Is chronic plaque psoriasis triggered by microbiota in the skin?

There is a known association between psoriasis and Crohn disease (CD). Patients with CD are five times more likely to develop psoriasis, and, conversely, patients with psoriasis are more likely to develop CD. Many gastroenterologists now accept that CD results from a breakdown of immune tolerance to the microbiota of the intestine in genetically susceptible individuals. The microbiota of the skin have recently been investigated in psoriasis. Firmicutes was the most common phylum, and Streptococcus the most common genus identified. Beta-haemolytic streptococci have been implicated in both guttate and chronic plaque psoriasis. Furthermore, the innate immune system has been shown to be activated in psoriasis, and many of the genes associated with the disease are concerned with the signalling pathways of the innate immune system, notably interleukin-23 and nuclear factor κB. Patients with psoriasis also have an increased incidence of periodontitis, a disease thought to be due to an abnormal response to normal oral commensals. Based on the similarities between CD and psoriasis, we propose that psoriasis is due to a breakdown of immune tolerance to the microbiota of the skin. In support of this hypothesis we provide evidence for microbiota in the skin, activation of the innate immune system, and genetic abnormalities involving the innate immune system.

Concepts in psoriasis: psoriasis and the extracellular matrix.

Post-streptococcal guttate psoriasis only sometimes progresses to the persistent plaque psoriasis. We have previously proposed that psoriasis is driven by multiple extradomain A+ fibronectin (EDA+ FN) 'feedback loops'. The psoriasis-specific loop, the 'keratinocyte loop', depends upon expression by keratinocytes of α5ß1 integrin. In normal skin, α5ß1 expression is minimal or absent in resting epithelial cells, where basal cells are anchored to the laminin component of the basement membrane (via integrins α6ß4 and α3ß1). However, when the laminin layer is disrupted, due to wounding for instance, α5ß1 is then strongly expressed by basal cells as a means for anchoring. At uninvolved skin sites in patients with psoriasis the laminin layer within the basement membrane is disrupted, with a consequential increase in the expression by basal keratinocytes of EDA+ FN and α5ß1. We are postulating that in guttate psoriasis streptococcal lytic enzymes, and in particular streptokinase, may - via plasminogen activation - initiate a disruption of the laminin layer in the basement membrane. It is also possible that the expression by proliferating keratinocytes of plasminogen-activating factor might result in additional laminin digestion. The suggestion is that progression of guttate psoriasis to full-blown plaque psoriasis, or to its spontaneous resolution, is governed largely by the triggering of humoral immune responses. Thus, if streptococcal lytic enzymes are neutralized by host antibodies in advance of irreversible and lasting damage to the basement membrane of the dermal papillae, then guttate psoriasis will resolve spontaneously. In contrast, if permanent damage is induced prior to effective neutralization of the relevant bacterial toxins, then keratinocytes will become chronically destabilized. The consequence will be to liberate keratinocytes to proliferate in response to various stimuli, and to continue to elaborate plasminogen activation enzymes; the combined effect being, in concert with immunological priming, to precipitate and sustain plaque psoriasis.

Psoriasis and extra domain A fibronectin loops.

We have previously postulated that as well as T-helper (Th) 1 and Th17 cells, the transforming growth factor (TGF)-beta/fibronectin (FN)/alpha5beta1 pathway is central to psoriasis pathogenesis. EDA+ FN refers to an alternatively spliced isoform of FN with an additional domain known as extra domain A. EDA+ FN has two important properties pertinent to psoriasis lesions: it stimulates keratinocyte hyperproliferation, and, through stimulation of Toll-like receptor (TLR) 4, stimulates production of proinflammatory cytokines. EDA+ FN production induced by TGF-beta stimulation can be maintained in psoriasis lesions via two main feedback loops. Firstly, EDA+ FN stimulates proliferation of keratinocytes, which, in an autocrine fashion, will release more EDA+ FN. Secondly, EDA+ FN stimulates TLR4 expressed by antigen-presenting cells resulting in the production of proinflammatory cytokines such as tumour necrosis factor-alpha, interleukin (IL)-1, IL-6 and IL-12. The resultant promotion of cutaneous inflammation results in the recruitment of Th1 cells, which also produce EDA+ FN. We propose that these 'FN loops' contribute to the maintenance and progression of psoriatic lesions. Finally, although the association between psoriasis and heart/thrombotic disease remains unclear one plausible link may be the promotion of atherosclerosis and thrombotic heart disease by EDA+ FN.

Psoriasis and streptococci: the natural selection of psoriasis revisited.

We have previously postulated that surviving invasive streptococcal infections may have been a factor in psoriasis becoming a common skin disease in some parts of the world. Many of the candidate genes linked to psoriasis are associated with the acquired or innate immune system, which are also important in host defence to invasive streptococcal infections. High rates of positive streptococcal throat swabs among patients with chronic plaque psoriasis suggest that they are efficient at internalizing/carrying beta-haemolytic streptococci. Internalization of streptococci in the throat is dependent upon the transforming growth factor (TGF)-beta/fibronectin/alpha 5 beta 1 integrin pathway. The immune cell Th17 and its related cytokine network are important in mucosal defence, being very effective against extracellular microbes but having little effect on intracellular organisms. The TGF-beta/fibronectin/alpha 5 beta 1 integrin pathway and the Th17 cell network also appear to be operative in psoriasis, animal models of both TGF-beta and alpha 5 beta 1 cutaneous overexpression being associated with characteristic psoriasis lesions. We postulate that some of the genotypic/phenotypic changes in different immunological pathways in psoriasis, including the acquired T-cell response, the innate immune response, the TGF-beta/fibronectin/alpha 5 beta 1 integrin pathway and the Th17 cell system, confer protection against mortality during epidemics of invasive streptococcal infections, heightened efficiency in internalizing and allowing carriage of streptococci as well as predisposition to the development of psoriasis.

HLA Cw*06 is not essential for streptococcal-induced psoriasis.

BACKGROUND: Streptococcal throat infections and HLA Cw6 (Cw*06) have been implicated in the pathogenesis of psoriasis, particularly in the guttate form. OBJECTIVES: To study 105 Irish patients with psoriasis to investigate the relationship between streptococcal infections and Cw*06. METHODS: The patients were divided into two groups: those with guttate psoriasis or guttate flare (guttate group, GG, n=64) and those with chronic plaque psoriasis (chronic plaque group, CPG, n=41). RESULTS: The incidence of Cw*06 was 86% in the GG and 73% in the CPG, which was not significantly different (P=0.1725) but the incidence in both groups was significantly higher than in an Irish control group (18%) (P<0.0001 vs. GG and P<0.0001 vs. CPG). Evidence for streptococcal infection was higher in the GG (56%) than in the CPG (32%) (P=0.0231). Of those patients with evidence of streptococcal infection, 30 of 36 GG (83%) and nine of 13 CPG (69%) patients possessed the Cw*06 genotype. CONCLUSIONS: Thus, not all patients with streptococcal-related psoriasis carry Cw*06. The role of Cw*06 in psoriasis, if any, has yet to be determined.

Normal keratinocytes express Toll-like receptors (TLRs) 1, 2 and 5: modulation of TLR expression in chronic plaque psoriasis.

BACKGROUND: Toll-like receptors (TLRs) are part of the innate immune system involved in the response to microbial pathogens. TLR2 recognizes various ligands expressed by Gram-positive bacteria, while TLR3, TLR4 and TLR5 are specific for double-stranded RNA, Gram-negative lipopolysaccharides and bacterial flagellin, respectively. OBJECTIVES: To determine, firstly, whether epidermal keratinocytes of normal skin express TLRs and, secondly, whether modulation of TLR expression occurs in psoriasis, an inflammatory skin disease associated with certain microorganisms such as streptococci, staphylococci and yeasts. METHODS: Eight samples of normal, and 15 samples of lesional and nonlesional psoriatic skin were stained with polyclonal antibodies specific for TLR1-5 using an avidin-biotin-peroxidase technique. RESULTS: Epidermal keratinocytes in normal skin constitutively expressed TLR1, TLR2 and TLR5, while TLR3 and TLR4 were, in most cases, barely detectable. Cytoplasmic TLR1 and TLR2 were expressed throughout the epidermis, with higher staining of the latter on basal keratinocytes, while TLR5 expression was concentrated in the basal layer. In contrast, in lesional epidermis from patients with psoriasis, TLR2 was more highly expressed on the keratinocytes of the upper epidermis than on the basal layer, while TLR5 was downregulated in basal keratinocytes compared with corresponding nonlesional psoriatic epidermis. In addition, nuclear TLR1 staining was observed in the upper layers of both nonlesional and lesional psoriatic epidermis, but not in that of normal skin. CONCLUSIONS: These findings suggest that TLRs expressed by epidermal keratinocytes constitute part of the innate immune system of the skin. The relevance of altered keratinocyte TLR expression in psoriasis remains to be determined.

Epidermal CD8+ T cells reactive with group A streptococcal antigens in chronic plaque psoriasis.

Chronic plaque psoriasis is a T cell mediated disease associated with group A streptococci (GAS). We have previously shown the presence of a psoriasis-specific dermal Th1 subset that recognizes GAS antigens. To assess whether GAS-reactive T cells are also present in lesional epidermis, fresh cell suspensions or T cell lines isolated from lesional epidermis of 33 psoriasis patients were stained for intracellular interferon-gamma after stimulation with GAS antigens. The patients were typed by PCR for HLA-DR7 and HLA-Cw6 expression. A subset of GAS-reactive CD8+ T cells (2.4% +/- 2.4) was found in 14/21 (67%) fresh cell suspensions. A smaller subset of GAS-reactive CD4+ T cells (0.9% +/- 0.9) was found in 13/21 (62%) fresh cell suspensions, which was expanded in the T cell lines. There was a significant inverse correlation between the proportions of GAS-reactive CD4+ and CD8+ T cells in the fresh suspensions (r = -0.48, P = 0.0277). The presence of GAS-reactive CD4+ or CD8+ T cells did not correlate with HLA-DR7 or HLA-Cw6 expression, respectively. This study has demonstrated GAS-reactive CD8+, and to a lesser extent CD4+, T cell subsets in psoriatic epidermis and provides further evidence that GAS antigens may play a role in the pathogenesis of chronic plaque psoriasis.

Non-M protein(s) on the cell wall and membrane of group A streptococci induce(s) IFN-gamma production by dermal CD4+ T cells in psoriasis.

Recently we have demonstrated that a disease-specific subpopulation of CD4+ T cells isolated from skin lesions of chronic plaque psoriasis produces interferon-gamma in response to group A streptococcal (GAS) antigens. To determine if these T cells recognize M or non-M protein, extracts from cell wall of type M6 GAS (M6W) and its isogenic M gene deletion mutant (M-W), M6 membrane extract (M6M) and recombinant M6 protein (rM6) were used to stimulate GAS-reactive T-cell lines from nine patients with chronic plaque psoriasis. T-cell lines were incubated with or without streptococcal extracts for 18 h in the presence of a transport inhibitor, stained for surface CD4 and intracellular cytokine expression, and analysed by flow cytometry. Variable numbers (0.2-34%) of CD4+ T cells produced interferon-gamma, in all but one of the T-cell lines tested, in response to M6W, M-W and M6M extracts. No significant difference between the response to M6W and M-W extracts was detected. In addition, rM6 protein failed to increase CD4+/interferon-gamma+ T-cell numbers in seven of nine T-cell lines compared to medium alone. For the group, there was a highly significant correlation between the responses to the three extracts (M6W vs M-W, P = 0.0005; M6W vs M6M, P = 0.0003; M-W vs M6M, P = 0.0001). Low or minimal numbers of interleukin-4- and interleukin-10-producing CD4+ T cells were occasionally induced. These findings suggest that a subpopulation of CD4+ T cells isolated from skin lesions of chronic plaque psoriasis patients produces interferon-gamma in response to non-M protein(s) present on the cell wall and membrane of GAS.

Epidermal CD8+ T cells in chronic plaque psoriasis are Tc1 cells producing heterogeneous levels of interferon-gamma.

The majority of epidermal CD8+ T cells in chronic plaque psoriasis are activated Tc1 cells producing interferon-gamma and no interleukin-4, a small proportion of which express NK-T receptors. To quantitate their level of cytokine production and characterize them further, CD8+ T cells were isolated from epidermal cell suspensions of lesional biopsies from 24 patients with chronic plaque psoriasis. T-cell lines (TCL) were established by culture of CD8+ T cells with feeders and IL-2 for 11 days and expansion with PHA. Ten TCL were stained for surface markers; 6 were cloned with PHA by limiting dilution. Interferon-gamma, interleukin-4 and interleukin-10 production was measured by ELISA after PMA/anti-CD3 activation of 15 TCL and 39 CD8+ T-cell clones. The 10 TCL stained were CD8alphabeta+ (93.3%), T-cell receptor-alphabeta+ (99.5%), costimulatory molecule CD28+ (90.1%), with a small CD8alphaalpha+ population (2.3%). No NK-T-cell receptor CD158a or CD158b expression was detected, whilst CD94 was expressed on 6.2% of cells in 6/9 TCL. All the TCL and 37/39 CD8+ T-cell clones produced interferon-gamma but no or minimal interleukin-4 or interleukin-10. The TCL produced a wide range of interferon-gamma levels (138 to 15,020 pg/ml). Clones from 3 patients showed low levels (60 to 1,410 pg/ml), from 2 patients high levels (6,105 to 43,040 pg/ml) and from 1 patient a wide range (405 to 36,010 pg/ml) of interferon-gamma production. Thus epidermal CD8+ Tc1 cells in chronic plaque psoriasis produce highly heterogeneous levels of interferon-gamma, which may reflect clinical diversity.

Change of treatment from cyclosporin to mycophenolate mofetil in severe psoriasis.

Eight patients whose severe psoriasis was treated with long-term cyclosporin (range 2-11 years; mean 7.6 years) were changed to mycophenolate mofetil (MMF), because of nephrotoxicity in seven and hypertension and lack of efficacy in one. In five patients psoriasis control significantly deteriorated and in three patients disease control deteriorated slightly in periods ranging from 2 to 32 weeks. Renal function improved in all six patients with cyclosporin-induced nephrotoxicity treated with MMF for more than 2 weeks. From this data it would appear that MMF is not as effective as cyclosporin in controlling severe psoriasis. However, MMF did offer reasonable disease control in three of eight patients and allowed renal function to improve, and so may have a place in the treatment of some patients unable to take cyclosporin because of renal toxicity.

Skin CD4+ T cells produce interferon-gamma in vitro in response to streptococcal antigens in chronic plaque psoriasis.

Recently, we have demonstrated that group A streptococcal antigen reactive T cells are present in the skin lesions of chronic plaque psoriasis. To determine the cytokine profile (interferon-gamma, interleukin-4 and interleukin-10) of these T cells in response to streptococcal antigens, T cell lines were cultured from untreated lesional skin of 13 patients with chronic plaque psoriasis and 12 patients with other inflammatory skin diseases. T cell lines were incubated with or without a sonicated heat-killed mixture of group A streptococcal isolates for 18 h in the presence of a transport inhibitor, stained for surface CD4 or CD8 and intracellular cytokine expression, and analyzed by flow cytometry. Psoriatic T cell lines were grown from 10 of 13 patients and were predominately CD4+ (64%-85%) with 10%-32% CD8+ T cells. Variable numbers of CD4+ T cells produced interferon-gamma (0.8%-35%, median 13.9) in eight of 10 T cell lines (p < 0.02). In contrast, CD4+ T cells in five of 12 T cell lines obtained from disease controls did not produce or produced minimal interferon-gamma in response to group A streptococcal isolates; this was significantly different from the psoriatic T cell lines (p < 0.05). Small numbers of interleukin-10 positive (0.8%-1.3%) and interleukin-4 positive (2.1%-2.5%) CD4+ T cells induced by group A streptococcal isolates were also present in two out of five and three out of five psoriatic T cell lines, respectively. This was significantly less in each case than the numbers of CD4+/interferon-gamma+ T cells (p < 0.05). Cytokine-positive CD8+ T cells were rarely observed. These findings demonstrate that a subpopulation of CD4+ T cells in chronic plaque psoriasis skin lesions produces interferon-gamma in response to streptococcal antigens and may be relevant to the pathogenesis of psoriasis.

Haematological disease in siblings with Rothmund-Thomson syndrome.

We report two siblings with Rothmund-Thomson syndrome (RTS); the older sister died of acute myeloblastic leukaemia and the younger sister has a slowly progressive leucopenia. Her prognosis is guarded in view of the increased incidence of neoplasms in this condition. More than 200 cases of RTS have now been reported worldwide.1 This is the first report of siblings with haematological disease and RTS.

Unusual giant comedo naevus.

Comedo naevi are usually well circumscribed, and although extensive cases have been reported individual lesions crossing the midline are rare. Associated neurological, skeletal and ophthalmological abnormalities are also recognized. thus, the patient now reported is unusual in that she had an extensive systematized comedo naevus with crossing of the midline but no associated abnormalities. Topical tretinoin was helpful in improving the texture and appearance of the comedones, and various larger lesions responded to curettage.

Renal function after 10 years' treatment with cyclosporin for psoriasis.

Renal function was assessed by measuring serum creatinine and glomerular filtration rate (GFR) in two groups of patients with chronic plaque psoriasis who had been treated with cyclosporin A (CyA), average dose 2.8 mg/kg per day (range 1-5 mg/kg per day). Group I was our original cohort of nine patients, seven of whom had received CyA for an average period of 10 years (range 9.5-11 years). These seven patients showed a persistent increase in serum creatinine > 30% from baseline measurement and four of the seven had persistent increases > 50%. The GFR, which was first measured after 2.5 years of treatment, showed at 10 years a decrease of > 30% in two patients and of > 50% in one patient. Three of the seven showed stable renal function while two had repeat renal biopsy because of deteriorating renal function and histology showed further evidence of CyA nephrotoxicity compared with that after 5 years' treatment. Two of the nine patients in group I had discontinued CyA 5 years previously after 5 years of treatment because of CyA nephrotoxicity on renal biopsy and impaired renal function. This impairment of renal function showed improvement during the 5 years of follow-up, implying reversibility of CyA nephrotoxicity. The second group of 20 patients had received CyA for an average duration of 6 years (range 5-8 years). Nine of the 20 patients showed persistent increases in serum creatinine of > 30% from baseline and five showed persistent increases of > 50%. The GFR showed a persistent decrease of > 30% in seven patients and of > 50% in two patients. This study has shown that nephrotoxicity is associated with long-term treatment with CyA. However, there is patient variation as to when nephrotoxicity commences and its speed of progression. On discontinuing CyA the impairment of renal function improves with time. Providing renal function is monitored with GFR and renal biopsy in addition to serum creatinine then long-term (5-10 years) CyA treatment can be justified in severe psoriasis not responsive to other treatments.

Cytokine expression in psoriatic skin lesions during PUVA therapy.

To determine whether an improvement in skin lesions as a result of PUVA therapy may be correlated with changes in cytokine patterns, RT-PCR amplification was used to compare the levels of IL-2, IL-6, IL-8, IL-10, TNF-alpha and IFN-gamma cytokine mRNA expression in serial biopsies from three chronic plaque psoriatic patients. In each case, 3-mm punch biopsies were taken from lesional skin before and during 2-28 days of treatment with PUVA. Total mRNA was extracted from each biopsy, cDNA synthesized, and then amplified by 35 cycles of PCR using cytokine-specific primers. The specificity of the PCR products was confirmed by the Southern blot technique. Substantial levels of specific mRNA for each of the cytokines studied was present in the lesions prior to treatment. In two of the three patients who responded well to PUVA, a reduction in all the cytokines including IL-10 was observed compared with baseline levels. In contrast, PUVA proved to be ineffective in clearing the psoriasis of the third patient whose skin lesions worsened during the course of treatment. This was accompanied by an increase in IFN-gamma but not of the other cytokines investigated, above the pretreatment level. This study showed an association between PUVA-induced resolution and decreases in the levels of various cytokines highly expressed in psoriatic lesions.

A comparison of the stimulatory effects of cytokines on normal and psoriatic keratinocytes in vitro.

Keratinocytes from normal and psoriatic skin were tested for their in vitro proliferative response to a range of concentrations of rIL-6, rTGF alpha, rIL-8 and rGM-CSF using a serum-free culture system. With one exception, all normal cultures (11/12) were stimulated by 1000 ng/ml IL-6 (P < 0.001). Six out of ten psoriatic keratinocyte cultures were also stimulated at this concentration, but this just failed to reach significance (P = 0.05). As a group, the response by psoriatic keratinocytes to IL-6 was significantly less than that of normal keratinocytes (P = 0.02). TGF alpha at 1 ng/ml induced proliferation in approximately 60% of both normal (8/12, P < 0.05) and psoriatic (6/10, P < 0.01) keratinocyte cultures; there was no significant difference between the responses of the two groups to this cytokine. In addition, small numbers of both normal and psoriatic cultures responded to TGF alpha over a concentration range of 0.1 to 100 ng/ml. Approximately half of the normal and psoriatic cultures were stimulated by 10-1000 ng/ml IL-8. However, the effect was not significant for the group at any of the concentrations tested. GM-CSF had minimal to no effect on most of the normal and psoriatic cultures tested. This study showed that psoriatic keratinocytes are equally responsive to the stimulatory effects of TGF alpha and IL-8, but are less susceptible to IL-6 compared to keratinocytes from normal skin. These findings are consistent with a role for these cytokines in the maintenance of a hyperproliferative epidermis in psoriasis.

Decreased T cell reactivity to trypsinized group A, type M22 streptococci in psoriasis.

The proliferative responses of peripheral blood mononuclear cells from patients with guttate and chronic plaque psoriasis to streptococcal M protein were investigated using whole and trypsinized group A M22-positive streptococci. Peripheral blood mononuclear cell responses to whole type M22 group A streptococci were significantly increased in guttate, but not chronic plaque, psoriasis patients compared to 17 non-psoriatic controls (p < 0.05; n = 17). A significant reduction of this response was observed in both guttate (p < 0.001; n = 17) and chronic plaque (p < 0.01; n = 27) psoriatic patients, but not in the control group, after repeated trypsinization to remove M protein from the streptococci. Furthermore, the difference between the peripheral blood mononuclear cell response to untrypsinized and trypsinized streptococci was significantly greater in the guttate patients than in the controls (p < 0.02). This preliminary study has shown an increased reactivity of T lymphocytes with specificity for trypsin-sensitive protein expressed by type M22 streptococci in the peripheral blood of patients with psoriasis.

Restricted T-cell receptor V beta gene usage in the skin of patients with guttate and chronic plaque psoriasis.

A strong association between acute guttate psoriasis and group A, beta-haemolytic streptococcal infections is well established. Furthermore, streptococcal M proteins and toxins have been shown to act as superantigens, stimulating subpopulations of T lymphocytes expressing particular V beta families. We have therefore studied the possible role of streptococcal superantigens in psoriasis by staining peripheral T lymphocytes and skin sections from patients with guttate or chronic plaque psoriasis for the expression of nine TCR V beta families, using a range of monoclonal antibodies. A marked over-representation of V beta 2+ T lymphocytes was observed in the dermis and epidermis of patients in both groups, when compared with T lymphocytes in their peripheral blood. A less marked dermal increase in V beta 5.1+ T lymphocytes was also observed in these patients. These findings are consistent with the involvement of a superantigen, possibly streptococcal, in the pathogenesis of psoriasis.