STING-induced adaptive immune response in aberrant lung epithelial cells concurs with CD8⁺ T-cell activation in diseased lungs. Genetic depletion of the immunoproteasome and specific immunoproteasome inhibitors counteract DNA stress induced cytotoxic CD8⁺ T-cell activation. Our data thus unravel cytoplasmic DNA sensing via the cGAS/STING pathway as an activator of the immunoproteasome and CD8⁺ T cells. This represents a novel potential pathomechanism for pulmonary fibrosis that opens new therapeutic perspectives.

Intranasal streptococcal infection exacerbates psoriasis-like dermatitis via the induction of skin tissue-resident memory T cells

Recurrent streptococcal tonsillitis exacerbates psoriasis. Studies have indicated that T cells responding to streptococcal antigens in the skin are involved in the pathogenesis of the disease. However, a direct link between streptococcal tonsillitis and psoriasis has not been evidenced. In the present study, the impact of intranasal (i.n.) streptococcal infection on psoriasis was investigated using the imiquimod (IMQ) psoriasis mouse model. The results showed that repeated i.n. infection with group A Streptococcus (GAS) induced a robust and persistent Th17 response in the nasal-associated lymphoid tissue (NALT) and exacerbated IMQ-mediated psoriatic skin lesions. ELISpot and flow cytometry analyses revealed that GAS-reactive tissue-resident memory T cells (T_RM) were present in the skin of GAS-infected mice and produced IL-17/IL-23 axis cytokines in response to IMQ, compared to mice uninfected with GAS. In addition, i.n. infection with Streptococcus pneumoniae (Sp), a pathogen not associated with the development of psoriasis, also induced a persistent Th17 response in NALT but did not exacerbate IMQ-induced psoriatic inflammation nor elicited Sp-specific T cells in the skin. The results provide in vivo evidence that GAS-associated psoriasis is dependent on the skin GAS-specific T_RM cells induced by GAS nasopharyngeal infection and can be later activated by environmental triggers, leading to psoriatic inflammation. Reducing the reservoir of Th17 cells, which are source of skin T_RM cells, may constitute a promising treatment for psoriasis.

New aspects of the pathogenesis of psoriasis

Psoriasis is a chronic multi-factorial immune-mediated inflammatory disease of skin and joints. The variety of clinical forms of dermatosis is consistent with various pathogenetic features of the disease progress which have been significantly supplemented and reviewed recently. Knowledge of these mechanisms will improve and personalize the prescribed therapy. This study places the emphasis on modern ideas about the formation of T cell memory, the role of melanocytes and innate lymphoid cells. Development mechanisms of guttate and paradoxical psoriasis with important distinguishing characteristics are described separately. Today, knowledge of the molecular basis of the disease progression has led to the creation and introduction of a number of highly effective targeted drugs into clinical practice. Further developments related to the inhibition of resident memory cells, innate lymphoid cells, as well as the study of guttate psoriasis perpetuation and the occurrence of paradoxical psoriasis will significantly increase the effectiveness of the therapy.

Latest on biomaterial-based therapies for topical treatment of psoriasis

Psoriasis is an autoimmune inflammatory disease which is fundamentally different from dermatitis. Its treatments include topical medications and systemic drugs depending on different stages of the disease. However, these commonly used therapies are falling far short of clinical needs due to various drawbacks. More precise therapeutic strategies with minimized side effects and improved compliance are highly demanded. Recently, the rapid development of biomaterial-based therapies has made it possible and promising to attain topical psoriasis treatment. In this review, we briefly describe the significance and challenges of the topical treatment of psoriasis and emphatically overview the latest progress in novel biomaterial-based topical therapies for psoriasis including microneedles, nanoparticles, nanofibers, and hydrogels. Current clinical trials related to each biomaterial are also summarized and discussed.

Roles of Infection in Psoriasis

Psoriasis is a chronic, immune-mediated disorder with cutaneous and systemic manifestations. Genetic predisposition, environmental factors, and immune dysfunction all contribute to the pathogenesis of psoriasis with host-microbe interaction governing the progression of this disease. Emerging evidence has indicated that infection is an environmental trigger for psoriasis and plays multiple roles in its maintenance as evidenced by the frequent association between guttate psoriasis onset and acute streptococcal infection. Different infectious factors act on immune cells to produce inflammatory cytokines that can induce or aggravate psoriasis. In addition to bacterial infections, viral and fungal infections have also been shown to be strongly associated with the onset or exacerbation of psoriasis. Intervention of skin microbiota to treat psoriasis has become a hot research topic. In this review, we summarize the effects of different infectious factors (bacteria, viruses, and fungi) on psoriasis, thereby providing insights into the manipulation of pathogens to allow for the identification of improved therapeutic options for the treatment of this condition.

Topical Formulation of Noscapine, a Benzylisoquinoline Alkaloid, Ameliorates Imiquimod-Induced Psoriasis-Like Skin Lesions

Psoriasis is considered an autoimmune inflammatory disease. The disease is spread and diagnosed by the infiltration of inflammatory mediators and cells into the epidermis. Recent theoretical developments have focused on the effectiveness of noscapine (NOS) as a potential alkaloid for being used as a valuable treatment for different diseases. In the present study, psoriasis-like dermatitis was induced on the right ear pinna surface of male Balb/c mice by topical application of imiquimod (IMQ) for ten consecutive days, which was treated with noscapine (0.3, 1, 3, and 10% w/v) or clobetasol (0.05% w/v) as a positive control. The levels of ear length, thickness, severity of skin inflammation, psoriatic itch, psoriasis area severity index (PASI) score, and body weight were measured daily. On the 10^th day of study, each ear was investigated for inflammation, fibrosis, proliferation, and apoptosis using histopathological (H&E and Masson's trichrome staining) and immunohistochemistry (Ki67 and p53 staining) assays. Furthermore, the levels of inflammatory biomarkers were characterized by an enzyme-linked immunosorbent assay (ELISA). The results confirmed IMQ-induced psoriasis for five consecutive days. In contrast, noscapine significantly reduced the ear length, thickness, severity of skin inflammation, psoriatic itch and body weight, tumor necrosis factor-α (TNF-α), transforming growth factor-β (TGF-β), interferon-gamma (IFN-γ), interleukin 6 (IL-6), IL-17, and IL-23p19 in a concentration-dependent manner (P < 0.001–0.05 for all cases). Overall, topical noscapine significantly ameliorated both the macroscopical and microscopical features of psoriasis. However, further clinical investigations are required to translate the effects to clinics.

The impact of external factors on psoriasis

Psoriasis is one of the most common chronic inflammatory skin diseases, constituting a significant health and socioeconomic problem. Despite numerous therapeutic options, the results of treatment very often remain insufficient. It is extremely important to remember that many external factors impact the effectiveness of therapy. This article discusses the importance of emollients in therapy and the influence of infectious agents and injuries on the course of psoriasis. Understanding the above-mentioned factors in the treatment of psoriasis is critical to achieve satisfactory therapeutic effects.

The Role of Helper T Cells in Psoriasis

Psoriasis is a complex, chronic relapsing and inflammatory skin disorder with a prevalence of approximately 2% in the general population worldwide. Psoriasis can be triggered by infections, physical injury and certain drugs. The most common type of psoriasis is psoriasis vulgaris, which primarily features dry, well-demarcated, raised red lesions with adherent silvery scales on the skin and joints. Over the past few decades, scientific research has helped us reveal that innate and adaptive immune cells contribute to the chronic inflammatory pathological process of psoriasis. In particular, dysfunctional helper T cells (Th1, Th17, Th22, and Treg cells) are indispensable factors in psoriasis development. When stimulated by certain triggers, antigen-presenting cells (APCs) can release pro-inflammatory factors (IL-23, IFN-α and IL-12), which further activate naive T cells and polarize them into distinct helper T cell subsets that produce numerous cytokines, such as TNF, IFN-γ, IL-17 and IL-22, which act on keratinocytes to amplify psoriatic inflammation. In this review, we describe the function of helper T cells in psoriasis and summarize currently targeted anti-psoriatic therapies.

Interleukin-1 Links Autoimmune and Autoinflammatory Pathophysiology in Mixed-Pattern Psoriasis

Autoinflammatory and autoimmune diseases are characterized by an oversensitive immune system with loss of the physiological endogenous regulation, involving multifactorial self-reactive pathological mechanisms of mono- or polygenic nature. Failure in regulatory mechanisms triggers a complex network of dynamic relationships between innate and adaptive immunity, leading to coexistent autoinflammatory and autoimmune processes. Sustained exposure to a trigger or a genetic alteration at the level of the receptors of the natural immune system may lead to abnormal activation of the innate immune system, adaptive system activation, loss of self-tolerance, and systemic inflammation. The IL-1 family members critically activate and regulate innate and adaptive immune responses' diversity and plasticity in autoimmune and/or autoinflammatory conditions. The IL-23/IL-17 axis is key in the communication between innate immunity (IL-23-producing myeloid cells) and adaptive immunity (Th17- and IL-17-expressing CD8+ T cells). In psoriasis, these cytokines are decisive to the different clinical presentations, whether as plaque psoriasis (psoriasis vulgaris), generalized pustular psoriasis (pustular psoriasis), or mixed forms. These forms reflect a gradient between autoimmune pathophysiology with predominant adaptive immune response and autoinflammatory pathophysiology with predominant innate immune response.

The power and potential of BIOMAP to elucidate host-microbiome interplay in skin inflammatory diseases

The two most common chronic inflammatory skin diseases are atopic dermatitis (AD) and psoriasis. The underpinnings of the remarkable degree of clinical heterogeneity of AD and psoriasis are poorly understood and, as a consequence, disease onset and progression are unpredictable and the optimal type and time-point for intervention are as yet unknown. The BIOMAP project is the first IMI (Innovative Medicines Initiative) project dedicated to investigating the causes and mechanisms of AD and psoriasis and to identify potential biomarkers responsible for the variation in disease outcome. The consortium includes 7 large pharmaceutical companies and 25 non-industry partners including academia. Since there is mounting evidence supporting an important role for microbial exposures and our microbiota as factors mediating immune polarization and AD and psoriasis pathogenesis, an entire work package is dedicated to the investigation of skin and gut microbiome linked to AD or psoriasis. The large collaborative BIOMAP project will enable the integration of patient cohorts, data and knowledge in unprecedented proportions. The project has a unique opportunity with a potential to bridge and fill the gaps between current problems and solutions. This review highlights the power and potential of BIOMAP project in the investigation of microbe-host interplay in AD and psoriasis.

Antigen Processing, Presentation, and Tolerance: Role in Autoimmune Skin Diseases

Autoreactive T cells pose a constant risk for the emergence of autoimmune skin diseases in genetically predisposed individuals carrying certain HLA risk alleles. Immune tolerance mechanisms are opposed by broad HLA-presented self-immunopeptidomes, a predefined repertoire of polyspecific TCRs, the continuous generation of new antibody specificities by somatic recombination of Ig genes in B cells, and heightened proinflammatory reactivity. Increased autoantigen presentation by HLA molecules, cross-activation of pathogen-induced T cells against autologous structures, altered metabolism of self-proteins, and excessive production of proinflammatory signals may all contribute to the breakdown of immune tolerance and the development of autoimmune skin diseases.

SARS-CoV-2 and guttate psoriasis: A case report and review of literature

Guttate psoriasis is a rare dermatological presentation of SARS-CoV-2 infection and is seen mainly in patients with an underlying disease psoriasis.

[Dysbalance between the immune system and skin microbiome in chronic inflammatory dermatoses]

BACKGROUND

The skin is an organ frequently affected by chronic diseases. Inflammatory, immune-mediated dermatoses such as atopic dermatitis and psoriasis show a high prevalence as well as a significant impact on the quality of life of those affected. In a large proportion of cases, atopic dermatitis is associated with a marked change in microbial colonization of both clinically healthy and affected skin. In psoriasis, changes to this effect have been described, but clinical relevance remains elusive.

AIM

In recent years, increasing knowledge has been gained in microbiome research with resulting clinical relevance. The present article deals with the disturbed balance of the immune system and the skin microbiome in chronic inflammatory dermatoses on the basis of atopic dermatitis and psoriasis vulgaris.

MATERIALS AND METHODS

A literature search was performed in PubMed and Medline databases (entries until 09 April 2021).

RESULTS

Staphylococcus aureus is known to play a central pathophysiological role in atopic dermatitis. This is revisited in light of new insights regarding biodiversity and immunoregulatory processes. In psoriasis, a more heterogeneous body of data emerges regarding the microbiome and its contribution to disease development.

DISCUSSION

While topical applications to directly influence the microbiome are already being tested in atopic dermatitis, further knowledge regarding the pathophysiological significance of the microbiota is still needed in psoriasis.

Psoriasis: Embarking a dynamic shift in the skin microbiota

Recent interest has arisen regarding the role of microbiome and its composition in the pathogenesis of psoriasis. Numerous studies have shown that there are alterations in skin flora arrangement between normal individuals and psoriatic patients. Psoriasis exacerbation could be interconnected with epidermal or mucosal colonization with streptococci, Malassezia, Staphylococcus aureus, or Candida albicans. The role of cutaneous and gut microbiome in psoriasis pathogenesis has recently been studied in both human and animal models. In this review, we try to evaluate various pathogenic mechanisms linking the microbiota and psoriasis. The literature research included peer-reviewed articles which included clinical trials, original reports, and scientific reviews. MEDLINE and PubMed databases were searched from January 1990 to March 2021, including the reference lists of articles meeting our criteria.

Infection-provoked psoriasis: Induced or aggravated (Review)

Psoriasis is a common chronic, immune-mediated, inflammatory skin disorder, with a reported prevalence of 0.0-2.1% among children and 0.91-8.50% among adults, worldwide. Psoriasis is induced by several environmental factors, including infection, alcohol consumption, drugs, trauma, acute withdrawal of systemic or potent topical corticosteroids, body mass index and endocrine disorders. Increasing evidence suggest that a variety of microorganisms play key roles in the induction and exacerbation of psoriasis. Pathogens, such as streptococci and staphylococci are considered causal factors, presumably via superantigen activation of skin-seeking T cells. In addition, fungal pathogens, such as Candida and Malassezia, and viral agents, such as human immunodeficiency virus, hepatitis C virus infection and human papillomavirus, are also closely associated with psoriasis. Recently, several types of pathogens, such as Helicobacter pylori infection, Zika virus and scabies, have been reported to potentially trigger psoriasis. The present review discusses the underlying molecular mechanisms by which these infections influence psoriasis to provide a better understanding of the pathogenesis of psoriasis.

Functional study of TNF-α promoter polymorphisms in psoriasis

BACKGROUND

TNF-α is an important mediator in the pathogenesis of psoriasis and polymorphisms influence its transcription and could be implicated in psoriasis risk and modify certain aspects of disease, such as age at onset of psoriasis vulgaris and disease severity. Six TNF-α single nucleotide polymorphisms (SNPs) in promoter region has been identified and studied but with discordant results. The aim of this study was to evaluate whether the polymorphisms in TNF-α (-238 (rs361525), -308 (rs1800629), -857 (rs1799724), -1031 (rs1799964)) are associated with gravity, prurity, early onset or response to drug therapy in psoriasis in Caucasian Italian patients.

METHODS

58 psoriasis patients from Turin PSOCARE, 23 with psoriasis vulgaris and 35 with psoriatic arthritis were studied. Ready to used master mix for allelic discrimination of rs1800629, rs361525 and rs1799964 respectively.

RESULTS

Our data showed a significant association between the -857(G) variant and both VAS-itch (p=0,03) and VAS-pain index (p=0,006), OR=0,2 (0,04-0,98) and OR=0,12 (0,02-0,59). No significant association between the genotypes or alleles of TNF-α SNPs as been observed with other clinic-pathologic parameters or etanercept response.

CONCLUSIONS

Our data suggest that -857 CC genotype could be involved in pain and itch severity in psoriasis patients.

Immune responses and therapeutic options in psoriasis

Psoriasis is a chronic inflammatory disease of the skin that affects about 2-3% of the population and greatly impairs the quality of life of affected individuals. Psoriatic skin is characterized by excessive proliferation and aberrant differentiation of keratinocytes, as well as redness caused by increased dilation of the dermal blood vessels and infiltration of immune cells. Although the pathogenesis of psoriasis has not yet been completely elucidated, it is generally believed to arise from a complex interplay between hyperproliferating keratinocytes and infiltrating, activated immune cells. So far, the exact triggers that elicit this disease are still enigmatic, yet, it is clear that genetic predisposition significantly contributes to the development of psoriasis. In this review, we summarize current knowledge of important cellular and molecular mechanisms driving the initiation and amplification stages of psoriasis development, with a particular focus on cytokines and emerging evidence illustrating keratinocyte-intrinsic defects as key drivers of inflammation. We also discuss mouse models that have contributed to a better understanding of psoriasis pathogenesis and the preclinical development of novel therapeutics, including monoclonal antibodies against specific cytokines or cytokine receptors that have revolutionized the treatment of psoriasis. Future perspectives that may have the potential to push basic research and open up new avenues for therapeutic intervention are provided.

Tonsillectomy and the subsequent risk of psoriasis: A nationwide population-based cohort study

BACKGROUND

Tonsillectomy has been suggested as an intervention to resolve psoriasis.

OBJECTIVE

This study aimed to investigate the subsequent risk of psoriasis in patients who received tonsillectomy.

METHODS

We used data from the Taiwan National Health Insurance Research Database. The tonsillectomy group (case group) and the tonsillectomy-free group (comparison group) were matched at a ratio of 1:4 by demographic data, comorbidities, medical confounders, and the index date. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

We identified 2021 patients as the case group and matched 8084 individuals as the comparison group. The adjusted HR (aHR) of psoriasis was 0.43 (95% CI, 0.22-0.87; P < .05). The study population is composed of a mainly male (65%) and young population (mostly younger than 50 years). Notably, patients with rheumatoid arthritis increased the risk of psoriasis (aHR, 3.97; 95% CI, 1.17-13.48; P < .05). In our stratification analysis, the risk of psoriasis decreased in almost all subgroups.

LIMITATION

Our database did not include information on genome and the subtypes of psoriasis.

CONCLUSION

Our study showed a decreased risk of psoriasis in the tonsillectomy group after adjustment for baseline characteristics, comorbidities, and medical confounders compared with the reference group.

Could basement membrane alterations, resembling micro-wounds at the dermo-epidermal junction in psoriatic non-lesional skin, make the skin susceptible to lesion formation?

Current data suggest that tissue microenvironment control immune functions. Therefore, understanding the tissue environment in which immune activation occurs will enhance our capability to interfere with abnormal immune pathology. Here, we argue that studying the constitutively abnormal functions of clinically uninvolved psoriatic skin in patients with plaque type psoriasis is very important to better understand psoriasis pathobiology, because non-lesional skin provides the tissue environment in which the psoriatic lesion develops. A key question in psoriasis is what initiates the abnormal, uncontrolled immune activation in the first place and the answer may lie in the skin. In light of this concept, we summarize abnormalities at the dermal-epidermal junction region which shows a special "non-healing-like" micro-wound phenotype in the psoriatic non-lesional skin that may act as a crucial susceptibility factor in the development of the disease.

Microbiome analysis of contact lens care solutions and tear fluids of contact lens wearers: Possible involvement of streptococcal antigens in allergic symptoms related to contact lens wear

The present study elucidated the pathogenesis of allergic symptoms (AS) related to contact lens (CL) wear by assaying CL care solutions in lens storage cases and tears from subjects with AS using molecular biology techniques. A total of 15 CL storage cases were collected from subjects with AS (n=9) and healthy, asymptomatic control CL wearers (n=6). Bacterial populations in CL care solutions and tears were assayed by culture and 16S rDNA sequencing. Histamine levels in tears were measured by high-performance liquid chromatography. Western blot analysis was performed to identify the bacteria recognized by tear IgE from subjects with AS. No significant differences were found in the culture results between the subjects with AS and asymptomatic subjects. Histamine was detected in 2 subjects with AS. Meta-16S rDNA sequencing identified a cluster of 4 subjects with AS that were distinguished from others by principal coordinate analysis. Detailed population analysis revealed that the abundance of Gram-positive bacteria in the microbiomes of CL care solutions used by the subjects with AS were higher than those of asymptomatic subjects (42.24±9.47 vs. 16.85±22.76% abundance). Among these, Streptococcus was the dominant genus (12.1-18.3% abundance). Tear microbiome analysis revealed that the abundance of Streptococcus in the subjects with AS was significantly higher than that in other subjects (19.02±5.50 vs. 3.08±3.35%, P<0.01). Western blot analysis demonstrated that the tear IgE in all subjects with AS reacted with Streptococcus (100%), but not with Staphylococcus. On the whole, these results provide novel insight into the pathogenesis of AS and identify Streptococcus as an important factor in AS associated with CL wear.

Cellular scars and local crosstalk in relapsing psoriasis: an example of a skin sticking disease

Psoriasis is an inflammatory disease that arises in genetically predisposed individuals. Chronic skin lesions that contain activated immune cells can persist for years. Systemic inhibition of TNF, IL‐17 and IL‐23 cytokines has revolutionized psoriasis care during the recent decades. Unfortunately, local relapse of disease is common at previously inflamed sites after cessation of treatment. This highlights that fundamental pathologic alterations of the affected tissues are not completely resolved during clinical remission. Here, we present arguments for a local disease memory located in both dermis and epidermis in psoriasis skin. We decipher different cellular components and intercellular crosstalk that sustain local disease memory and amplify disease relapse in human psoriasis. Decrypting the mechanisms underlying the establishment and persistence of pathogenic memory cells in resolved psoriasis may provide new therapeutic perspectives aimed at long‐term remission of psoriasis.

Association of Psoriasis with Autoimmune Disorders: Results of a Pilot Study

BACKGROUND

Association of psoriasis with other autoimmune diseases remains an ongoing research subject.

OBJECTIVES

To investigate the association of psoriasis with other autoimmune disorders.

MATERIALS AND METHODS

We studied 80 (M: F 57:23) psoriasis patients aged 13-75 years for concurrent autoimmune disorders. After clinical examination, hemogram, fasting blood sugar, HbA1c, thyroid function tests, anti-TPO antibody, rheumatoid factor, anti-tTG antibody, anti-CCP antibody, ANA, anti-dsDNA antibody, anti-Ro antibody, and fecal calprotectin were estimated.

RESULTS

Mild-to-moderate and severe psoriasis was present in 86.3% and 13.8% patients, respectively. Psoriatic arthritis was present in 3.8% patients, all of whom also had severe psoriasis. Only 37 (46.3%) patients had clinical and/or sero-abnormality suggestive of autoimmune disorders; vitiligo in 3.8%, type-1 diabetes mellitus (DM) in 1.3%, and type-2 DM in 6.3% patients. Sero-positivity reflecting subclinical autoimmunity was noted for anti-CCP antibodies (in 2.5%), rheumatoid factor (in 2.5%), hypo- or hyper-thyroidism (in 8.8%), anti-TPO antibodies (in 5.0%), anti-tTG antibody (in 1.3%), ANA (in 5.0%), anti-dsDNA antibody (in 2.5%), and anti-Ro antibody in 11.3% patients. Elevated fecal calprotectin levels suggestive of inflammatory bowel disease (IBD) occurred in 11.2% of 27 patients. Multiple abnormalities happened in 2.5% patients.

CONCLUSION

Apparently psoriasis patients seem to have a predilection for other autoimmune disorders particularly for vitiligo, diabetes mellitus, autoimmune thyroiditis, rheumatoid arthritis, and IBD. However, association between psoriasis and other autoimmune disorders at best remains tenuous for want of strong evidence. Nevertheless, screening for them will improve overall management of these patients. Cross-sectional study design and small number of study subjects remain important limitations.

Dialog between skin and its microbiota: Emergence of "Cutaneous Bacterial Endocrinology"

Microbial endocrinology is studying the response of microorganisms to hormones and neurohormones and the microbiota production of hormones-like molecules. Until now, it was mainly applied to the gut and revealed that the intestinal microbiota should be considered as a real organ in constant and bilateral interactions with the whole human body. The skin harbours the second most abundant microbiome and contains an abundance of nerve terminals and capillaries, which in addition to keratinocytes, fibroblasts, melanocytes, dendritic cells and endothelial cells, release a huge diversity of hormones and neurohormones. In the present review, we will examine recent experimental data showing that, in skin, molecules such as substance P, calcitonin gene-related peptide, natriuretic peptides and catecholamines can directly affect the physiology and virulence of common skin-associated bacteria. Conversely, bacteria are able to synthesize and release compounds including histamine, glutamate and γ-aminobutyric acid or peptides showing partial homology with neurohormones such as α-melanocyte-stimulating hormone (αMSH). The more surprising is that some viruses can also encode neurohormones mimicking proteins. Taken together, these elements demonstrate that there is also a cutaneous microbial endocrinology and this emerging concept will certainly have important consequences in dermatology.

The importance of intracellular bacterial biofilm in infectious diseases

Various bacterial species, previously known as extracellular pathogens, can reside inside different host cells by adapting to intracellular modes by forming microbial aggregates with similar characteristics to bacterial biofilms. Additionally, bacterial invasion of human cells leads to failure in antibiotic therapy, as most conventional anti-bacterial agents cannot reach intracellular biofilm in normal concentrations. Various studies have shown that bacteria such as uropathogenic Escherichia coli, Pseudomonas aeruginosa, Borrelia burgdorferi,Moraxella catarrhalis, non-typeable Haemophilus influenzae, Streptococcus pneumonia, and group A Streptococci produce biofilm-like structures within the host cells. For the first time in this review, we will describe and discuss the new information about intracellular bacterial biofilm formation and its importance in bacterial infectious diseases.

Targeting the cutaneous lymphocyte antigen (CLA) in inflammatory and neoplastic skin conditions

Introduction: The cutaneous lymphocyte antigen interacts with E-selectin on endothelial cells and is expressed on 15% of circulating T-cells. Skin-homing T-cells express the cutaneous lymphocyte antigen and play a role in local cutaneous immunity in inflammatory reactions and neoplastic conditions.Areas covered: Lymphocyte extravasation is the essential para-physiological mechanism enabling immune surveillance of tissues for tumors as well as effector cell recruitment to inflammatory sites.The authors focused on skin inflammatory disorders, on cutaneous lymphoproliferative disease, and on other skin malignancies.Expert opinion: Interfering with leukocyte extravasation has been regarded as an attractive strategy in skin disorders, in the past for inflammatory conditions and more recently for cutaneous T-cell lymphomas. Therapeutic blocking of skin-homing interactions has been attempted in psoriasis and atopic dermatitis and has been achieved in the treatment of cutaneous T-cell lymphomas. Cutaneous lymphocyte antigen is a potential molecular target for both systemic and skin-directed therapy for cutaneous T-cell lymphomas.

Specific IgA and CLA+ T-Cell IL-17 Response to Streptococcus pyogenes in Psoriasis

Streptococcus pyogenes tonsillar infection is well known to trigger and exacerbate psoriasis lesions in both guttate and plaque forms of the disease. Although mucosal and cutaneous tissues are closely involved in psoriasis pathology, the interaction between their specific immune responses has not been deeply explored. This work aims to address and characterize the presence of humoral responses against S. pyogenes in patients with psoriasis and its putative association with cytokine responses detected in vitro in our psoriasis ex vivo model, based on the coculture of cutaneous lymphocyte-associated antigen^+/- T cells with autologous epidermal cells. Patients with psoriasis presented increased IgA response to S. pyogenes when compared with control subjects. In patients with plaque psoriasis, despite being negative for anti-streptolysin O antibody titer, IgA plasma levels against S. pyogenes correlated with cutaneous lymphocyte-associated antigen⁺ T-cell-dependent IL-17F response in vitro. No association is observed for IgG levels in plaque psoriasis. Similar association is observed for IgA anti-S. pyogenes extract and IL-17A in patients with guttate psoriasis. We propose S. pyogenes-specific IgA as a potential new perspective for better understanding the role of S. pyogenes in psoriasis development.

Autoimmunity to heterogeneous nuclear ribonucleoprotein A1 in psoriatic patients and correlation with disease severity

BACKGROUND AND OBJECTIVES

The heterogeneous nuclear ribonucleoprotein A1 (hnRNP-A1) has been postulated as an autoantigen of psoriasis, but correlation between serum levels of anti-hnRNP-A1 autoantibodies and the severity of disease has not been investigated. We aimed to assess the frequency of anti-hnRNP-A1 autoimmunity in patients with moderate to severe psoriasis and in healthy controls, and to determine the correlation between serum levels of anti-hnRNP-A1 autoantibodies and disease severity.

PATIENTS AND METHODS

We performed a case-control study on 40 adult psoriatic patients with a PASI (Psoriasis Area and Severity Index) of > 10 and 40 healthy controls matched for age and gender. Immunoblotting was used to assess serum levels of anti-hnRNP-A1 autoantibodies.

RESULTS

Anti-hnRNP-A1 autoantibodies were found in 9/40 psoriatic patients (22.5 %) but in no healthy controls. The PASI was significantly higher in anti-hnRNP-A1-positive patients than in anti-hnRNP-A1-negative patients (40.33 ± 3.24 vs 26.06 ± 9.28, p = 0.0001). In patients positive for anti-hnRNP-A1, serum levels of such autoanti-bodies were correlated with the PASI (R = 0.89, p = 0.001).

CONCLUSIONS

Consistent with reports in the literature, our results suggest a role of anti-hnRNP-A1 autoimmunity in psoriasis, although probably not as the primary cause or initial/fundamental event. Unlike previously published reports, our results also suggest that anti-hnRNP-A1 autoimmunity is particularly frequent among psoriatic patients with more severe disease. Further studies are necessary with a larger number of patients.

Functional significance of MAIT cells in psoriatic arthritis

BACKGROUND

Mucosal-associated invariant T (MAIT) cells are gaining more relevance for autoimmune diseases because of its (i) innate and adaptive immune response (ii) tissue homing properties (iii) production of IL-17A. These cells are predominantly CD8⁺ cells, because of its strong association with MHC-I. Tc17 CD8+/MAIT cells likely to have a critical role in psoriatic arthritis (PsA). Herein, we have explored pathological significance of MAIT cell in PsA.

METHODS

Peripheral blood mononuclear cells (PBMC) and synovial fluid mononuclear cells (SFMC) were collected from age/sex matched (n = 10 for each) PsA, rheumatoid arthritis (RA) and osteoarthritis patients (OA). Hi-D FACS studies were performed: (i) activated memory cells (CD3⁺CD45RO⁺) T cells were identified (ii) gating strategies were made to identity the MAIT (CD3⁺Vα7.2TCR⁺CD161^hi) cells, its phenotype pattern; and functional significance in respect to IL-17A production and responsiveness to human rIL-23. Anti CD3/CD28 ab cocktail was used to activate cells along with rIL-23 to culture and enrich the MAIT cells. The percentages of each cell population and the mean fluorescence intensity (MFI) were analyzed using Flow Jo software.

RESULTS

MAIT cells were enriched in synovial fluid of PsA (4.29 ± 0.82%) compared to PBMC (1.04 ± 0.71). With stimulation, SFMC MAIT cells produced significantly more IL-17A (32.66 ± 4.01%) compared to that of RA (23.93 ± 2.81%, p < 0.05) and OA (5.02 ± 0.16%, p < 0.05). MAIT cells were predominantly CD8⁺ (>80%). Significant upregulation of IL-23R was noted in synovial fluid MAIT cells of PsA (24.97 ± 2.33%, p < 0.001) and RA (21.93 ± 2.29%, p < 0.001) compared to that of OA (2.13 ± 2.29). This IL-23R was functionally active as evidenced by profound mitotic effect in presence of rIL-23.

CONCLUSION

MAIT cells are poly functional; produce multiple cytokines (IL-17A, IFN-γ, TNF-α). Here, we demonstrated synovial fluid MAIT cells as a major source of IL-17A and majority of MAIT cells were CD8⁺. Functionally active IL-23R on these migrated MAIT cells brings a new dimension. They may not need MR1 associated activation rather lesional IL-23 in the synovium can independently regulate these critical Tc17 CD8⁺ MAIT cells. Thus, these cells likely to be a part of the IL-23/IL-17A cytokine network and play a critical role in the pathogenesis of PsA.

Aggregatibacter actinomycetemcomitans Leukotoxin (LtxA; Leukothera®): Mechanisms of Action and Therapeutic Applications

Aggregatibacter actinomycetemcomitans is an oral pathogen that produces the RTX toxin, leukotoxin (LtxA; Leukothera^®). A. actinomycetemcomitans is strongly associated with the development of localized aggressive periodontitis. LtxA acts as a virulence factor for A. actinomycetemcomitans to subvert the host immune response by binding to the β₂ integrin lymphocyte function-associated antigen-1 (LFA-1; CD11a/CD18) on white blood cells (WBCs), causing cell death. In this paper, we reviewed the state of knowledge on LtxA interaction with WBCs and the subsequent mechanisms of induced cell death. Finally, we touched on the potential therapeutic applications of LtxA (trade name Leukothera^®) toxin therapy for the treatment of hematological malignancies and immune-mediated diseases.

Increased risk of psoriasis in patients with chronic rhinosinusitis without nasal polyps: a longitudinal follow-up study using Korean national sample cohort

PURPOSE

Focal chronic inflammation or infection is thought to be one of the causes of psoriasis. Few reports on the association between chronic rhinosinusitis (CRS) and psoriasis exist, thus it is poorly defined. This study seeks to investigate the incidence of psoriasis in patients with CRS with reference to a matched control group.

METHODS

This national cohort study relies on data from Korean Health Insurance Review and Assessment Service-National Sample Cohort (HIRA-NSC), which were entered from 2002 to 2013. A total of 34,219 patients with CRS without nasal polyps was matched with 136,976 controls. The Cox proportional hazard model was used to analyze the crude (simple) and adjusted hazard ratios (HRs) of psoriasis. For subgroup analysis, participants were grouped by age and sex.

RESULTS

The risk of psoriasis was higher in the CRS group than in the control group (adjusted HR 1.28, 95% CI 1.12-1.47, P < 0.001). Children, adolescents below 19 years regardless of sex, and old adult men above 60 years are at significantly higher risk for subsequent psoriasis after CRS diagnosis.

CONCLUSION

CRS may increase the risk of psoriasis.

Adaptive and Innate Immunity in Psoriasis and Other Inflammatory Disorders

Over the past three decades, a considerable body of evidence has highlighted T cells as pivotal culprits in the pathogenesis of psoriasis. This includes the association of psoriasis with certain MHC (HLA) alleles, oligoclonal expansion of T cells in some cases, therapeutic response to T cell-directed immunomodulation, the onset of psoriasis following bone marrow transplantation, or induction of psoriasis-like inflammation by T cells in experimental animals. There is accumulating clinical and experimental evidence suggesting that both autoimmune and autoinflammatory mechanisms lie at the core of the disease. Indeed, some studies suggested antigenic functions of structural proteins, and complexes of self-DNA with cathelicidin (LL37) or melanocytic ADAMTSL5 have been proposed more recently as actual auto-antigens in some cases of psoriasis. These findings are accompanied by various immunoregulatory mechanisms, which we increasingly understand and which connect innate and adaptive immunity. Specific adaptive autoimmune responses, together with our current view of psoriasis as a systemic inflammatory disorder, raise the question of whether psoriasis may have connections to autoimmune or autoinflammatory disorders elsewhere in the body. While such associations have been suspected for many years, compelling mechanistic evidence in support of this notion is still scant. This review sets into context the current knowledge about innate and adaptive immunological processes in psoriasis and other autoimmune or autoinflammatory diseases.

Acute onset of psoriatic spondyloarthritis as a new manifestation of post-streptococcal reactive arthritis: a case series

Streptococcus is well associated with a myriad of inflammatory diseases. Among others, this bacterium is linked to the triggering of psoriasis and to post-streptococcal reactive arthritis (PSRA), an arthritis which is typically confined to peripheral joints. Three patients who developed acute psoriatic spondyloarthritis (SpA) following a recent streptococcal infection are described in this article. We searched the existing literature for cases of axial involvement in PSRA and reviewed the association between streptococcal infection and psoriasis or psoriatic arthritis )PsA). In all patients, psoriatic SpA occurred within 7-10 days of a confirmed streptococcal infection. The main presenting syndrome was inflammatory back pain with evidence of acute axial spondyloarthritis on magnetic resonance imaging. One patient had guttate psoriasis, the second patient developed pustular psoriasis, and the third patient had exacerbation of pustular palmoplantar psoriasis. Two patients required treatment with tumor necrosis factor alpha (TNF-α) blockers. Axial involvement in PSRA is very rare. A potential association of streptococcal infection and development of PsA has been explored in several articles. However, to the best of our knowledge, acute psoriatic SpA as a manifestation of PSRA has yet to be described. Acute psoriatic SpA should be considered in the differential diagnosis of new-onset inflammatory back pain followed by psoriasis in young adults who had a recent throat infection. KEY POINTS: • Our case series describes three cases of acute psoriatic spondyloarthritis that occurred within 7--10 days of a confirmed streptococcal infection and progressed to full blown chronic disease. • Acute psoriatic spondyloarthritis as a manifestation of post streptococcal reactive arthritis should be considered in the differential diagnosis of new onset inflammatory back pain followed by psoriasis in young adults who had a recent throat infection.

The contribution of IL-17 to the development of autoimmunity in psoriasis

Psoriasis is an (auto)immune-mediated disease that manifests as widespread desquamative erythema. The TNF-α/IL-23/IL-17A axis is crucial to its pathogenesis, which is demonstrated by its excellent therapeutic response to biologics that target this axis. There is a strong association between HLA-C*0602 and psoriasis, and researchers have identified autoantigens that are restricted to this major histocompatibility class I molecule. These auto-Ags include LL-37, A disintegrin and metalloprotease domain containing thrombospondin type 1 motif-like 5 (ADAMTSL5), and keratin 17. IL-17A-producing T cells have been identified in T cell populations that are reactive to these auto-Ags. In addition, lipid Ags have surfaced as candidate auto-Ags that activate IL-17A-producing T cells in a CD1a-restricted manner. In this article, we review the candidate auto-Ags that may contribute to the activation of the IL-17A-deviated immune response in psoriasis.

Dermal mesenchymal stem cells: a resource of migration-associated function in psoriasis?

BACKGROUND

Psoriasis is a chronic and systemic, immune-mediated, inflammatory disease. Mesenchymal stem cells have effects on the inflammatory microenvironment, including regulating the proliferation, differentiation, recruitment, and migration of immunocytes.

METHODS

To investigate whether dermal mesenchymal stem cells (DMSCs) may act on migration of immunocytes in psoriasis patients, 22 patients with psoriasis and 22 matching healthy controls (age and sex in this study) were recruited. Seven migration-associated genes including chemokine like receptor-1 (CMKLR-1), collagen type VIII alpha1 (COL8A-1), neuropilin and tolloid-like 2 (NETO-2), nik-related kinase (NRK), secreted frizzled-related protein (SFRP), sulfate 6-O-endosulfatase 2 (SULF-2), and synaptotagmin-like protein 2 (SYTL-2) were analyzed by quantitative real-time reverse transcription PCR and western blot. Peripheral blood-derived mononuclear cells (PBMCs) migration to MSCs was measured using a Thanswell chamber system.

RESULTS

We observed the upregulation of CMKLR-1, COL8A-1, NETO-2, NRK, SYTL-2, and SULF-2 in dermal mesenchymal stem cells derived from patients with psoriasis at both mRNA and protein level, however, a significant downregulation of SFRP-2 between two groups. By contrast, there were no significant between-group differences at the mRNA and protein expression level of NETO-2 and SULF-2. The migration assay showed that in vitro the normal PBMC migration to psoriatic DMSC group was a 6.3 ± 0.7-fold increase compared with the control group.

CONCLUSIONS

The results may suggest a potential pathogenetic involvement of DMSCs on migration of monocytes in psoriasis. Immune responses are regulated at the level of DMSCs, which probably represent the cells primarily involved in the "psoriatic march."

Bystander T Cells: A Balancing Act of Friends and Foes

T cell responses are essential for appropriate protection against pathogens. T cell immunity is achieved through the ability to discriminate between foreign and self-molecules, and this relies heavily on stringent T cell receptor (TCR) specificity. Recently, bystander activated T lymphocytes, that are specific for unrelated epitopes during an antigen-specific response, have been implicated in diverse diseases. Numerous infection models have challenged the classic dogma of T cell activation as being solely dependent on TCR and major histocompatibility complex (MHC) interactions, indicating an unappreciated role for pathogen-associated receptors on T cells. We discuss here the specific roles of bystander activated T cells in pathogenesis, shedding light on the ability of these cells to modulate disease severity independently from TCR recognition.

Psoriasis, chronic tonsillitis, and biofilms: Tonsillar pathologic findings supporting a microbial hypothesis

Group A Streptococcus has been identified as a possible etiologic agent in psoriasis in epidemiologic, immunologic, immunopathologic, medical, and surgical studies. Tonsillectomy has been shown to provide considerable relief to 75% of patients with plaque psoriasis. Even with the substantial evidence supporting group A Streptococcus as a causative pathogen in psoriasis, it is an elusive pathogen because it is not culturable, nor does it exhibit any positive serologic evidence of its presence. One possible reason for the negative cultures and negative serology findings with group A Streptococcus is the development of biofilms. We conducted a pathologic study to determine whether biofilms were present in the tonsillar tissues of 10 patients with psoriasis-6 men and 4 women, aged 25 to 64 years (mean: 48)-and in 10 age- and sex-matched controls with chronic tonsillitis who did not have psoriasis. We found that biofilms were present in every tonsillectomy specimen we examined, including those of the controls. Whereas psoriasis has been considered a "double hit" phenomenon, we believe that the development of skin lesions is likely attributable to the presence of the gene PSORS together with the biofilm in psoriasis patients rather than to the biofilm itself. Biofilms have been identified in both extra- and intracellular locations. We believe our findings add further evidence supporting a microbial pathogenesis of this disease.