Monocyte and neutrophil chemotaxis in psoriasis. Relation to the clinical status and the type of psoriasis

Exploring the association and causal effect between white blood cells and psoriasis using large-scale population data

Introduction

Psoriasis is a chronic inflammatory disease of the skin. A few studies have shown that psoriasis is an immune-mediated disease in which multiple immune cells play crucial roles. However, the association between circulating immune cells and psoriasis remains elusive.

Methods

To explore the role of circulating immune cells in psoriasis, 361,322 individuals from the UK Biobank (UKB) and 3,971 patients with psoriasis from China were included to investigate the association between white blood cells and psoriasis via an observational study. Genome-wide association studies (GWAS) and Mendelian randomization (MR) were used to evaluate the causal relationship between circulating leukocytes and psoriasis.

Results

The risk of psoriasis increased with high levels of monocytes, neutrophils, and eosinophils (relative risks and 95% confidence intervals, respectively: 1.430 (1.291-1.584) for monocytes, 1.527 (1.379-1.692) for neutrophils, and 1.417 (1.294-1.551) for eosinophils). Upon further MR analysis, eosinophils showed a definite causal relationship with psoriasis (odds ratio of inverse-variance weighted: 1.386, 95% confidence intervals: 1.092-1.759) and a positive correlation with the psoriasis area and severity index (PASI) score (P = 6.6 × 10^-5). The roles of the neutrophil-lymphocyte ratio (NLR), platelet-lymphocyte ratio (PLR), and lymphocyte-monocyte ratio (LMR) in psoriasis were also assessed. More than 20,000 genetic variations associated with NLR, PLR, and LMR were discovered in a GWAS analysis using the UKB data. Following adjustment for covariates in the observational study, NLR and PLR were shown to be risk factors for psoriasis, whereas LMR was a protective factor. MR results indicated that there was no causal relationship between these three indicators and psoriasis; however, NLR, PLR, and LMR correlated with the PASI score (NLR: rho = 0.244, P = 2.1 × 10^-21; PLR: rho = 0.113, P = 1.4 × 10^-5; LMR: rho = -0.242, P = 3.5×10^-21).

Discussion

Our findings revealed an important association between circulating leukocytes and psoriasis, which is instructive for the clinical practice of psoriasis treatment.

Increased Neutrophil Adherence in Psoriasis: Role of the Human Endothelial Cell Receptor Thy-1 (CD90)

The chronic inflammatory skin disease psoriasis is characterized by prominent skin infiltration by neutrophils and microabscess formation. The adhesion of leukocytes and subsequent transmigration through the activated endothelium is one prerequisite for the accumulation of these cells in skin. In recent studies, the human Thy-1 (CD90) was characterized as an adhesion molecule on activated endothelial cells (ECs) mediating the adhesion of neutrophils via the interaction with the beta2-integrin Mac-1. Based on these novel findings, we compared the roles of Thy-1 and ICAM-1 in the adhesion of neutrophils from patients with psoriasis to activated ECs. The adhesion of peripheral blood neutrophils of patients suffering from psoriasis to Thy-1-transfected cells as well as to activated, Thy-1-expressing human dermal microvascular ECs (HDMECs) is distinctly increased in comparison to the adhesion of neutrophils from healthy controls. In contrast, adherence of psoriatic neutrophils to ICAM-1 transfectants is, if at all, only slightly enhanced compared to healthy controls. The interaction of healthy as well as psoriatic polymorphonuclear cells to Thy-1 transfectants and HDMECs was significantly inhibited by blocking Thy-1 on ECs or its receptor Mac-1 on neutrophils, indicating the importance of this interaction for the adhesion of neutrophils to activated endothelium. In conclusion, our data indicate that the adhesion of neutrophils to activated ECs mediated by Thy-1/Mac-1 interaction is an important attachment mechanism facilitating their subsequent migration into lesional psoriatic skin.

[3H]PK11195 binding sites in human neutrophils: effect of fMLP stimulation and modulation in rheumatic diseases

OBJECTIVE

The objectives of this study were to evaluate the [3H]PK11195 binding parameters in a model of acute inflammation, the N-formylmethionine-leucine-phenylalanine (fMLP)-stimulated neutrophil cell membranes, and to analyze if alterations of peripheral-type benzodiazepine receptor (PBR) characteristics occurred in neutrophil cell membranes of patients affected by osteoarthritis (OA), rheumatoid arthritis (RA), and psoriasic arthritis (PA).

DESIGN AND METHODS

Neutrophils were obtained from 15 patients with OA, 15 patients with RA, and 15 patients with PA. fMLP stimulation was performed to aliquots of neutrophils from six healthy individuals. Evaluation of kinetic parameters of PBR was performed using [3H]PK11195, as specific radioligand compared with 15 healthy volunteers.

RESULTS

The results showed a significant decrease of Kd and Bmax in fMLP-stimulated neutrophil membranes. Moreover, an increase of PBR binding sites and affinity value was observed in neutrophils membranes from PA patients.

CONCLUSIONS

Our data suggested a fMLP modulation on [3H]PK11195 binding in human neutrophils. Moreover, our results showed an up-regulation of PBR in neutrophils of PA patients.

Anti-chemotactic activities of peptide-T: a possible mechanism of actions for its therapeutic effects on psoriasis

Peptide T is an octapeptide (ASTTTNYT) from the V2 region of gpl20 of HIV. D-[Ala]-Ser-Thr-Thr-Thr-Asn-Tyr-Thr-amide (DAPTA) is one of its analogue. DAPTA has been shown to resolve the psoriatic lesions. The mechanisms of action of peptide T for its therapeutic effect is not clearly understood. Lymphomononuclear cells play an important roles in inflammatory disease processes. Intraepidermal collection of lymphocytes is a unique feature of the inflammatory processes of psoriasis. It is believed that chemokine such as RANTES (C-C class) plays an important role for intraepidermal localization of the inflammatory infiltrates in psoriasis. In order to study the mechanisms, we have analyzed the effects of DAPTA on monocyte and lymphocyte chemotaxis. Chemotaxis of cells was measured by using Boyden chamber. DAPTA inhibited significantly the monocyte and lymphocyte chemotactic activity of RANTES (p < 0.005, < 0.001). Antichemotactic activities of peptide T analogue could be a possible explanation for its therapeutic efficacy in psoriasis.

Neutrophil functions and IL-8 in psoriatic arthritis and in cutaneous psoriasis

The aim of this study is to determine some functions of neutrophil in patients affected by psoriatic arthritis and to compare them to those of patients affected by cutaneous psoriasis and to normal controls. We used a model of experimental cutaneous inflammation allowing to separate a cluster of purified and viable PMN cells. Then we analyzed, within the three groups, the IL-8 concentration in serum and in the supernatant obtained from the inflammatory site to gather data on the possible pathogenic role played by this cytokine in psoriatic arthritis. We studied neutrophil functions in patients with cutaneous psoriasis and psoriatic arthritis, in acute phase, in comparison with healthy control subjects. We investigated in vivo neutrophil migration by Senn's skin window technique and measured adhesion assay and superoxide production in circulating and migrating neutrophils after different stimuli. We also measured IL-8 concentration in serum and in the supernatant obtained from the inflammatory site, artificially created through the skin window scrape. Neutrophil migration in vivo was significantly higher in both groups of patients than in controls. In the presence of fMLP, blood cells showed a burst of superoxide release, which was significantly more pronounced in patients when compared to healthy controls. Neutrophils from skin window scrape showed a much higher response to fMLP as compared to blood cells of all subject groups, but no differences were observed between patients and controls. No correlation was found between the three groups in adhesion ability under basal condition or in response to different stimuli by circulating and migrating neutrophils. Our results also show a great increase of IL-8 in the exudate from patients compared to controls. Our study shows that there is no difference in neutrophil functions between patients with psoriatic arthritis and cutaneous psoriasis; moreover we suggest that the source of high IL-8 levels are neutrophils rather than the keratinocytes.

SKALP/elafin gene polymorphisms are not associated with pustular forms of psoriasis

Psoriasis is a multifactorial skin disease characterised by epidermal abnormalities and infiltration by lymphocytes and polymorphonuclear leukocytes (PMN). Skin-derived antileukoproteinase (SKALP), also known as elafin, is a potent inhibitor of human leukocyte elastase and proteinase 3, two PMN-derived proteinases implicated in tissue destruction and leukocyte migration. We have shown that, at least at the protein level, SKALP is significantly decreased in lesional skin of patients with pustular psoriasis compared with plaque-type psoriasis. This finding raised the possibility that SKALP could be one of the candidate genes for pustular forms of psoriasis. We therefore performed single strand conformation polymorphism (SSCP) analysis on the SKALP gene to screen for mutations/polymorphisms in the exons of 30 patients with plaque-type psoriasis, 15 patients with pustular psoriasis and 48 healthy controls. In exon 1 a polymorphism was detected at position +43 relative to the translation start site, resulting in a substitution of threonine for alanine in the signal peptide. In the promoter region a dinucleotide repeat polymorphism was identified. Both polymorphisms were not associated with pustular psoriasis, or psoriasis in general. Our data indicate that the decrease in SKALP activity in pustular psoriasis is not caused by mutations in the coding region of the gene, and that there is no allelic association between pustular psoriasis and SKALP gene polymorphisms.

Laboratory findings and pathology of psoriatic arthritis

Over recent years there has been a great deal of interest in the immunology, molecular biology and pathology of psoriasis and PsA. The pathogenetic mechanisms in PsA are less well understood than those described for psoriasis. There are almost certainly genetic and immune components. What is not clear is whether there is a primary immune defect or whether unknown stimuli lead to the recruitment of the immune system and establishment of the disease; nor is it absolutely clear whether PsA is an extension of psoriasis in certain prone individuals. Vascular abnormalities are the earliest histopathological changes to occur in the psoriatic plaque and are also prominent in the psoriatic synovium. Espinoza et al (1982) have suggested there may be a primary vascular defect in PsA. The fact that vascular changes occur before infiltration of immunocompetent cells and are the first changes to resolve with treatment of psoriasis is likely to be significant. Abnormalities in the cellular kinetics and growth factor sensitivity of keratinocytes, fibroblasts and synoviocytes have been highlighted previously. The ability of these cells to produce growth factors and express HLA class II antigens demonstrates the potential for them to initiate and maintain inflammation. The development and possible increased incidence of PsA in patients with such profound immunodeficiency as acquired immune deficiency syndrome suggests that T helper cells do not play a significant role in the establishment of the disease (Arnett et al, 1991). Previously, many immune changes were described. Unfortunately they are non-specific and do not indicate a fundamental defect or marker of PsA. Vasey (1985) has suggested that insidious exposure to Gram-positive bacteria from the gut, tonsils and psoriatic plaques results in chronically stimulated monocytes, macrophages and dendritic cells. These cells are able to migrate throughout the body. Repeated microtrauma may result in the homing of these cells to sites of injury in the skin, synovium and tendons. Interaction with genetically hyperactive synoviocytes and keratinocytes with concomitant release of growth factors may precipitate early lesions of psoriasis and PsA. This hypothesis needs to be substantiated, but it ties together some of the varying observations seen. Many abnormal laboratory findings have been described. Unfortunately, none of the serological changes is sufficiently specific to be of great help in diagnosis. CRP levels and the ESR remain the best promise as markers of the inflammatory component of the arthritis, while other indicators correlate with certain facets of the disease pathology, but as yet have not found a true niche in the management of PsA.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of human monocyte functions by anthralin

Anthralin is a well-established and widely used compound for topical treatment of psoriasis. In recent years attention has been focused on the anti-inflammatory properties of anthralin, with particular reference to psoriasis. In this study the effect of anthralin on human monocyte chemotaxis, superoxide-anion generation, and enzyme degranulation, were investigated. For comparison, the effect of the clinically inactive anthralin derivative danthrone and the solvent (acetone) were also studied. The results show that anthralin potently inhibits stimulated human monocyte superoxide-anion generation and enzyme degranulation, with a half-maximal inhibitory concentration (IC50) of as low as 0.02 micrograms/ml. Chemotactic migration of monocytes, however, was only affected when very high doses of anthralin (10 micrograms/ml) were used for pretreatment of the cells. Danthrone, up to a concentration of 10 micrograms/ml, or acetone alone (0.1%, v/v), did not inhibit the monocyte functions tested. Our results indicate that anthralin at pharmacological concentrations is a potent and selective inhibitor of human monocyte pro-inflammatory activities, by inhibiting respiratory burst activity (e.g. superoxide-anion generation) and enzyme degranulation, without affecting chemotactic migration.

Treatment of psoriatic arthritis by extracorporeal photochemotherapy

Five patients with long-standing seronegative arthritis resistant to conventional therapy and who also had psoriasis of the skin were treated with photopheresis. This mode of treatment combines a lymphocyte-enrichment procedure with 8-methoxypsoralen-photochemotherapy. There was a marked in vitro effect on treated lymphocytes, with a reduction of viability, proliferation and mitogen response. There was a slight to moderate clinical improvement in four of the five patients with regard to the strength of grip, swelling, pain, morning stiffness, the dosage of non-steroidal anti-rheumatic drugs and the radiographical changes. The skin lesions did not respond to photopheresis. Short-term side-effects were minimal and consisted of a temporary sensitivity of the eyes to light and signs of circulatory dysregulation immediately after treatment. This experimental therapy has some measurable but not dramatic effect in improving psoriatic arthropathy.

Neutrophil function studies in clinical medicine

A complete evaluation of neutrophil function including: chemotaxis; adhesion; aggregation; phagocytosis; granule content and degranulation; respiratory burst activity; and bacterial killing; is expensive and requires the services of a specialized laboratory. However, preliminary screening of a patient with a predisposition toward infection, can be carried out using simple and inexpensive methods. These include examination of blood films, which may prove helpful in the diagnosis of Chediak-Higashi syndrome and specific granule deficiency; the Rebuck skin window test, which estimates chemotactic defects; the NBT test, which screens for chronic granulomatous disease patients; and peroxidase staining of the blood film in order to estimate the content of myeloperoxidase, when myeloperoxidase deficiency is suspected. For final diagnosis and determination of genetic transmission and radical treatment, ie, bone marrow transplantation, specific tests are indicated. Neutrophil function studies have also proved useful in detecting diseases in which defects in neutrophil function are secondary to the primary disorder. Indeed, increased neutrophil chemotaxis has been reported in the active phase of diseases such as: familial Mediterranean fever; psoriasis vulgaris, Behcet's syndrome and Sweet's syndrome. In these disorders the neutrophil chemotaxis assay has aided in the diagnosis and follow-up, particularly in evaluating the response to antiinflammatory agents, such as colchicine.

Methotrexate inhibits the human C5a-induced skin response in patients with psoriasis

In this study we examined the effects of intradermal injections of human complement split product C5a in 10 patients with psoriasis in long-term treatment with methotrexate (MTX). The C5a was injected at the end of the weekly MTX cycle just before the intake of the first MTX dose and 3 h after the second of the 3 doses. The C5a-induced skin response was evaluated by measuring the diameter of the wheal and the area of the flare and by erythema index (EI), which was determined objectively by reflectance spectrophotometry. In all patients the skin response was significantly depressed when C5a was injected after MTX intake. The decrease of wheal, flare, and EI averaged 61.6%, 71.1%, and 57.5%, respectively, when all parameters were obtained at maximal skin response. The in vitro chemotaxis of peripheral blood neutrophils and monocytes from the patients toward C5a was markedly inhibited after intake of MTX (p less than 0.01). The skin biopsies obtained after C5a injection before intake of MTX revealed a perivascular inflammatory infiltrate and considerable dermal edema. After MTX intake the number of infiltrating leukocytes and the degree of dermal edema was markedly reduced. This study indicates that MTX is a potent inhibitor of C5a-induced skin inflammation, and that this inhibition may be caused by a direct effect on circulating neutrophils and monocytes. The results obtained in this work support the idea that anti-inflammatory effects of MTX may be partially responsible for its antipsoriatic effect.

The enhanced monocyte and neutrophil chemotaxis in psoriasis is normalized after treatment with psoralens plus ultraviolet A and anthralin

The chemotactic activity of purified monocytes and neutrophils was studied in twenty-two psoriatic patients prior to the initiation of psoralens plus ultraviolet A (PUVA) or anthralin therapy and during the treatment. Patients with untreated, active psoriasis had increased chemotactic response of their monocytes and neutrophils to N-formyl-methionyl-leucyl-phenylalanine. Plasma from untreated psoriasis patients had an enhanced chemotactic activity toward neutrophils from persons without psoriasis. Treatment with PUVA or anthralin resulted in a progressive clearing of psoriatic lesions and in a significant depression of leukocyte chemotaxis 2 weeks after the start of the respective therapy. The chemotactic activity of both monocytes and neutrophils was normalized after 4 weeks of anthralin therapy and after 6 weeks of PUVA treatment. The chemotaxis-enhancing properties of plasma from psoriasis patients returned to normal values already after 2 weeks of treatment.