Anitta Järvikallio

Several reports have shown the presence of T-helper lymphocytes with Th2 characteristics in the skin lesions of atopic dermatitis (AD). However. Th2 cells themselves require an exogenous pulse of IL-4 to initiate their differentiation and synthesis of IL-4. As mast cells have recently been shown to contain IL-4, this finding prompted us to investigate IL-4 in mast cells of AD lesions, to determine if they might provide the IL-4 pulse needed by the Th2 cells. In this study, we measured IL-4 immunoreactivity in mast cells of non-lesional and lesional skin sections from 20 patients with AD. Ten patients with nummular eczema (NE) without any atopic features or background, and five healthy subjects, served as the control groups. Mast cells were first identified using an enzyme-histochemical staining method for tryptase. Subsequently, the sections were photographed, the tryptase stain was removed, and IL-4 was demonstrated with a polyclonal antibody. The sections were photographed again, and the percentage of IL-4-positive mast cells was calculated. The percentage of mast cells exhibiting IL-4 immunoreactivity in the upper dermis in lesional vs, non-lesional skin was 66±18% vs. 37±18% in AD (P<0.0001, paired t-test), but only 46±19% vs. 31±22% in NE. In the skin of healthy controls, only 23±25% of the mast cells were positive for IL-4. In addition, a significant difference was found between lesional skin of AD vs. NE patients (P<0.008, unpaired t-test). Moreover, the staining intensity of IL-4 in mast cells was clearly increased in the lesional compared with the non-lesional AD skin. Mast cells appeared to be the main cell type containing IL-4 in 40% of the lesional AD skin specimens, whereas in the remaining 60% prominent IL-4-positive mononuclear cell infiltrates were also present. In the non-lesional skin, mast cells appeared to be the main cell type containing IL-4 in all specimens. These results indicate that mast cells are one major source of IL-4 in lesional and non-lesional AD skin, and they could contribute significantly to the development of AD.

Epidermolysis bullosa (EB), a group of heritable blistering diseases characterized by tissue separation within the cutaneous basement membrane zone, is inherited either in an autosomal dominant or autosomal recessive fashion. EB has been divided into four broad categories based on the precise level of tissue separation. In the dystrophic forms of EB (DEB), tissue separation occurs below the lamina densa within the upper papillary dermis at the level of anchoring fibrils, which are frequently altered in morphology, reduced in number, or entirely absent. Since type VII collagen is the major component of anchoring fibrils, the corresponding gene, COL7A1, was proposed as the candidate for DEB. Subsequent cloning of COL7A1 and elucidation of its genomic structure have led to identification of 53 distinct mutations in COL7A1 reported thus far. These mutations consist of nonsense mutations, small insertions or deletions resulting in frameshift and premature termination codons, splice site mutations, or missense mutations, particularly glycine substitutions within the collagenous domain of the protein. The types and combinations of these mutations and their positions along the type VII collagen molecule result in a spectrum of phenotypic severity and determine the mode of inheritance. Thus, examination of the mutation database has allowed genotype/phenotype predictions, with an impact on genetic counseling in this group of genodermatoses.

The distribution of mast cells (MCs) containing tryptase (T) and chymase (C) was studied in the non-lesional and lesional skin of 26 patients with atopic dermatitis (AD) and 23 patients with non-atopic nummular eczema (NE), and in the skin of eight healthy controls. T and C activities were demonstrated enzymehistochemically using Z-Gly-Pro-Arg-MNA and Suc-Val-Pro-Phe-MNA as substrates, respectively. The T- and C-containing MCs were counted separately in the epidermis, in contact with the basement membrane, in the papillary dermis and in different dermal levels (0.2 mm each). Also, the C protein was determined immunohistochemically. T-positive MCs were similarly distributed in non-lesional and lesional skin of both AD and NE. The MC number was relatively high in the upper dermis (papillary dermis and levels I and II) of non-lesional and lesional skin of AD. In the upper dermis of non-lesional AD and NE skin and in normal skin, about 50% of T-positive MCs displayed C activity, whereas the percentage in lesional AD and NE skin was only about 30%. In this respect, the non-lesional and lesional samples differed significantly from each other in both dermatoses (in AD p = 0.003; in NE p = 0.002, Students' t-test). In all samples the MC number decreased in the deeper dermal levels, although numerous T-containing MCs were still counted in the deeper dermis (dermal levels IV-VII) of lesional AD and NE skin, differing significantly from the MC number in normal skin (In AD p = 0.005, In NE p = 0.041). In the deeper dermis, the percentage of MCs containing active C was about 70% in non-lesional and lesional AD and NE, and about 90% in normal healthy skin. However, in the upper dermis of non-lesional and lesional skin of both AD and NE, about 80% of all MCs contained the C protein, which differed significantly from the value of 100% in normal skin (p < 0.05). In conclusion, the increased number of T-positive MCs in the upper dermis of non-lesional and lesional AD contributes to promoting inflammation. C apparently loses its activity in the upper dermis of lesional AD and especially in NE. Thus, the enzyme partially lacks its capability to suppress inflammation, such as degradation of neuropeptides and proteins. The dysregulation of these proteinases exists already in non-lesional skin of AD and NE.

To study the elements of neurogenic inflammation in psoriatic skin, morphological contacts were examined between mast cells and sensory nerves containing the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP) or vasoactive intestinal polypeptide (VIP). Because mast cells in psoriatic lesions appear in great numbers at the basement membrane (BM) zone, neuropeptide–mast cell contacts with the BM were also counted. A double stain for active mast cell tryptase and the neuropeptides was applied and the contacts were quantitated morphometrically. Sensory nerve–mast cell contacts were also studied three-dimensionally with a confocal laser scanning microscope. Increases in the contact values of SP and CGRP with mast cells, as well as with the BM, were obtained in developing (1–3 weeks) lesions when compared with their non-lesional controls. This increase reached statistical significance in mature lesions. In contrast, the corresponding contact values for VIP were decreased. By confocal microscopy, a close association between mast cells and sensory nerves was observed in the lesional dermis. Since tryptase is known to degrade CGRP but not SP, neurogenic stimuli, mainly via SP, can result in degranulation of mast cells, which release substances to enhance inflammation. At the BM zone in psoriatic lesions, the numerous mast cells loaded with tryptase can promote degradation of BM components and allow entry of various mediators to interact with keratinocytes.