A diadectid skin impression and its implications for the evolutionary origin of epidermal scales.

Corneous skin appendages are not only common and diverse in crown-group amniotes but also present in some modern amphibians. This raises the still unresolved question of whether the ability to form corneous skin appendages is an apomorphy of a common ancestor of amphibians and amniotes or evolved independently in both groups. So far, there is no palaeontological contribution to the issue owing to the lack of keratin soft tissue preservation in Palaeozoic anamniotes. New data are provided by a recently discovered ichnofossil specimen from the early Permian of Poland that shows monospecific tetrapod footprints associated with a partial scaly body impression. The traces can be unambiguously attributed to diadectids and are interpreted as the globally first evidence of horned scales in tetrapods close to the origin of amniotes. Taking hitherto little-noticed scaly skin impressions of lepospondyl stem amniotes from the early Permian of Germany into account, the possibility has to be considered that the evolutionary origin of epidermal scales deeply roots among anamniotes.

Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur.

Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales. Here we show that this resemblance is more than skin deep. We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius. Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers. These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy. Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment. Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation. Convergence of ichthyosaurs with extant marine amniotes thus extends to the ultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life.

Hydradermabrasion through the lens of Line-Field Confocal Optical Coherence Tomography.

BACKGROUND: Hydradermabrasion, also known as "HydraFacial," is an exfoliative cosmetic procedure for skin rejuvenation that has gained popularity. Despite its increasing popularity, clinical studies validating its efficacy with non-invasive assessment of histological changes to the skin, are scarce. In this study, we used Line-Field Confocal Optical Coherence Tomography (LC-OCT), an optical imaging device, to non-invasively visualize microscopic changes to skin anatomy after hydradermabrasion treatment. MATERIALS/METHODS: Eight volunteers (Fitzpatrick skin types II-V) were recruited for this study. Images, using LC-OCT (DeepLive, DAMAE medical) were obtained before and after hydradermabrasion and at 2 weeks post-treatment. A commercially available hydradermabrasion device was utilized to perform the dermabrasion. RESULTS: In the epidermis, initially, a decrease in the average thickness of the stratum corneum, from 9.42 to 6.67 µm was visualized in LC-OCT images after hydradermabrasion. However, at 2 weeks of follow-up, the average stratum corneum thickness was 9.75 µm, resulting in an overall increase in the average thickness after treatment. Improved homogenization of the stratum corneum and decreased number of undulations in the epidermis post-treatment were also visualized. In all the subjects, the superficial dermis appeared stretched, which returned to baseline by the 2-week follow-up. At the 2-week follow-up, there were no visible differences in the quality and quantity of collagen fibers in the dermis. CONCLUSION: In our study, LC-OCT images of the epidermis and dermis demonstrated microscopic features of skin rejuvenation when treated with hydradermabrasion. Thus, not only highlighting the efficacy of hydradermabrasion but also the potential of LC-OCT to serve as a tool for visualizing the microscopic effects of cosmetic procedures on skin anatomy.

Structural and functional differences in skin of colour.

The term 'skin of colour' (SOC), refers to individuals of African, Latinx, Asian, Native Hawaiian, Pacific Islander and Indigenous descent. These individuals typically have darker skin tones compared with white individuals and they often present with unique disorders of the skin or with common disorders that have a unique appearance. Certain skin conditions commonly associated with SOC patients, in contrast to individuals with lighter skin tones, are explained by structural and functional differences between this population and the white population. Variations in functional differences between these two groups are dependent on structural differences in melanosomes, stratum corneum, epidermis and dermis. Understanding the structural distinctions between white populations and SOC populations will provide insight into common disorders in SOC patients, including hyperpigmentation, hypopigmentation, dry skin, scaliness, xerosis, sensitive skin and keloids. Furthermore, understanding structural and functional skin difference will encourage more research regarding aetiology of disease and therapeutic interventions.

Establishment and characterization of proliferating primary cultures of equine epidermal keratinocytes.

Skin-derived tissue cultures are a useful model to study molecular mechanisms of skin renewal and pathogenesis of dermal diseases. Horses often suffer from skin diseases, skin trauma and problems with proper wound healing, which could be improved by in vitro grown keratinocyte grafts. Herein we describe establishment and characterization of equine skin-derived primary cell cultures, using enzymatic and explant methods. The established cell lines of primary equine keratinocytes (peK) maintained high proliferative capacity for over five passages and expressed different epithelial/keratinocyte-specific markers. Characterization of the primary culture was performed in parallel with localization studies of the markers in the skin histological sections, using commercially available antibodies. Relative expression of typical differentiation stage-specific markers was determined in the established cell lines, using RT-qPCR. Basal (proliferating) keratinocytes were the predominant cell type in the established cell lines, but low expression of post-mitotic keratinocyte markers was also detected. Differences in marker expression were observed neither between the peK originating from two different animals nor between the peK established with two different methods (enzymatically or by explanting). The described methods in combination with the suggested characterization and differentiation markers are suitable for establishment of proliferating peK and evaluation of their differentiation status.

Adhesive pads of gecko and anoline lizards utilize corneous and cytoskeletal proteins for setae development and renewal.

The formation of the complex pattern of setae in adhesive pads of geckos and anoline lizards has been analyzed by ultrastructural, autoradiographic, and immunohistochemical methods. Setae terminate with spatulated ends responsible for adhesion that allow these lizards to climb vertical substrates and conquer arboreal niches. Setae derive from a complex interfaced molding between two specialized epidermal layers of the shedding complex that determines the cyclical skin molting, Oberhautchen and clear layers. Setae result from the action of setae cytoskeleton and the surrounding cytoplasm of clear cells. An intense protein synthesis, indicated by histidine and proline autoradiography, takes place during setae formation. Corneous and cytoskeletal proteins such as beta-proteins (CBPs), intermediate filament keratins (IFKs), actin, RhoV, tubulin, plakophilin-1, are produced during setae formation. Microfilaments of actin and microtubules of tubulin grow inside the elongating setae. Microtubules associated with filaments of unknown IKFs are produced in the cytoplasm of clear cells, forming a helical cytoskeleton that surrounds the growing setae. Oberhautchen and clear cells are tightly joined by numerous desmosomes and plakophilin-1 is mainly localized along the perimeter of these cells. These observations suggest that actin and tubulin are present in a dynamic form in the forming setae and in the surrounding cytoplasm of clear cells. Aside the localized micro-deformations of the cell membranes leading to setae formation the cytoskeleton determines the accumulation of CBPs inside the growing setae and the spatula. How the genome determines the specific pattern of cytoskeletal organization with the resulting species-specific setae branching remains unknown.

In vivo Tracking of DNA for Precise Determination of the Stratum Corneum Thickness and Superficial Microbiome Using Confocal Raman Microscopy.

The skin barrier function is mostly provided by the stratum corneum (SC), the uppermost layer of the epidermis. To noninvasively analyze the physiological properties of the skin barrier functionin vivo, it is important to determine the SC thickness. Confocal Raman microscopy (CRM) is widely used for this task. In the present in vivo study, a new method based on the determination of the DNA concentration profile using CRM is introduced for determining the SC thickness. The obtained SC thickness values are compared with those obtained using other CRM-based methods determining the water and lipid depth profiles. The obtained results show almost no significant differences in SC thickness for the utilized methods. Therefore, the results indicate that it is possible to calculate the SC thickness by using the DNA profile in the fingerprint region, which is comparable with the SC thickness calculated by the water depth profiles (ANOVA test p = 0.77) and the lipid depth profile (ANOVA test p = 0.74). This provides the possibility to measure the SC thickness by using the DNA profile, in case the water or lipid profile analyses are influenced by a topically applied formulation. The increase in DNA concentration in the superficial SC (0-2 µm) is related to the DNA presence in the microbiome of the skin, which was not present in the SC depth below 4 µm.

Effects of Imprinted 3D Surface Patterning on Localized Changes in the Tribology of Human Stratum Corneum.

Natural surfaces may exhibit remarkable surface properties due to their structure. In the case of skin, its surface topography (microrelief) influences many of its perceived sensorial properties (shine, color, touch). Imprinted patterns can modify the original microrelief, inducing a completely new set of perceived properties. To explore the effects of superimposed biomimetic surface textures on the friction of skin, human stratum corneum was prepared with and without an imprinted regular, micrometer-sized, 3D grid pattern. Atomic Force Microscopy (AFM) and optical profilometry indicated that the inherent, smaller-scale roughness of the stratum corneum remained when lines with heights of 20-200 µm and spacings of 600-2000 µm were introduced, but it was somewhat reduced on the grid lines. Surface Forces Apparatus (SFA) friction experiments on stratum corneum were performed at low speed (µm/s, back-and-forth sliding) and at more realistic, high speed (cm/s, rotational sliding). Two stratum corneum surfaces in contact did not adhere to one another, and they had a friction coefficient µ of 0.1, or lower, at low sliding speed. An interesting loading-unloading hysteresis was observed, with lower friction force on unloading, in particular, when the contact was on a grid line of the patterned samples. This suggests that the patterning locally induced different mechanical properties of the stratum corneum and that its recovery was not immediate on unloading. When one stratum corneum surface slid against a rigid glass surface, the friction coefficient was always higher than that when two stratum corneum surfaces were in contact. At high sliding speed, much higher friction coefficients were found between one stratum corneum surface and a rigid, smooth surface, µ ≥ 1. The results demonstrate that topograpic patterning by imprinting clearly modifies the tribological response of stratum corneum. This approach provides a simple method for exploring the development of biomimetic modifications of skin texture.

3D imaging of human epidermis micromorphology by combining fluorescent dye, optical clearing and confocal microscopy.

BACKGROUND: The human epidermis presents a complex organization due to its dynamic and plein-stratified epithelium. Still nowadays, one of the best method to study this layer of the skin remains the histology sections. This approach remains tedious and gives only 2D information. MATERIALS AND METHODS: Rhodamine B is a dye known to have a high affinity for the epidermal layer and to possess fluorescent properties. Associated with a clarification method such as 3DiSCO, this dye maintains a high fluorescence emission. The skin which became transparent can then be investigated with a Laser Scanning Confocal Microscope. RESULTS: We showed that this technique can collect longitudinal or transversal optical sections of the epidermis as whole. Serial sections allowed to move easily into the epidermis. A 3D imaging can also be generated to study the microrelief of the stratum corneum or the complex organization of the dermal-epidermal junction. CONCLUSION: In this work, we describe a simple and fast staining and clearing method for skin samples. In association with a fluorescence microscope such as the confocal, we show a new way to characterize the whole epidermis. This work appears as a valuable and complementary method to understand several topics around skin investigation.

Comparison of ceramide retention in the stratum corneum between dry skin and normal skin using animal model with fluorescent imaging method.

BACKGROUND/PURPOSE: Skin care via moisturization compensates for the lack of skin barrier function. However, moisturizer application methods are not clearly decided. Here, we focused on and examined the retention of externally applied ceramide in the stratum corneum (SC) using fluorescent imaging method. This study aimed to compare ceramide retention in the SC between normal skin and dry skin using an animal model. METHODS: Nine-week-old Sprague-Dawley rats were divided into two groups: normal skin and dry skin model. The dry skin model group was treated with acetone-diethyl ether solution. A fluorescently labeled ceramide solution was prepared and applied to rats' back skin. Skin samples were taken at 0 minute and 12 hours after ceramide application. Fluorescently labeled ceramide was evaluated and observed under a microscope. RESULTS: The intensity of externally applied ceramide in the normal skin group showed no significant change from 0 minute to 12 hours after application. In contrast, in the dry skin model group, the intensity of externally applied ceramide increased significantly from 0 minute to 12 hours after application. CONCLUSION: Our findings demonstrate that the externally applied ceramide penetrated the SC of dry skin more than that of normal skin.

Noninvasive Determination of Epidermal and Stratum Corneum Thickness in vivo Using Two-Photon Microscopy and Optical Coherence Tomography: Impact of Body Area, Age, and Gender.

BACKGROUND: High-resolution images of the epidermis are important to understand the transdermal penetration and changes in epidermal components. Both ex vivo and in vivo technologies are available to picture the epidermal thickness (ET). So far, the illustration of the stratum corneum (SC) has not been possible without artifacts. OBJECTIVE: Precision in vivo measurement of the ET and SC, duly considering the impact of location on the body, age, and gender. METHODS: In this pilot study on 20 skin-healthy subjects aged 18-66 years, the ET was imaged by two-photon microscopy (2PM) and optical coherence tomography (OCT), and the SC by using 2PM at five different body sites. RESULTS: On solar-exposed body areas, both the epidermis and SC are thicker compared to solar-protected areas (p < 0.05), the epidermis at the gluteal region being the thickest (p < 0.05). The ET decreases with age (p < 0.05). Males show a thicker epidermis than females (p < 0.05). CONCLUSION: 2PM provides a noninvasive method for imaging the epidermis and especially the SC in vivo and is optimally suited for the application of histological criteria.

Characterisation of cholinesterases in mucous secretions and their localisation in epidermis of Labeo rohita and Cirrhinus mrigala.

Cholinesterases are multifunctional enzymes and have been associated with diverse physiological functions in addition to their classical role at synapses. In the present study, cholinesterase (ChE) isozymes have been characterised in mucous secretions and their activity has been localised in the epidermis of Labeo rohita and Cirrhinus mrigala. Zymography using specific substrates and inhibitors revealed the presence of two ChE isozymes-ChE-1 and ChE-2. The isozyme ChE-1 was characterised as an atypical butyrylcholinesterase and ChE-2 as a typical acetylcholinesterase in skin mucous secretions of both the fish species. Enzyme histochemical analysis demonstrated the presence of ChE activity in the epidermis of the fish species investigated. In both the fish species, strong ChE activity was observed in the outer-layer epithelial cells, taste buds and neuromasts. The middle and basal layer epithelial cells showed moderate to weak ChE activity. Club cells and mucous goblet cells showed the absence of ChE activity. Characterisation with specific inhibitors indicates that acetylcholinesterase (AChE) was the major cholinesterase type expressed in the epidermis of the two fish species investigated. Immunohistochemical localisation of apoptotic and cell proliferation markers, in addition, revealed high expression of active caspase 3 in the outer-layer epithelial cells, and proliferating cell nuclear antigen (PCNA) in the middle and basal layer epithelial cells. High ChE activity in caspase 3-positive cells in the outer layer of the epidermis and low in PCNA-positive cells in middle and basal layers could point towards the possible involvement of ChEs in cell death and their final extrusion from skin surface.

Genomic determinants of epidermal appendage patterning and structure in domestic birds.

Variation in regional identity, patterning, and structure of epidermal appendages contributes to skin diversity among many vertebrate groups, and is perhaps most striking in birds. In pioneering work on epidermal appendage patterning, John Saunders and his contemporaries took advantage of epidermal appendage diversity within and among domestic chicken breeds to establish the importance of mesoderm-ectoderm signaling in determining skin patterning. Diversity in chickens and other domestic birds, including pigeons, is driving a new wave of research to dissect the molecular genetic basis of epidermal appendage patterning. Domestic birds are not only outstanding models for embryonic manipulations, as Saunders recognized, but they are also ideal genetic models for discovering the specific genes that control normal development and the mutations that contribute to skin diversity. Here, we review recent genetic and genomic approaches to uncover the basis of epidermal macropatterning, micropatterning, and structural variation. We also present new results that confirm expression changes in two limb identity genes in feather-footed pigeons, a case of variation in appendage structure and identity.

A morphoanatomical approach to the adaptive features of the epidermis and proboscis of a marine Polychaeta: Eulalia viridis (Phyllodocida: Phyllodocidae).

Eulalia viridis is a marine Polychaeta of the rocky intertidal that, despite its simple anatomy, is an active predator of much larger invertebrates, from which it extracts pieces of soft tissue through suction. This uncanny feeding strategy triggered the pursuit for the morphological mechanisms that enable adaptation to its environment. The evaluation of the worm anatomy and microanatomy, combining electron and optical microscopy, revealed a series of particular adaptations in the epidermis and in the proboscis (the heavily muscled eversible pharynx). Besides its function in feeding, the proboscis is the main sensory organ, being equipped with numerous sensorial papillae holding chemoreceptors. Additionally, the proboscis possesses tentacles that become exposed when the organ is everted. These provide fast release of mucus and toxins, from mucocytes and special serous cells, respectively (the latter involving both merocrine and apocrine processes), whenever contact with a prey occurs. In its turn, the epidermis provides protection by cuticle and mucus secretion and has a sensorial function that may be associated to the worm's uncommon green pigment cells. Eulalia viridis presents a series of elegant adaptive tools to cope with its environment that are evolutionarily designed to counterbalance its relatively simple body plan.

VEGF, FGF-2 and TGFß expression in the normal and regenerating epidermis of geckos: implications for epidermal homeostasis and wound healing in reptiles.

The skin is a bilayered organ that serves as a key barrier between an organism and its environment. In addition to protecting against microbial invasion, physical trauma and environmental damage, skin participates in maintaining homeostasis. Skin is also capable of spontaneous self-repair following injury. These functions are mediated by numerous pleiotrophic growth factors, including members of the vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), and transforming growth factor ß (TGFß) families. Although growth factor expression has been well documented in mammals, particularly during wound healing, for groups such as reptiles less is known. Here, we investigate the spatio-temporal pattern of expression of multiple growth factors in normal skin and following a full-thickness cutaneous injury in the representative lizard Eublepharis macularius, the leopard gecko. Unlike mammals, leopard geckos can heal cutaneous wounds without scarring. We demonstrate that before, during and after injury, keratinocytes of the epidermis express a diverse panel of growth factor ligands and receptors, including: VEGF, VEGFR1, VEGFR2, and phosphorylated VEGFR2; FGF-2 and FGFR1; and phosphorylated SMAD2, TGFß1, and activin ßA. Unexpectedly, only the tyrosine kinase receptors VEGFR1 and FGFR1 were dynamically expressed, and only during the earliest phases of re-epithelization; otherwise all the proteins of interest were constitutively present. We propose that the ubiquitous pattern of growth factor expression by keratinocytes is associated with various roles during tissue homeostasis, including protection against ultraviolet photodamage and coordinated body-wide skin shedding.

Digital analysis yields more reliable and accurate measures of dermal and epidermal thickness in histologically processed specimens compared to traditional methods.

Changes in the thickness of the dermis and epidermis have been described in the scenario of tissue expansion as well as inflammatory skin processes (psoriasis, contact hypersensitivity and so on). These changes have previously been quantified using ocular micrometers to obtain and then average a limited number of spot measurements, leading to suboptimal accuracy. We describe a rapid method of using freely available ImageJ software to analyze digitized images of fixed skin specimens. By determining the cross-sectional area and surface length of a skin layer, a simple calculation produces more accurate and reproducible measurements of its thickness compared to historical methods, with excellent inter-rater reliability.

An explanation for the mysterious distribution of melanin in human skin: a rare example of asymmetric (melanin) organelle distribution during mitosis of basal layer progenitor keratinocytes.

BACKGROUND: Melanin is synthesized by melanocytes in the basal layer of the epidermis. When transferred to surrounding keratinocytes melanin is the key ultraviolet radiation-protective biopolymer responsible for skin pigmentation. Most melanin is observable in the proliferative basal layer of the epidermis and only sparsely distributed in the stratifying/differentiating epidermis. The latter has been explained as 'melanin degradation' in suprabasal layers. OBJECTIVES: To re-evaluate the currently accepted basis for melanin distribution in human epidermis and to discover whether this pattern is altered after a regenerative stimulus. METHODS: Normal epidermis of adult human skin, at rest and after tape-stripping, was analysed by a range of (immuno)histochemical and high-resolution microscopy techniques. In vitro models of melanin granule uptake by human keratinocytes were attempted. RESULTS: We propose a different fate for melanin in the human epidermis. Our evidence indicates that the bulk of melanin is inherited only by the nondifferentiating daughter cell postmitosis in progenitor keratinocytes via asymmetric organelle inheritance. Moreover, this preferred pattern of melanin distribution can switch to a symmetric or equal daughter cell inheritance mode under conditions of stress, including regeneration. CONCLUSIONS: In this preliminary report, we provide a plausible and histologically supported explanation for how human skin pigmentation is efficiently organized in the epidermis. Steady-state epidermis pigmentation may involve much less redox-sensitive melanogenesis than previously thought, and at least some premade melanin may be available for reuse. The epidermal melanin unit may be an excellent example with which to study organelle distribution via asymmetric or symmetric inheritance in response to microenvironment and tissue demands.

Somatotopic heat pain thresholds and intraepidermal nerve fibers in health.

INTRODUCTION: For sequential and somatotopic assessment of small fiber neuropathy, heat pain (HP) tests of hypoalgesia might be used instead of decreased counts of epidermal nerve fibers (ENFs), but then healthy subject reference values of HP thresholds are needed. METHODS: Using the Computer Assisted Sensation Evaluator IVc system, HP thresholds of hypoalgesia were estimated for 10 unilateral sites and counts of ENFs for 4 of them in healthy subjects. RESULTS: In healthy subjects, small but statistically significant differences of both HP thresholds of hypoalgesia and counts of ENFs were observed among tested sites. Significant correlations between HP thresholds and counts of ENFs were not found. DISCUSSION: For the studied somatotopic sites, we provide ≥95th and ≥99th percentile reference limits for HP 0.5 and 5 of 1-10 HP thresholds of hypoalgesia and decreased counts of ENFs at ≤5th and ≤1st percentile levels. Muscle Nerve 58: 509-516, 2018.

Three-dimensional digital reconstruction of skin epidermis and dermis.

This study describes how three-dimensional (3D) human skin tissue is reconstructed, and provides digital anatomical data for the physiological structure of human skin tissue based on large-scale thin serial sections. Human skin samples embedded in paraffin were cut serially into thin sections and then stained with hematoxylin-eosin. Images of serial sections obtained from lighting microscopy were scanned and aligned by the scale-invariant feature transform algorithm. 3D reconstruction of the skin tissue was generated using Mimics software. Fibre content, porosity, average pore diameter and specific surface area of dermis were analysed using the ImageJ analysis system. The root mean square error and mutual information based on the scale-invariant feature transform algorithm registration were significantly greater than those based on the manual registration. Fibre distribution gradually decreased from top to bottom; while porosity showed an opposite trend with irregular average pore diameter distribution. A specific surface area of the dermis showed a 'V' shape trend. Our data suggested that 3D reconstruction of human skin tissue based on large-scale serial sections could be a valuable tool for providing a highly accurate histological structure for analysis of skin tissue. Moreover, this technology could be utilized to produce tissue-engineered skin via a 3D bioprinter in the future.

The skin immune response of rainbow trout, Oncorhynchus mykiss (Walbaum), associated with puffy skin disease (PSD).

Puffy skin disease (PSD) is an emerging skin condition which affects rainbow trout, Oncorhynchus mykiss (Walbaum). The transmission pattern of PSD suggests an infectious aetiology, however, the actual causative infectious agent(s) remain(s) unknown. In the present study, the rainbow trout epidermal immune response to PSD was characterised. Skin samples from infected fish were analysed and classified as mild, moderate or severe PSD by gross pathology and histological assessment. The level of expression of 26 immune-associated genes including cytokines, immunoglobulins and cell markers were examined by TaqMan qPCR assays. A significant up-regulation of the gene expression of C3, lysozyme, IL-1ß and T-bet and down-regulation of TGFß and TLR3 was observed in PSD fish compared to control fish. MHCI gene expression was up-regulated only in severe PSD lesions. Histological examinations of the epidermis showed a significant increase in the number of eosinophil cells and dendritic melanocytes in PSD fish. In severe lesions, mild diffuse lymphocyte infiltration was observed. IgT and CD8 positive cells were detected locally in the skin of PSD fish by in situ hybridisation (ISH), however, the gene expression of those genes was not different from control fish. Total IgM in serum of diseased animals was not different from control fish, measured by a sandwich ELISA, nor was significant up regulation of IgM gene expression in PSD lesions observed. Taken together, these results show activation of the complement pathway, up-regulation of a Th17 type response and eosinophilia during PSD. This is typical of a response to extracellular pathogens (i.e. bacteria and parasites) and allergens, commonly associated with acute dermatitis.