Alterations of clinically normal skin in early eruptive guttate psoriasis. A light- and electron-microscopic study

Mast cells and neutrophils release IL-17 through extracellular trap formation in psoriasis

IL-17 and IL-23 are known to be absolutely central to psoriasis pathogenesis because drugs targeting either cytokine are highly effective treatments for this disease. The efficacy of these drugs has been attributed to blocking the function of IL-17-producing T cells and their IL-23-induced expansion. However, we demonstrate that mast cells and neutrophils, not T cells, are the predominant cell types that contain IL-17 in human skin. IL-17(+) mast cells and neutrophils are found at higher densities than IL-17(+) T cells in psoriasis lesions and frequently release IL-17 in the process of forming specialized structures called extracellular traps. Furthermore, we find that IL-23 and IL-1β can induce mast cell extracellular trap formation and degranulation of human mast cells. Release of IL-17 from innate immune cells may be central to the pathogenesis of psoriasis, representing a fundamental mechanism by which the IL-23-IL-17 axis mediates host defense and autoimmunity.

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.

Behaviour of laminin 1 and type IV collagen in uninvolved psoriatic skin. Immunohistochemical study using confocal laser scanning microscopy

Previous studies have demonstrated the presence in psoriatic lesions of ultrastructural and molecular alterations of the basement membrane and an altered polarized distribution of the integrins; this latter alteration has also been observed in uninvolved skin. The aim of the present study was to determine, by means of immunolocalization with monoclonal antibodies directed against laminin 1 and type IV collagen and using confocal scanning laser microscopy, whether there are also alterations of the main components of the basement membrane in uninvolved skin. The findings showed a discontinuous and fragmented staining of laminin 1 and a normal distribution of type IV collagen. Taking into account both these results and the results of studies on epithelial cell lines, the authors hypothesize the existence of a functional deficit in psoriatic keratinocytes affecting the synthesis of the alpha 1 subunit of laminin. This deficit would explain: (1) the incapacity to produce mature trimeric laminin; (2) the altered assembly into a distinct basal lamina; (3) the loss of keratinocyte adhesion to the basement membrane; (4) alterations in the polarized distribution of the integrins; and (5) the consequent total or partial block of the cell signals regulating the processes of cytomorphosis. Already present in uninvolved skin, and enhanced by various irritative stimuli, this situation could be decisive for the appearance of psoriatic lesions.

Ultrastructural features of Langerhans cells in clinically uninvolved skin of psoriatics

Epidermal Langerhans cells (LC) from skin of clinically normal appearance in psoriatics were studied electron microscopically and compared with LC from the skin of healthy volunteers and from those with other dermatoses. Results show that LC from psoriatics display partly distinct cytoplasmic alterations. Moreover, about half of LC investigated were partly or mainly surrounded by clearly widened intercellular spaces, such that an immediate cellular contact with neighbouring keratinocytes was correspondingly decreased. Whether such LC are functionally altered remains to be clarified.

Significance and pathogenesis of basal keratinocyte herniations in psoriasis

Using transmission electron microscopy, we studied, quantitatively, basal keratinocyte herniations (BKH) in relation to the other basement membrane zone changes in psoriatic lesions of varying clinical activity, and in psoriasiform skin diseases. BKH appears to correlate with disease activity. They do not occur passively as a result of the formation of gaps in the basal lamina. BKH in active psoriasis are associated with electron-lucent areas suggestive of proteolytic enzyme release. Their apparent association with Langerhans cells, neutrophils, macrophages, and endothelial cells may point to these cells as the source of proteolytic enzymes in psoriasis. BKH may prove to be a useful marker for clinical psoriasis.

Mast cells and macrophages in early relapsing psoriasis

Five patients with widespread plaque-type psoriasis were treated continuously with clobetasol under occlusion. Clinical healing was seen after 6-10 days of treatment. All plaques treated in this way clinically relapsed approximately 12 days later. During the period of remission, sequential biopsies were taken and prepared for light and electron microscopy. Histologically, the earliest indications of relapse were endothelial alterations (swelling, intercellular widening) followed by the appearance of mast cells around the postcapillary venules; these mast cells showed signs of degranulation. Hours later, activated macrophages showing pericellular edema were present, and these migrated into the epidermis soon after. Associated with the presence of macrophages, there was a complete loss of desmosome-tonofilament complexes. Later, lymphocytes and neutrophils were seen. Under these experimental conditions, the psoriatic-tissue alterations appear to have been initiated by degranulating mast cells as well as by macrophages which later invaded the epidermis.

Mast cell degranulation in the evolution of acute eruptive guttate psoriasis vulgaris

Clinically normal psoriatic skin (CNPS) and psoriatic lesions (PLs) were studied for mast cell degranulation (MCD) in patients with acute eruptive guttate psoriasis vulgaris (AEGP) following penicillin-treated acute streptococcal throat infection. The clinically manifest duration of psoriasis at the time of the biopsies was 2, 5, 10, 14, or 21 days. Two types of MCD were distinguished. Type I was characteristic for those portions of the CNPS in which vascular and epidermal changes were detected, while the PLs showed both Type I and Type II MCD. In Type I MCD the extruded granules (MCGs) in the immediate vicinity of the mast cells appeared as intact bodies encased in a distinctly trilaminar membrane. Around subepidermal and subpapillary blood vessels, in stratum papillare without proximity of blood vessels, beneath the epidermal-dermal junction, in lamina lucida, and in intercellular space of strata basale and spinosum the MCGs appeared partly as intact structures and partly in more or less disintegrated form. In Type II MCD the MCGs were extruded without perigranular membranes. The data here presented showed that MCD is an early and constant feature in the evolution of AEGP.

Dermal and epidermal involvement in the evolution of acute eruptive guttate psoriasis vulgaris

A light and electron microscopic study of the evolution of acute eruptive guttate psoriasis vulgaris (AEGP) following penicillin-treated streptococcal throat infection is presented. The earliest recognizable changes, distinguished in clinically normal psoriatic skin (CNPS) from patients with psoriasis of 2 days' duration, comprised mast cell degranulation (Type I MCD), a vascular pattern showing endothelial cell gaps in postcapillary venules and postcapillary venules with endothelial cell hypertrophy and compressed lumen as well as epidermal involvement with punctiform spongiotic areas (PSAs). These early dermal and epidermal changes suggest that Type I MCD represents a primary morphologic event. Inflammatory infiltrate of mononuclear cells and exocytosis of mononuclear cells into the PSAs appeared when the concomitant overt psoriasis was 5-21 days old, and these changes were persistent in psoriatic lesions (PLs) of 2 days' duration. They are suggested to be precursors of overt psoriasis. In 2-day-old PLs, MCD (Types I and II) was a prominent feature. It was associated with (1) more extensive vascular changes, (2) inflammatory infiltrate of mononuclear cells and scanty polymorphonuclear leukocytes, (3) epidermal hyperplasia, and (4) migration of a few polymorphonuclear leukocytes through the epidermis with formation of Munro microabscesses in parakeratotic areas of stratum corneum. From the morphologic viewpoint, the progression from 2-day-old to fully evolved PLs seemed basically to be quantitative. The demonstration of MCD as a salient feature in the evolution of AEGP may have future therapeutic and preventive implications for psoriasis.

Low strength anthralin in psoriasis

Anthralin in low concentrations (0.01%--0.03%) was applied in an ointment form once per day in the hospital to 130 psoriasis patients. The treatment program included also the use of UVB light, emollients and bath oil and an antihistamine. Clearing of psoriasis was achieved in all patients in an average time of 4 weeks. The involution of the lesions was carefully studied by correlated clinical observations, light microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Striking healing of the holes in the stratum corneum and of the gaps in the basement membrane occurred. Low strength anthralin, in addition to its effectiveness, did not produce irritation, staining or side-effects.

Target role of Langerhans cells in mycosis fungoides: transmission and immuno-electron microscopic studies

Langerhans cells of the epidermis are "special" macrophages, as indicated by their expression of Fc and C3 receptors and Ia antigen. Functionally, they can replace macrophages in presentation of antigens to T cells and in the MLR. Ultrastructural and immunologic studies were carried out on epidermal samples of mycosis fungoides. As in contact allergy, apposition of lymphocytes to Langerhans cells was noted. Destruction of Langerhans cells appeared to act as the focus for the development of Pautrier microabscesses. This destruction was accompanied by ingress of histocytic cells, probably related to the stem cell population for Langerhans cells. The target cell role of Langerhans cells appears to be similar in contact allergy and mycosis fungoides.