Oligoclonal expansion of intraepidermal T cells in psoriasis skin lesions

T-Cell‒Mediated Autoimmunity: Mechanisms and Future Directions

T cells are key drivers of autoimmunity in numerous noncommunicable inflammatory skin diseases by directly harming host tissue or through helping B cells in producing autoantibodies. Technological advances have contributed to identifying autoantigens, the Holy Grail of autoimmunity, in many inflammatory disorders of the skin. Novel therapeutic approaches such as chimeric (auto)antibody receptor T cells are a milestone on the way to finding individualized, well-tolerated, targeted therapies. This review summarizes the current knowledge on pathogenesis, immune response pattern‒related ontology, diagnostic approaches, and treatment options of autoimmune skin diseases.

Psoriasis and Cardiometabolic Diseases: The Impact of Inflammation on Vascular Health

Psoriasis is a common chronic inflammatory condition associated with a higher risk of cardiovascular disease. Psoriasis confers a dose-dependent increase in risk for the metabolic syndrome and its components. The metabolic syndrome and its components have been associated with higher coronary atherosclerosis in psoriasis and cardiovascular events in the general population. In this review, we discuss the role of inflammation and psoriasis in cardiometabolic diseases with a focus on the metabolic syndrome and its components. We highlight the relationship between psoriasis and important cardiovascular risk factors encompassed by obesity, dyslipidemia, insulin resistance and hypertension. Furthermore, we briefly highlight literature on anti-inflammatory therapies and their impact on the components of the metabolic syndrome as well as directly quantified coronary atherosclerosis burden.

PD-1 Expression Defines Epidermal CD8+CD103+ T Cells Preferentially Producing IL-17A and Using Skewed TCR Repertoire in Psoriasis

In psoriasis, CD8⁺CD103⁺ memory T cells residing in the epidermis represent an effector population capable of maintaining the condition and driving a recurrence of the disease. Tissue-infiltrating CD8⁺ T cells expressing PD-1 are regarded as antigen-primed effector cells in others chronic inflammatory diseases. However, the expression and significance of PD-1 on skin-infiltrating CD8⁺ T cells in human psoriasis is not known. By analyzing skin-infiltrating T cells from human psoriasis, we found that active psoriatic epidermis contained PD-1 expressing CD8⁺CD103⁺ T cells that correlated with the disease severity and histopathology. PD-1⁺CD8⁺CD103⁺ T cells possessed a canonical psoriasis-specific resident memory phenotype with IL-23R expression and produced IL-17A, whereas PD-1^-CD8⁺CD103⁺ T cells preferentially produced IFN-γ. The diversity of skin-infiltrating T cells was dominated by CD4⁺ T cells, while CD8⁺ T cells, especially CD8⁺CD103⁺T cells, represented an oligoclonal population in active psoriasis. In addition, PD-1⁺CD8⁺CD103⁺T cells used different TCR Vβs from PD-1^-CD8⁺CD103⁺T cells counterpart. In the early resolved lesion, the composition and functional status of PD-1⁺CD8⁺CD103⁺T cells were markedly altered, while PD-1^-CD8⁺CD103⁺ T cells population was minimally changed. Collectively, PD-1 expression delineates a putative pathogenic subset of epidermal CD8⁺CD103⁺ T cells, which possibly play a role in psoriasis pathogenesis.

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.

T Cell Hierarchy in the Pathogenesis of Psoriasis and Associated Cardiovascular Comorbidities

The key role of T cells in the pathogenesis of cutaneous psoriasis has been well described in the last decade and the knowledge of the relative role of the different subsets of T cells in psoriasis pathogenesis has considerably evolved. Now, it is clear that IL-17A-producing T cells, including Th17/Tc17, have a central role in the pathogenesis of cutaneous psoriasis and therapies blocking the IL-17A pathway show high clinical efficacy. By contrast, the contribution of IFNγ-producing T cells has progressively become less clear because of the lack of efficacy of anti-IFNγ antibodies in clinical studies. In parallel, the role of CD8⁺ T cells specific for self-antigens has been revived and increasing evidence now indicates that in psoriatic skin the majority CD8⁺ T cells are present in the form of epidermal tissue-resident memory T cells. In the last years it also emerged the possibility of a contribution of T cell recirculation in the pathogenesis of psoriasis and its systemic manifestations. The aim of this review is to define a hierarchy for the different subsets of T cells in the T cell-mediated inflammatory cascade in psoriatic skin. This analysis will possibly help to distinguish the subsets that initiate the disease, those involved in the establishment of the self-sustaining amplification loop that leads to the cutaneous clinical manifestations and finally the subsets that act as downstream players in established lesions. Specific T cell subpopulations finally will be considered for their possible role in propagating inflammation at distant sites and for representing a link with systemic inflammation and cardiovascular comorbidities.

Psoriasis: a mixed autoimmune and autoinflammatory disease

In recent years marked progress has been made in our understanding of the critical biologic and immunologic pathways involved in psoriasis. Genetic studies have demonstrated that susceptibility to psoriasis involves components of both the adaptive and innate immune system and not surprisingly activation of both of these arms of the immune system is found in psoriatic skin. While adaptive immune responses predominate in chronic plaque psoriasis, innate and autoinflammatory responses dominate in pustular forms of psoriasis, with other clinical subtypes extending on a spectrum between plaque and pustular psoriasis. This makes psoriasis a unique disease where both autoimmune and autoinflammatory responses co-exist, with the balance between the two being critical in shaping its clinical presentation.

TCR sequencing facilitates diagnosis and identifies mature T cells as the cell of origin in CTCL

Early diagnosis of cutaneous T cell lymphoma (CTCL) is difficult and takes on average 6 years after presentation, in part because the clinical appearance and histopathology of CTCL can resemble that of benign inflammatory skin diseases. Detection of a malignant T cell clone is critical in making the diagnosis of CTCL, but the T cell receptor γ (TCRγ) polymerase chain reaction (PCR) analysis in current clinical use detects clones in only a subset of patients. High-throughput TCR sequencing (HTS) detected T cell clones in 46 of 46 CTCL patients, was more sensitive and specific than TCRγ PCR, and successfully discriminated CTCL from benign inflammatory diseases. HTS also accurately assessed responses to therapy and facilitated diagnosis of disease recurrence. In patients with new skin lesions and no involvement of blood by flow cytometry, HTS demonstrated hematogenous spread of small numbers of malignant T cells. Analysis of CTCL TCRγ genes demonstrated that CTCL is a malignancy derived from mature T cells. There was a maximal T cell density in skin in benign inflammatory diseases that was exceeded in CTCL, suggesting that a niche of finite size may exist for benign T cells in skin. Last, immunostaining demonstrated that the malignant T cell clones in mycosis fungoides and leukemic CTCL localized to different anatomic compartments in the skin. In summary, HTS accurately diagnosed CTCL in all stages, discriminated CTCL from benign inflammatory skin diseases, and provided insights into the cell of origin and location of malignant CTCL cells in skin.

The antimicrobial peptide LL37 is a T-cell autoantigen in psoriasis

Psoriasis is a common T-cell-mediated skin disease with 2-3% prevalence worldwide. Psoriasis is considered to be an autoimmune disease, but the precise nature of the autoantigens triggering T-cell activation remains poorly understood. Here we find that two-thirds of patients with moderate-to-severe plaque psoriasis harbour CD4(+) and/or CD8(+) T cells specific for LL37, an antimicrobial peptide (AMP) overexpressed in psoriatic skin and reported to trigger activation of innate immune cells. LL37-specific T cells produce IFN-γ, and CD4(+) T cells also produce Th17 cytokines. LL37-specific T cells can infiltrate lesional skin and may be tracked in patients blood by tetramers staining. Presence of circulating LL37-specific T cells correlates significantly with disease activity, suggesting a contribution to disease pathogenesis. Thus, we uncover a role of LL37 as a T-cell autoantigen in psoriasis and provide evidence for a role of AMPs in both innate and adaptive immune cell activation.

Molecular pathophysiology of psoriasis and molecular targets of antipsoriatic therapy

Psoriasis is a chronic inflammatory skin disease characterised by elevated red scaly plaques on specific body sites. Histologically, the plaques are defined by epidermal hyperplasia, epidermal and dermal infiltration by leukocytes, and changes in the dermal microvasculature. Differentiation and activation are disturbed in lesional psoriatic keratinocytes, and the pool of proliferating keratinocytes is increased, which is accompanied by enhanced production of proinflammatory cytokines, adhesion molecules and antimicrobial peptides. These changes in psoriatic keratinocytes are caused by altered expression of genes associated with epidermal differentiation, and by activation of signalling pathways involving signal transducer and activator of transcription 3 (STAT3), type I interferon (IFN) and mitogen-activated protein kinase (MAPK). The number of T cells, and myeloid and plasmacytoid dendritic cells (DCs) is markedly increased in psoriatic lesions. Myeloid DCs produce interleukin (IL)-23, tumour necrosis factor (TNF)-alpha and inducible nitric oxide synthase (iNOS), which are crucial cytokines in the pathogenesis of psoriasis. IL-23 stimulates the secretion of IL-22 by T helper 17 cells, and IL-22 induces epidermal hyperplasia. The crosstalk between keratinocytes and leukocytes via their proinflammatory cytokines creates the vicious circle of chronic skin inflammation seen in psoriasis. This suggests that optimal treatment of psoriasis needs to target pathogenic pathways in both leukocytes and keratinocytes.

Molecular dissection of psoriasis: integrating genetics and biology

Psoriasis is a common and debilitating disease of the skin, nails, and joints, with an acknowledged but complex genetic basis. Early genome-wide linkage studies of psoriasis focused on segregation of microsatellite markers in families; however, the only locus consistently identified resided in the major histocompatibility complex. Subsequently, several groups mapped this locus to the vicinity of HLA-C, and two groups have reported HLA-Cw6 itself to be the major susceptibility allele. More recently, the development of millions of single-nucleotide polymorphisms, coupled with the development of high-throughput genotyping platforms and a comprehensive map of human haplotypes, has made possible a genome-wide association approach using cases and controls rather than families. Taking advantage of these developments, we participated in a collaborative genome-wide association study of psoriasis involving thousands of cases and controls. Initial analysis of these data revealed and/or confirmed association between psoriasis and seven genetic loci-HLA-C, IL12B, IL23R, IL23A, IL4/IL13, TNFAIP3, and TNIP1-and ongoing studies are revealing additional loci. Here, we review the epidemiology, immunopathology, and genetics of psoriasis, and present a disease model integrating its genetics and immunology.

Psoriasis--as an autoimmune disease caused by molecular mimicry

Psoriasis is strongly associated with streptococcal throat infection, and patients have increased occurrence of such infections. Psoriatic lesional T cells are oligoclonal, and T cells recognizing determinants common to streptococcal M-protein and keratin have been detected in patients' blood. We propose that CD8(+) T cells in psoriatic epidermis respond mainly to such determinants, whereas CD4(+) T cells in the dermis preferentially recognize determinants on the streptococcal peptidoglycan that might itself act as an adjuvant. The streptococcal association might reflect the concurrence of superantigen production promoting skin-homing of tonsil T cells, M-protein mimicking keratin determinants, and adjuvant effects of the peptidoglycan. Accordingly, improvement of psoriasis after tonsillectomy should be associated with fewer T cells that recognize keratin and streptococcal determinants.

Genome-wide association scan yields new insights into the immunopathogenesis of psoriasis

Psoriasis is a common, immunologically mediated, inflammatory and hyperproliferative disease of the skin and joints, with a multifactorial genetic basis. We earlier mapped PSORS1, the major psoriasis susceptibility gene in the major histocompatibility complex (MHC), to within or very near HLA-Cw6. In an effort to identify non-MHC psoriasis genes, we carried out a collaborative genome-wide association study. After the initial follow-up genotyping of 21 single nucleotide polymorphisms from 18 loci, showing strong evidence of association in the initial scan, we confirmed evidence of association at seven loci. Three of these loci confirm earlier reports of association (HLA-C, IL12B, IL23R) and four identify novel signals located near plausible candidate genes (IL23A, IL4/IL13, TNFAIP3 and TNIP1). In other work, we have also shown that interferon-gamma (IFN-gamma) treatment induces interleukin (IL)-23 mRNA and protein in antigen-presenting cells (APC), leading to the proliferation of CD4+ and CD8+ memory T cells expressing IL-17. Although functional variants remain to be identified, we speculate that genetic variants at the IL4/IL13 locus contribute to the Th1 bias that is characteristic of psoriasis, that Th1-derived IFN-gamma supports expansion of IL-17+ T cells through APC-derived IL-23 and that negative regulation of inflammatory signaling through the NF-kappaB axis is impaired because of genetic variants of TNFAIP3 and TNIP1.

In vivo dynamics of intraepidermal CD8+ T cells and CD4+ T cells during the evolution of fixed drug eruption

BACKGROUND

Although a severe form of fixed drug eruption (FDE) clinically and histologically mimics toxic epidermal necrolysis (TEN), subsequent evolution of the two conditions is quite different. It remains unknown, however, which factors determine whether these lesions resolve spontaneously or subsequently progress to TEN.

OBJECTIVES

Because epidermal injury in TEN can be locally reproduced in the evolving FDE lesions, we sought to investigate how epidermal damage can be induced in the evolving FDE lesions and how disease progression to TEN can be prevented, by analysing the FDE lesions induced by clinical challenge with the causative drug.

METHODS

We immunohistochemically investigated in vivo dynamics of T-cell trafficking and activation that occur in the evolving FDE lesions using sequential biopsy specimens obtained at multiple time points from the FDE lesions.

RESULTS

Intraepidermal CD8+ T cells, which are resident in the lesional epidermis as a stable homogeneous population of memory T cells, transiently acquire a natural killer-like phenotype and express cytotoxic granules upon activation. The influx into the epidermis of CD4+ T cells including Foxp3+ regulatory T cells (Tregs) during the evolution serves to ameliorate epidermal damage induced by activation of the intraepidermal CD8+ T cells. Interleukin-15 derived from the lesional epidermis could maintain the survival of the intraepidermal CD8+ T cells even in the absence of antigenic stimulus over a prolonged period of time (> 4 years).

CONCLUSIONS

Whether Tregs could migrate to the lesions upon activation of intraepidermal CD8+ T cells would determine whether the inflammation becomes resolved spontaneously or progresses to TEN.

Immunopathogenesis of psoriasis

Investigations into the cause and treatment of psoriasis remain at the forefront of basic and applied clinical research efforts around the world. The purpose for this review is to provide an up-to-date synopsis of recent progress in ten sections exploring the immunological and inflammatory basis for psoriasis. Given the breadth of this topic in investigative skin biology and frequent paradigm shifts, it should not be surprising that the bibliography contains more than 150 references; many of which have been published in the last 5 years. Whereas considerable progress has been made into the immunopathogenesis of psoriasis, many fundamentally important questions remain regarding the role of cells located in both epidermal and dermal compartments. Attempts to characterize various animal models of psoriasis, delineation of the mechanism of action for biological agents, and consideration of molecular links between skin inflammation and various extracutaneous comorbidities are likely to continue challenging investigators and clinicians for many years to come.

Psoriasis: the epidermal component

Besides the infiltrate of immune cells in psoriatic lesions, the principal characteristic changes in the skin are changes of the epidermal architecture and alterations of keratinocyte differentiation, which are distinct from other inflammatory skin diseases clinically and histologically. Several lines of evidence suggest that 3 of the 9 psoriasis susceptibility loci identified today might play a role in the keratinocyte differentiation program. Therefore, besides the dysregulation of the immune system, intrinsic epidermal components are also likely to play a role in triggering and/or sustaining the disease process and contribute to the chronicity of psoriasis and its frequent relapses.

Effect of PUVA, narrow-band UVB and cyclosporin on inflammatory cells of the psoriatic plaque

BACKGROUND

Because antigen presenting is necessary for T-cell activation, antigen-presenting cells should be involved in the pathogenesis of psoriasis. In this study, our purpose was to evaluate and compare effects of PUVA, cyclosporine A and narrow-band UVB on dendritic cells and activated lymphocytes in the psoriatic lesions.

METHODS

Forty-five volunteered patients (15 patients in each treatment group as PUVA, cyclosporin A and narrow-band UVB) were enrolled in this study. Lesional skin biopsies were taken from each patient before and after treatments. Fresh frozen biopsies were studied for the expressions of CD1a, CD68, CD86, CD4, CD8 and HLA-DR proteins by immunohistochemistry.

RESULTS

There was no correlation between severity of the lesions and expressions of the antigens. Only PUVA significantly decreased CD1a+ epidermal Langerhans cells' (LCs) counts. Treatment modalities decreased expression of costimulator CD86, and most of them decrease antigen-presenting capacity of skin by decreasing HLA class-II expression.

CONCLUSIONS

All treatment modalities equally reduce lymphocytes, macrophages and dendritic cells. PUVA is the only treatment that decreases epidermal LCs. All treatments effectively diminish expression of CD86 and inhibit this step of inflammation.

HLA-C expression pattern is spatially different between psoriasis and eczema skin lesions

Interactions between genetic and environmental factors underlie the immune dysregulation and keratinocyte abnormalities that characterize psoriasis. Among known psoriasis susceptibility loci (PSORS), PSORS1 on chromosome 6 has the strongest association to disease. Altered expression of some PSORS1 candidate genes has been reported but little is known about HLA-C expression in psoriasis. This study compared expression of major histocompatibility complex class Ia and HLA-C in psoriasis, allergic contact eczema, and normal skin. Although HLA-C was abundant in protein extracts from both eczema and psoriasis, a consistent and intriguing difference in the expression pattern was observed; strong immunoreactivity in the basal cell layer, polarized towards the basement membrane in psoriasis, whereas in eczema lesions HLA-C immunostaining was present mostly in suprabasal cells. Inflammatory cells in the dermis were strongly stained in both diseases. Normal skin epithelium showed less intense but similar HLA-C staining as eczema lesions. HLA class Ia expression overall resembled that of HLA-C in all samples. The distinct HLA-C expression patterns in psoriasis and eczema suggest a functional role in the specific psoriasis immune response and not only a general feature of inflammation.

Sequence and haplotype analysis supports HLA-C as the psoriasis susceptibility 1 gene

Previous studies have narrowed the interval containing PSORS1, the psoriasis-susceptibility locus in the major histocompatibility complex (MHC), to an approximately 300-kb region containing HLA-C and at least 10 other genes. In an effort to identify the PSORS1 gene, we cloned and completely sequenced this region from both chromosomes of five individuals. Two of the sequenced haplotypes were associated with psoriasis (risk), and the other eight were clearly unassociated (nonrisk). Comparison of sequence of the two risk haplotypes identified a 298-kb region of homology, extending from just telomeric of HLA-B to the HCG22 gene, which was flanked by clearly nonhomologous regions. Similar haplotypes cloned from unrelated individuals had nearly identical sequence. Combinatorial analysis of exonic variations in the known genes of the candidate interval revealed that HCG27, PSORS1C3, OTF3, TCF19, HCR, STG, and HCG22 bore no alleles unique to risk haplotypes among the 10 sequenced haplotypes. SPR1 and SEEK1 both had messenger RNA alleles specific to risk haplotypes, but only HLA-C and CDSN yielded protein alleles unique to risk. The risk alleles of HLA-C and CDSN (HLA-Cw6 and CDSN*TTC) were genotyped in 678 families with early-onset psoriasis; 620 of these families were also typed for 34 microsatellite markers spanning the PSORS1 interval. Recombinant haplotypes retaining HLA-Cw6 but lacking CDSN*TTC were significantly associated with psoriasis, whereas recombinants retaining CDSN*TTC but lacking HLA-Cw6 were not associated, despite good statistical power. By grouping recombinants with similar breakpoints, the most telomeric quarter of the 298-kb candidate interval could be excluded with high confidence. These results strongly suggest that HLA-Cw6 is the PSORS1 risk allele that confers susceptibility to early-onset psoriasis.

The Vast Majority of CLA+ T Cells Are Resident in Normal Skin

There are T cells within normal, noninflamed skin that most likely conduct immunosurveillance and are implicated in the development of psoriasis. We isolated T cells from normal human skin using both established and novel methods. Skin resident T cells expressed high levels of CLA, CCR4, and CCR6, and a subset expressed CCR8 and CXCR6. Skin T cells had a remarkably diverse TCR repertoire and were mostly Th1 memory effector cells with smaller subsets of central memory, Th2, and functional T regulatory cells. We isolated a surprising number of nonexpanded T cells from normal skin. To validate this finding, we counted T cells in sections of normal skin and determined that there are approximately 1 x 10(6) T cells/cm(2) normal skin and an estimated 2 x 10(10) T cells in the entire skin surface, nearly twice the number of T cells in the circulation. Moreover, we estimate that 98% of CLA(+) effector memory T cells are resident in normal skin under resting conditions. These findings demonstrate that there is a large pool of memory T cells in normal skin that can initiate and perpetuate immune reactions in the absence of T cell recruitment from the blood.

Expression of cutaneous lymphocyte-associated antigen (CLA) in tonsillar T-cells and its induction by in vitro stimulation with alpha-streptococci in patients with pustulosis palmaris et plantaris (PPP)

Pustulosis palmaris et plantaris (PPP) is known to be a one of the tonsil-related diseases because tonsillectomy is quite effective in curing this condition. However etiological association between tonsils and PPP have not fully clarified yet. Cutaneous lymphocyte-associated antigen (CLA) is known to be a specific homing receptor that facilitates T-cell migration into skin. In this study, we investigated the expression of CLA on T-cells in tonsil, peripheral blood, and skin from patients with PPP. Two-color flow cytometric and two-color immunohistological analyses revealed that the numbers of CLA/CD3 double-positive cells in freshly isolated tonsillar mononuclear cells (TMC) and in tonsillar tissues were significantly higher in patients with PPP than in patients without PPP (P<0.01, each). In vitro stimulus with alpha-streptococcal antigens enhanced CLA expression of tonsillar T-cells and TGF-beta production of TMC in patients with PPP (P<0.01, each), but did not in patients without PPP. In peripheral blood from PPP patients, the number of the CLA/CD3 double-positive cells significantly decreased at 6 months after tonsillectomy (P<0.05). The CLA/CD3 double-positive cells and the postcapillary venule that expressed with a ligand of CLA, E-selectin, were found more frequently in the plantar skin from patients with PPP as compared to that from healthy volunteers (P<0.01, each). These data suggest that a novel immune response to alpha-streptococci may enhance CLA expression on tonsillar T-cells through TGF-beta production in patients with PPP, resulting in moving of CLA-positive tonsillar T-cells to skin and tissue damages. This may play a key role in pathogenesis of PPP.

Upregulation of the IFN-gamma-stimulated genes in the development of delayed pigmented spots on the dorsal skin of F1 mice of HR-1 x HR/De

DNA microarray hybridization was used to measure the changes of mRNA levels over time during the development of delayed pigmented spots on the dorsal skin of F1 mice of HR-1 x HR/De. Upregulation of a number of interferon (IFN)-gamma-stimulated genes was detected in delayed pigmented lesions, suggesting that IFN-gamma may play a pivotal role in the development of delayed pigmented spots in this model. Upregulation of these genes was further supported by the increased protein expression level of IFN-gamma in the lesions. Epidermal infiltration of CD8(+) T lymphocytes and mast cell accumulation in the dermis were observed in delayed pigmented spots. Genes encoding chemokines such as monocyte chemoattractant protein-2 (MCP-2), IFN-inducible protein 10 (IP-10), and monokine induced by IFN-gamma (MIG) were among those upregulated by IFN-gamma. We hypothesize that chemokines produced in the epidermis induce migration of inflammatory cells, such as T lymphocytes, mast cells, and macrophages, to the vicinity of melanocytes. Keratinocytes, T lymphocytes, mast cells, and macrophages would become involved in an interactive network, providing a suitable local environment for melanocyte activation. In this environment, melanocytes are exposed to an extensive array of secreted mediators. Reciprocal activation among these cells to maintain this interactive network results in constitutive melanocyte activation and chronic melanin synthesis in delayed pigmented lesions.

Analysis of T cell receptor alpha-chain variable region (Valpha) usage and CDR3alpha of T cells infiltrated into lesions of psoriasis patients

Psoriasis is a common inflammatory skin disease and is considered as T cell-mediated immune response. In this study, we analyzed T cell receptor alpha-chain variable region (TCR Valpha) usage in the lesions of psoriasis patients using 5'-RACE. As the results, Valpha1, -2, -7, -8, -10, -11, -12, and -23 were commonly detected in psoriatic lesions and comparison of expressions of these Valpha types between psoriasis patients and healthy individuals showed that Valpha1, -7, -11, and -12 were highly increased in psoriasis patients than in healthy individuals. Compared with atopy dermatitis patients, the expressions of Valpha1 and Valpha7 were increased in psoriasis patients. Then, to identify CDR3alpha of T cells infiltrated in psoriatic lesions, we examined which type of J gene segment was rearranged with Valpha1 or Valpha7, which the expressions was specifically increased in psoriatic lesions. The result showed that the V-J rearrangements between the examined patients were not equivalent and their frequencies were diverse, however, several common rearrangements such as Valpha1-Jalpha13, -23, -27, or -34 and Valpha7-Jalpha12, -33 were detected. The results in this study might provide the clue to define the characteristics of T cells associated with the pathogenesis of psoriasis.

Alefacept reduces infiltrating T cells, activated dendritic cells, and inflammatory genes in psoriasis vulgaris

Psoriasis vulgaris, a skin disease that is considered to be the result of a type 1 autoimmune response, provides an opportunity for studying the changes that occur in a target-diseased tissue during innovative immunotherapies. To gain a more comprehensive picture of the response to an approved biological therapy, we studied alfacept, which is a CD2 binding fusion protein. We examined T cells, dendritic cells (DCs), and expression of a number of inflammatory genes. In 22 patients, 55% demonstrated a clear histological remission of the disease, with a 73% reduction in lesional lymphocytes and a 79% decrease in infiltrating CD8+ cells. Only histological responders showed marked reductions in the tissue expression of inflammatory genes IFN-gamma, signal transducer and activator of transcription 1, monokine induced by IFN-gamma, inducible NO synthase, IL-8, and IL-23 subunits. Parallel decreases in CD83+ and CD11c+ DCs also were measured by immunohistochemistry. Because we observed that alefacept binds primarily to T cells and not DCs, we suggest that T cells are the primary target for therapy, but that DCs and a spectrum of type 1 inflammatory genes are coordinately suppressed.

Psoriasis vulgaris: an interplay of T lymphocytes, dendritic cells, and inflammatory cytokines in pathogenesis

PURPOSE OF REVIEW

Discuss and update concepts and hypotheses for the pathogenesis of psoriasis based on new research reports (primarily from 2003 and early 2004).

RECENT FINDINGS

Increases in newly defined dendritic cell subsets, cytokines, and chemokines have been identified in psoriasis lesions and have modified views of T-cell-mediated pathogenesis. In addition, the psoriasis transcriptome has been defined by large-scale genomic expression studies, and these data suggest distinct molecular mechanisms of type 1 T-cell-mediated inflammation. Somewhat surprisingly, therapeutic clinical trials suggest that tumor necrosis factor is a major pathogenic cytokine in psoriasis, whereas translational studies point to roles of other innate pathways mediated by heat shock proteins, glycolipids, natural killer T cells, or dendritic cells in disease pathogenesis.

SUMMARY

An interactive network of inflammatory cytokines, chemokines, dendritic cells, and type 1 T cells or natural killer T cells potentially drives pathogenic inflammation in psoriasis vulgaris. Continued clinical studies with defined immune antagonists provide a critical means to dissect the contribution of different cell subsets and genomic pathways to the pathogenesis of psoriasis vulgaris.

Current concepts in the immunopathogenesis of psoriasis

There is much evidence to support the concept that psoriasis is a type 1 autoimmune disease, primarily mediated by interferon gamma and other inflammatory cytokines. There has been renewed interest in the role of components of the innate immune system, however,and it may be that overlap between the innate and acquired arms of the immune system can better explain immunopathogenesis in psoriasis. Relevant cell types, receptors, and immune mediators within these traditional boundaries of the immune system are discussed.Finally, pathogenic contributions from important psoriatic mouse models and recent genomic data using the new gene chip technology are elaborated.

Correlation of psoriasis activity with abundance of CD25+CD8+ T cells: conditions for cloning T cells from psoriatic plaques

The role of T cells in the pathogenesis of psoriasis is widely acknowledged. However, key aspects of their precise function in the disease as well as the relative pathogenic contribution of T-cell subsets are still unknown. T-cell clones have been isolated from psoriatic plaques but a study of conditions affecting the isolation and expansion of T-cell clones from psoriatic skin has not been reported to date. Here, we observe a correlation of disease activity with the frequency of the CD3(+)CD8(+)CD25(+) subset. We show that prolonged in vitro culture changes the phenotypic subset distribution of T-cell lines derived from psoriatic skin and that T-cell clones can be isolated by sorting of CD25(+) cells emigrated from skin fragments after 7 days. We evaluate various conditions affecting expansion of psoriatic T-cell clones in vitro and show that blocking apoptosis can facilitate proliferation of activated T-cell clones in vitro. Our results indicate a prominent role of the CD8(+)CD25(+) T-cell subset in disease pathogenesis and should be useful in the design of experiments aiming at a systematic analysis of the specificity of clones present in psoriatic plaques.

CD4+ T cell-associated pathophysiology critically depends on CD18 gene dose effects in a murine model of psoriasis

In a CD18 hypomorphic polygenic PL/J mouse model, the severe reduction of CD18 (beta(2) integrin) to 2-16% of wild-type levels leads to the development of a psoriasiform skin disease. In this study, we analyzed the influence of reduced CD18 gene expression on T cell function, and its contribution to the pathogenesis of this disease. Both CD4(+) and CD8(+) T cells were significantly increased in the skin of affected CD18 hypomorphic mice. But only depletion of CD4(+) T cells, and not the removal of CD8(+) T cells, resulted in a complete clearance of the psoriasiform dermatitis. This indicates a central role of CD4(+) T cells in the pathogenesis of this disorder, further supported by the detection of several Th1-like cytokines released predominantly by CD4(+) T cells. In contrast to the CD18 hypomorphic mice, CD18 null mutants of the same strain did not develop the psoriasiform dermatitis. This is in part due to a lack of T cell emigration from dermal blood vessels, as experimental allergic contact dermatitis could be induced in CD18 hypomorphic and wild-type mice, but not in CD18 null mutants. Hence, 2-16% of CD18 gene expression is obviously sufficient for T cell emigration driving the inflammatory phenotype in CD18 hypomorphic mice. Our data suggest that the pathogenic involvement of CD4(+) T cells depends on a gene dose effect with a reduced expression of the CD18 protein in PL/J mice. This murine inflammatory skin model may also have relevance for human polygenic inflammatory diseases.

Immunopathogenic mechanisms in psoriasis

Psoriasis is a common autoimmune skin disease characterized by T cell-mediated hyperproliferation of keratinocytes. The disease has a strong but complex genetic background with a concordance of approximately 60% in monozygotic twins, and recent linkage and high resolution association studies indicate that HLA-Cw*0602 is itself a major susceptibility allele for psoriasis. Patients carrying this allele have been shown to have different clinical features and earlier age of disease onset, and patients homozygous for this allele have about 2.5 times higher disease risk than heterozygotes. Published data indicate that CD8+ T cells may play a major effector role in psoriasis. Epidermal infiltration of predominantly oligoclonal CD8+ T cells, and probably also of CD4+ T cells in the dermis, is a striking feature of chronic psoriasis lesions, indicating that these cells are responding to specific antigens. We argue that CD4+ T cells are essential for initiating and maintaining the pathogenic process of psoriasis but that cross-primed CD8+ T cells are the main effector cells responding to antigens in the HLA-Cw*0602 binding pocket of keratinocytes. It is further proposed that CD8+ T cells are involved in the control of the Th1 polarization, which is observed in psoriasis lesions, through a complex interplay between CD4+, CD8+ T cells and cross-presenting dendritic cells. It is also suggested that spontaneous remissions or fluctuations in disease activity may be determined by a balance within the lesions between effector and suppressor CD4+ and CD8+ T cells.

Immunpathogenese der Psoriasis. Immunopathogenesis of Psoriasis

Psoriasis is a chronic inflammatory disease of the skin and the joints. Multiple factors contribute to the initiation of psoriasis. They include specific genetic characteristics such as major histocompatibility antigens and psoriasis susceptibility genes, as well as trigger factors, namely streptococcal infections. Today, psoriasis is considered as a T-lymphocyte mediated autoimmune disease, even though the putative autoantigen remains unknown. Bacterial proteins with similarity to structural proteins of keratinocytes are potential target antigens. As in other autoimmune diseases, inflammatory cytokines of the innate immune system initiate a cascade that activates inflammation locally in the skin, in the circulation and most likely also in lymph nodes. IFN-gamma-producing CD4+ Th1-lymphocytes seem to be of central importance in the pathogenesis of psoriasis as they critically influence differentiation and functioning of antigen presenting cells, mast cells, neutrophils and endothelial cells. This inflammatory cascade simultaneously provokes neoangiogenesis in the dermis and proliferation of keratinocytes. Based on this hypothesis, cytokines or anticytokine antibodies that either inhibit T-cell mediated inflammation or transform disease-inducing, pro-inflammatory Th1-lymphocytes into a phenotype with anti-inflammatory properties were tested in psoriasis. As both approaches improved psoriasis, they strongly support the current concept that views psoriasis as a Th1-lymphocyte mediated disease.

Identification of a commonly used CDR3 region of infiltrating T cells expressing Vbeta13 and Vbeta15 derived from psoriasis patients

Psoriasis is a common inflammatory skin disease that is thought to be mediated by activated T cells. In this study, the complementarity-determining region 3 (CDR3) in T cell receptors was examined for a common sequence motif among the T cells infiltrated in psoriatic lesional skin. A common specific CDR3 motif (Vbeta13-DWTSGV-Jbeta2.7) in lesions from psoriasis patients was identified by polymerase-chain-reaction-based spectratyping analysis and DNA sequencing. In addition, VDJ rearrangement with highly homologous amino acid composition in the CDR3 was observed in Vbeta15 of T cell receptors in lesions derived from psoriatic patients. Remarkably, T cell receptors containing the Vbeta13-DWTSGV-Jbeta2.7 were also found in the clinically normal skin from the psoriasis patients, which might seem to be responsible for the artificial production of psoriatic lesions. The identified CDR3 motif was highly expressed in cutaneous lymphocyte antigen (CLA+) cells of peripheral blood mononuclear cells from psoriasis patients compared with the expression in healthy individuals. This result showed that the infiltrated CLA+ T cells with the Vbeta13-DWTSGV-Jbeta2.7 motif in peripheral blood mononuclear cells from psoriasis patients might be involved in the development of psoriatic lesions. In addition, the results in this study suggest that the infiltrated T cells with the Vbeta13-DWTSGV-Jbeta2.7 motif in psoriatic lesions may be involved in the pathogenesis of psoriasis.