ICAM-1 nanoclusters regulate hepatic epithelial cell polarity by leukocyte adhesion-independent control of apical actomyosin.

Epithelial intercellular adhesion molecule (ICAM)-1 is apically polarized, interacts with, and guides leukocytes across epithelial barriers. Polarized hepatic epithelia organize their apical membrane domain into bile canaliculi and ducts, which are not accessible to circulating immune cells but that nevertheless confine most of ICAM-1. Here, by analyzing ICAM-1_KO human hepatic cells, liver organoids from ICAM-1_KO mice and rescue-of-function experiments, we show that ICAM-1 regulates epithelial apicobasal polarity in a leukocyte adhesion-independent manner. ICAM-1 signals to an actomyosin network at the base of canalicular microvilli, thereby controlling the dynamics and size of bile canalicular-like structures. We identified the scaffolding protein EBP50/NHERF1/SLC9A3R1, which connects membrane proteins with the underlying actin cytoskeleton, in the proximity interactome of ICAM-1. EBP50 and ICAM-1 form nano-scale domains that overlap in microvilli, from which ICAM-1 regulates EBP50 nano-organization. Indeed, EBP50 expression is required for ICAM-1-mediated control of BC morphogenesis and actomyosin. Our findings indicate that ICAM-1 regulates the dynamics of epithelial apical membrane domains beyond its role as a heterotypic cell-cell adhesion molecule and reveal potential therapeutic strategies for preserving epithelial architecture during inflammatory stress.

Acid-Sensing Ion Channels' Immunoreactivity in Nerve Profiles and Glomus Cells of the Human Carotid Body.

The carotid body is a major peripheral chemoreceptor that senses changes in arterial blood oxygen, carbon dioxide, and pH, which is important for the regulation of breathing and cardiovascular function. The mechanisms by which the carotid body senses O2 and CO2 are well known; conversely, the mechanisms by which it senses pH variations are almost unknown. Here, we used immunohistochemistry to investigate how the human carotid body contributes to the detection of acidosis, analyzing whether it expresses acid-sensing ion channels (ASICs) and determining whether these channels are in the chemosensory glomic cells or in the afferent nerves. In ASIC1, ASIC2, and ASIC3, and to a much lesser extent ASIC4, immunoreactivity was detected in subpopulations of type I glomus cells, as well as in the nerves of the carotid body. In addition, immunoreactivity was found for all ASIC subunits in the neurons of the petrosal and superior cervical sympathetic ganglia, where afferent and efferent neurons are located, respectively, innervating the carotid body. This study reports for the first time the occurrence of ASIC proteins in the human carotid body, demonstrating that they are present in glomus chemosensory cells (ASIC1 < ASIC2 > ASIC3 > ASIC4) and nerves, presumably in both the afferent and efferent neurons supplying the organ. These results suggest that the detection of acidosis by the carotid body can be mediated via the ASIC ion channels present in the type I glomus cells or directly via sensory nerve fibers.

Pacinian Corpuscles as a Diagnostic Clue of Ledderhose Disease-A Case Report and Mapping of Pacinian Corpuscles of the Sole.

BACKGROUND: Plantar fibromatosis, known as Ledderhose disease, is a neoplastic disease characterized by a locally-aggressive bland fibroblastic proliferation. Although Pacinian corpuscles alterations are commonly described in palmar fibromatosis, there are still no references about Pacinian corpuscles alterations in the rarer plantar version. METHODS: We present a case report where a wide cutaneous resection, including the plantar fascia was performed, allowing a detailed study of Pacinian corpuscles. Pacinian corpuscles were analyzed using immunohistochemistry for neurofilament proteins, S100 protein, CD34, vimentin, glucose transporter 1, epithelial membrane antigen, neural-cell adhesion molecule, actin, desmin, type IV collagen, and high-affinity neurotrophin Trk-receptors. Moreover, the density and the size of the corpuscles were determined. RESULTS: A clear increase in the number (hyperplasia) of Pacinian corpuscles was evidenced in the Ledderhose disease plantar fascia in comparison with similarly aged normal subjects. Pacinian hypertrophy was not demonstrated, but a significant decrease in the number of corpuscular lamellae was noted, with a subsequent increase in the interlamellar spaces. Pacinian corpuscles from the pathological plantar fascia showed an abnormal structure and immunohistochemical profile, generally without identifiable axons, and also absence of an inner core or an intermediate layer. Moreover, other molecules related with trophic maintenance of corpuscles were also absent. Finally, a vascular proliferation was commonly noted in some corpuscles, which involved all corpuscular constituents. CONCLUSION: The observed Pacinian corpuscles hyperplasia could be considered a diagnostic clue of plantar fibromatosis.

Merkel Cell Carcinoma Display PIEZO2 Immunoreactivity.

As an essential component of mechano-gated ion channels, critically required for mechanotransduction in mammalian cells, PIEZO2 is known to be characteristically expressed by Merkel cells in human skin. Here, we immunohistochemically investigated the occurrence of Piezo channels in a case series of Merkel cell carcinoma. A panel of antibodies was used to characterize Merkel cells, and to detect PIEZO2 expression. All analyzed tumors displayed PIEZO2 in nearly all cells, showing two patterns of immunostaining: membranous and perinuclear dot-like. PIEZO2 co-localized with cytokeratin 20, chromogranin A, synaptophysin and neurofilament. Moreover, neurofilament immunoreactive structures resembling nerve-Merkel cell contacts were occasionally found. PIEZO2 was also detected in cells of the sweat ducts. The role of PIEZO2 in Merkel cell carcinoma is still unknown, but it could be related with the mechanical regulation of the tumor biology or be a mere vestige of the Merkel cell derivation.

The acquisition of mechanoreceptive competence by human digital Merkel cells and sensory corpuscles during development: An immunohistochemical study of PIEZO2.

BACKGROUND: PIEZO2 is a transmembrane protein forming part of an ion channel required for mechanotransduction. In humans, PIEZO2 is present in axon terminals of adult Meissner and Pacinian corpuscles, as well as Merkel cells in Merkel cell-neurite complexes. METHODS: To study the acquisition of functional capability for mechanotransduction of developing type I slowly adapting low-threshold mechanoreceptors, i.e., Merkel cell-neurite complexes, a battery of immunohistochemical and immunofluorescence techniques was performed on human skin specimens covering the whole development and growth, from 11 weeks of estimated gestational age to 20 years of life. In addition, developmental expression of PIEZO2 type I (Meissner's corpuscles) and type II (Pacinian corpuscles) rapidly adapting mechanoreceptors was studied in parallel. RESULTS: The first evidence of Merkel cells showing the typical morphology and placement was at 13 weeks of estimated gestation age, and at this time positive immunoreactivity for PIEZO2 was achieved. PIEZO2 expression in axons terminals started at 23 WEGA in Pacinian corpuscles and at 36 WEGA in the case of Meissner corpuscles. The occurrence of PIEZO2 in Merkel cells, Meissner and Pacinian corpuscles was maintained for all the time investigated. Interestingly PIEZO2 was absent in most Aß type I slowly adapting low-threshold mechanoreceptors that innervate MC while it was regularly present in most Aß type I and type II rapidly adapting low-threshold mechanoreceptors that supplies Meissner and Pacinian corpuscles. CONCLUSION: The present results provide evidence that human cutaneous mechanoreceptors could perform mechanotransduction already during embryonic development.

Synaptophysin is a selective marker for axons in human cutaneous end organ complexes.

BACKGROUND: Small clear synaptic-like vesicles fill axon terminals of mechanoreceptors. Their functional significance is controversial and probably includes release of neurotransmitters from afferent axon terminals. Synaptophysin, a major protein of the synaptic vesicle membrane, is present in presynaptic endings of the central and peripheral nervous systems. It is also expressed in mechanosensory neurons which extend into skin forming sensory corpuscles. Nevertheless, synaptophysin occurrence in these structures has never been investigated. METHODS: Here we used immunohistochemistry to detect synaptophysin in adult human dorsal root ganglia, cutaneous Meissner and Pacinian corpuscles and Merkel cell-neurite complexes from foetal to elderly period. Moreover, we analyzed whether synaptophysin co-localizes with the mechano-gated protein PIEZO2. RESULTS: Synaptophysin immunoreactivity was observed in primary sensory neurons (36 ± 6%) covering the entire soma size ranges. Axons of Meissner's and Pacinian corpuscles were positive for synaptophysin from 36 and 12 weeks of estimated gestational age respectively, to 72 years old. Synaptophysin was also detected in Merkel cells (from 14 weeks of estimated gestational age to old age). Additionally in adult skin, synaptophysin and PIEZO2 co-localized in the axon of Meissner and Pacinian corpuscles, Merkel cells as well as in some axons of Merkel cell-neurite complexes. CONCLUSION: Present results demonstrate that a subpopulation of primary sensory neurons and their axon terminals forming cutaneous sensory corpuscles contain synaptophysin, a typical presynaptic vesicle protein. Although the functional relevance of these findings is unknown it might be related to neurotransmission mechanisms linked to mechanotransduction.

Plasmolipin regulates basolateral-to-apical transcytosis of ICAM-1 and leukocyte adhesion in polarized hepatic epithelial cells.

Apical localization of Intercellular Adhesion Receptor (ICAM)-1 regulates the adhesion and guidance of leukocytes across polarized epithelial barriers. Here, we investigate the molecular mechanisms that determine ICAM-1 localization into apical membrane domains of polarized hepatic epithelial cells, and their effect on lymphocyte-hepatic epithelial cell interaction. We had previously shown that segregation of ICAM-1 into apical membrane domains, which form bile canaliculi and bile ducts in hepatic epithelial cells, requires basolateral-to-apical transcytosis. Searching for protein machinery potentially involved in ICAM-1 polarization we found that the SNARE-associated protein plasmolipin (PLLP) is expressed in the subapical compartment of hepatic epithelial cells in vitro and in vivo. BioID analysis of ICAM-1 revealed proximal interaction between this adhesion receptor and PLLP. ICAM-1 colocalized and interacted with PLLP during the transcytosis of the receptor. PLLP gene editing and silencing increased the basolateral localization and reduced the apical confinement of ICAM-1 without affecting apicobasal polarity of hepatic epithelial cells, indicating that ICAM-1 transcytosis is specifically impaired in the absence of PLLP. Importantly, PLLP depletion was sufficient to increase T-cell adhesion to hepatic epithelial cells. Such an increase depended on the epithelial cell polarity and ICAM-1 expression, showing that the epithelial transcytotic machinery regulates the adhesion of lymphocytes to polarized epithelial cells. Our findings strongly suggest that the polarized intracellular transport of adhesion receptors constitutes a new regulatory layer of the epithelial inflammatory response.

Human digital merkel cells display pannexin1 immunoreactivity.

Pannexins are channel proteins displaying functional similarities to gap junctions in vertebrates and are regarded as transmembrane ATP-releasing channels. A member of this family, denominate pannexin1, has been detected in the epidermis and cutaneous adnexal structures. Here we used immunohistochemistry to investigate whether human digital Merkel cells express this protein since ATP is postulated as a neurotransmitter in the Merkel cell-axon complexes low-threshold mecahoreceptors. Pannexin1 immunoreactivity was found in cytokeratine 20-, chromogranin A- and synaptophysin-positive cells placed at the basal layer of the epidermis. Cell displaying pannexin1 immunoreactivities were thus identified as Merkel cells and showed close contact with nerve profiles. Light pannexin1 immunoreactivity in dermal blood vessels was also verified. Present results demonstrate for the first time the expression of pannexin1 in human digital Merkel cells supporting the idea that ATP can be involved directly or indirectly in the mechanotransductional process at Merkel-axon complexes.

Efficacy and safety of cold versus hot snare polypectomy for small (5-9 mm) colorectal polyps: a multicenter randomized controlled trial.

BACKGROUND: Resection techniques for small polyps include cold snare polypectomy (CSP) and hot snare polypectomy (HSP). This study compared CSP and HSP in 5-9 mm polyps in terms of complete resection and adverse events. METHODS: This was a multicenter, randomized trial conducted in seven Spanish centers between February and November 2019. Patients with ≥ 1 5-9 mm polyp were randomized to CSP or HSP, regardless of morphology or pit pattern. After polypectomy, two marginal biopsies were submitted to a pathologist who was blinded to polyp histology. Complete resection was defined as normal mucosa or burn artifacts in the biopsies. Abdominal pain was only assessed in patients without < 5 mm or > 9 mm polyps. RESULTS: 496 patients were randomized: 237 (394 polyps) to CSP and 259 (397 polyps) to HSP. Complete polypectomy rates were 92.5 % with CSP and 94.0 % with HSP (difference 1.5 %, 95 % confidence interval -1.9 % to 4.9 %). Intraprocedural bleeding occurred during three CSPs (0.8 %) and seven HSPs (1.8 %) (P = 0.34). One lesion per group (0.4 %) presented delayed hemorrhage. Post-colonoscopy abdominal pain presented similarly in both groups 1 hour after the procedure (CSP 18.8 % vs. HSP 18.4 %) but was higher in the HSP group after 5 hours (5.9 % vs. 16.5 %; P = 0.02). A higher proportion of patients were asymptomatic 24 hours after CSP than after HSP (97 % vs. 86.4 %; P = 0.01). CONCLUSIONS: We observed no differences in complete resection and bleeding rates between CSP and HSP. CSP reduced the intensity and duration of post-colonoscopy abdominal pain.

Sensory innervation of the human palmar aponeurosis in healthy individuals and patients with palmar fibromatosis.

The human palmar aponeurosis is involved in hand proprioception, and it contains different sensory corpuscle morphotypes that serve this role. In palmar fibromatosis (classically referred to as Dupuytren's disease), the palmar aponeurosis undergoes fibrous structural changes that, presumably, also affect the nervous system, causing altered perception. We analysed the various sensory nerve formation morphotypes in the palmar aponeuroses of healthy subjects and patients with palmar fibromatosis. To do this, we used immunohistochemistry for corpuscular constituents and the putative mechanoproteins PIEZO2 and acid-sensing ion channel 2. Free nerve endings and Golgi-Mazzoni, Ruffini, paciniform and Pacinian corpuscles were identified in both the healthy and the pathological conditions. The densities of the free nerve endings and Golgi-Mazzoni corpuscles were slightly increased in the pathological tissues. Furthermore, the Pacinian corpuscles were enlarged and displayed an altered shape. Finally, there was also morphological and immunohistochemical evidence of occasional denervation of the Pacinian corpuscles, although no increase in their number was observed. Both PIEZO2 and acid-sensing ion channel 2 were absent from the altered corpuscles. These results indicate that the human palmar aponeurosis is richly innervated, and the free nerve endings and sensory corpuscles within the palmar aponeurosis undergo quantitative and qualitative changes in patients with palmar fibromatosis, which may explain the sensory alterations occasionally reported for this pathology.

Transdermal Drug Delivery in the Pig Skin.

Transdermal delivery can be accomplished through various mechanisms including formulation optimization, epidermal stratum corneum barrier disruption, or directly by removing the stratum corneum layer. Microneedling, electroporation, a combination of both and also the intradermal injection known as mesotherapy have proved efficacy in epidermal-barrier disruption. Here we analyzed the effects of these methods of epidermal-barrier disruption in the structure of the skin and the absorption of four compounds with different characteristics and properties (ketoprofen, biotin, caffein, and procaine). Swine skin (Pietrain x Durox) was used as a human analogue, both having similar structure and pharmacological release. They were biopsied at different intervals, up to 2 weeks after application. High-pressure liquid chromatography and brightfield microscopy were performed, conducting a biometric analysis and measuring histological structure and vascular status. The performed experiments led to different results in the function of the studied molecules: ketoprofen and biotin had the best concentrations with intradermal injections, while delivery methods for obtaining procaine and caffein maximum concentrations changed on the basis of the lapsed time. The studied techniques did not produce significant histological alterations after their application, except for an observed increase in Langerhans cells and melanocytes after applying electroporation, and an epidermal thinning after using microneedles, with variable results regarding dermal thickness. Although all the studied barrier disruptors can accomplish transdermal delivery, the best disruptor is dependent on the particular molecule.

Involvement of Cutaneous Sensory Corpuscles in Non-Painful and Painful Diabetic Neuropathy.

Distal diabetic sensorimotor polyneuropathy (DDSP) is the most prevalent form of diabetic neuropathy, and some of the patients develop gradual pain. Specialized sensory structures present in the skin encode different modalities of somatosensitivity such as temperature, touch, and pain. The cutaneous sensory structures responsible for the qualities of mechanosensitivity (fine touch, vibration) are collectively known as cutaneous mechanoreceptors (Meissner corpuscles, Pacinian corpuscles, and Merkel cell-axonal complexes), which results are altered during diabetes. Here, we used immunohistochemistry to analyze the density, localization within the dermis, arrangement of corpuscular components (axons and Schwann-like cells), and expression of putative mechanoproteins (PIEZO2, ASIC2, and TRPV4) in cutaneous mechanoreceptors of subjects suffering clinically diagnosed non-painful and painful distal diabetic sensorimotor polyneuropathy. The number of Meissner corpuscles, Pacinian corpuscles, and Merkel cells was found to be severely decreased in the non-painful presentation of the disease, and almost disappeared in the painful presentation. Furthermore, there was a marked reduction in the expression of axonal and Schwann-like cell markers (with are characteristics of corpuscular denervation) as well as of all investigated mechanoproteins in the non-painful distal diabetic sensorimotor polyneuropathy, and these were absent in the painful form. Taken together, these alterations might explain, at least partly, the impairment of mechanosensitivity system associated with distal diabetic sensorimotor polyneuropathy. Furthermore, our results support that an increasing severity of DDSP may increase the risk of developing painful neuropathic symptoms. However, why the absence of cutaneous mechanoreceptors is associated with pain remains to be elucidated.

TP53 Abnormalities and MMR Preservation in 5 Cases of Proliferating Trichilemmal Tumours.

Proliferating trichilemmal tumours (PTT) are defined by a benign squamous cell proliferation inside a trichilemmal cystic (TC) cavity. A possible explanation of this proliferative phenomenon within the cyst may be molecular alterations in genes associated to cell proliferation, which can be induced by ultraviolet radiation. Among other genes, alterations on TP53 and DNA mismatch repair proteins (MMR) may be involved in the cellular proliferation observed in PTT. Based on this assumption, but also taking into account the close relationship between the sebaceous ducts and the external root sheath where TC develop, a MMR, a p53 expression assessment and a TP53 study were performed in a series of 5 PTT cases, including a giant one. We failed to demonstrate a MMR disorder on studied PTT, but we agree with previous results suggesting increased p53 expression in these tumours, particularly in proliferative areas. TP53 alteration was confirmed with FISH technique, demonstrating TP53 deletion in most cells.

Sensory innervation of the human male prepuce: Meissner's corpuscles predominate.

Meissner's corpuscles are the most abundant sensory corpuscles in the glabrous skin of the male prepuce. They are type I, rapidly adapting, low-threshold mechanoreceptors, and their function is linked to the expression of the mechanoprotein piezo-type mechanosensitive ion channel component 2 (PIEZO2). Stimulation of genital Meissner's corpuscles gives rise to sexual sensations. It has been recently demonstrated that digital Meissner's corpuscles, Meissner-like corpuscles, and genital end bulbs have an endoneurium-like capsule surrounding their neuronal elements; that is, the axon and glial lamellar cells, and their axons, display PIEZO2 immunoreactivity. It is unknown whether this is also the case for preputial Meissner's corpuscles. Furthermore, the expression of certain proteins that have been found in Meissner's corpuscles at other anatomical locations, especially in the digits, has not been investigated in preputial Meissner's corpuscles. Here, we used immunohistochemistry to investigate the expression of axonal (neurofilament, neuron-specific enolase), glial (S100 protein, glial fibrillary acidic protein, vimentin), endoneurial (CD34), and perineurial (glucose transporter 1) markers in the preputial and digital Meissner's corpuscles of male participants aged between 5 and 23 years. Furthermore, we investigated the occurrence of the mechanoprotein PIEZO2 in male preputial Meissner's corpuscles. Human male prepuce contains numerous Meissner's corpuscles, which may be grouped or isolated and are regularly distributed in the dermal papillae. Lamellar glial cells display strong expression of S100 protein and vimentin but lack expression of glial fibrillary acidic protein. In addition, they show axonal PIEZO2 expression and have an endoneurial capsule, but no perineurial. Our results indicate that human male preputial Meissner's corpuscles share the immunohistochemical profile of digital Meissner's corpuscles, which is considered to be necessary for mechanotransduction. These data strongly suggest that the structure and function of Meissner's corpuscles are independent of their anatomical location.

Glans clitoris innervation: PIEZO2 and sexual mechanosensitivity.

The clitoris is a leading player in female sexual arousal, if not the main protagonist. Despite this role, studies performed on this structure with specific neuroanatomical techniques are few. This study focuses on glans clitoris innervation, with special emphasis on sensory corpuscles and the presence of the mechanotransducer protein PIEZO2 in these structures. Six glans clitoris samples were obtained at autopsy covering an age spectrum between 52 and 83 years old. Several types of nerve terminations including free nerve endings, genital endbulbs as well as Meissner-like corpuscles and Pacinian corpuscles, but not Ruffini corpuscles, were found. Although corpuscular morphology in the glans clitoris was subtly different from the cutaneous digital counterparts, their basic composition was comparable for both Pacinian and Meissner-like corpuscles. Genital endbulbs showed heterogeneous morphology, and the axons usually exhibited a typical "wool ball" or "yarn ball" aspect. Some of them were lobulated and variably encapsulated by endoneurial elements (65%); from the capsule originate septa that divides the genital endbulbs, suggesting that they are found in clusters rather than as single corpuscles. In addition, most corpuscles in the glans clitoris showed axonal PIEZO2 immunoreactivity, thus, suggesting a mechanical role and molecular mechanisms of mechanosensibility similar to those of digital Meissner's corpuscles. Our results demonstrate that sensory corpuscles of the glans clitoris are similar to those of other glabrous skin zones, as most genital organs are characterized by clusters of corpuscles and the occurrence of the mechanoprotein PIEZO2 in the axons. These findings strongly suggest that PIEZO2 participates in erotic and sexual mechanical sensing.

Verification and characterisation of human digital Ruffini's sensory corpuscles.

Ruffini's corpuscles are present as long fusiform encapsulated sensory structures in different tissues including the skin. Although physiological analyses strongly suggest their existence in glabrous digital skin, such localisation remains unconfirmed. Here, we have investigated the occurrence of typical Ruffini's corpuscles in 372 sections of human digital skin obtained from 186 subjects of both sexes and different ages (19-92 years). S100 protein, neuron-specific enolase and neurofilament proteins were detected, and the basic immunohistochemical profile of these corpuscles was analysed. Fewer than 0.3 Ruffini's corpuscles/mm2 were detected, with density distribution across the fingers being F4 > F3 > F2 > F1 > F5 and absolute values being F2 > F1 > F3 > F4 > F5. Axons displayed neuron-specific enolase immunoreactivity, glial cells forming the core contained S100 protein, and the capsule was positive for CD34 but not Glut1, demonstrating an endoneurial origin. Present results demonstrate the existence of Ruffini's corpuscles in human glabrous digital skin at very low densities. Moreover, the identified Ruffini's corpuscles share the basic immunohistochemical characteristics of other dermal sensory corpuscles.

Peripheral Mechanobiology of Touch-Studies on Vertebrate Cutaneous Sensory Corpuscles.

The vertebrate skin contains sensory corpuscles that are receptors for different qualities of mechanosensitivity like light brush, touch, pressure, stretch or vibration. These specialized sensory organs are linked anatomically and functionally to mechanosensory neurons, which function as low-threshold mechanoreceptors connected to peripheral skin through Aß nerve fibers. Furthermore, low-threshold mechanoreceptors associated with Aδ and C nerve fibers have been identified in hairy skin. The process of mechanotransduction requires the conversion of a mechanical stimulus into electrical signals (action potentials) through the activation of mechanosensible ion channels present both in the axon and the periaxonal cells of sensory corpuscles (i.e., Schwann-, endoneurial- and perineurial-related cells). Most of those putative ion channels belong to the degenerin/epithelial sodium channel (especially the family of acid-sensing ion channels), the transient receptor potential channel superfamilies, and the Piezo family. This review updates the current data about the occurrence and distribution of putative mechanosensitive ion channels in cutaneous mechanoreceptors including primary sensory neurons and sensory corpuscles.

Heparan sulfate in human cutaneous Meissner's and Pacinian corpuscles.

Heparan sulfate proteoglycans are pericellular/cell surface molecules involved in somatosensory axon guidance in the peripheral nervous system. However, the distribution of heparan sulfate proteoglycans in the extracellular matrix of human cutaneous sensory corpuscles is unknown. Immunohistochemistry and immunofluorescence assays were performed to define the localization of heparan sulfate proteoglycans in human cutaneous Meissner's and Pacinian corpuscles using two anti-heparan sulfate antibodies together with anti-S100 protein, anti-PGP9.5, anti-CD34 (to immunolabel basement membranes, Schwann cells, axon and the intermediate endoneurial layer of Pacinian corpuscles, respectively), anti-Type IV collagen, and anti-chondroitin sulfate antibodies. Heparan sulfate proteoglycans were colocalized with Type IV collagen in Meissner's corpuscles and were located in the outer core lamellae and capsule, but not in the inner core or the intermediate layer, in Pacinian corpuscles. Chondroitin sulfate was observed in the intermediate layer of Pacinian corpuscles but was never colocalized with heparan sulfate proteoglycans. The present results strongly suggest that heparan sulfate proteoglycans are associated with the basement membranes of the lamellar cells in Meissner's corpuscles and with the complex outer core capsule in Pacinian corpuscles. The functional significance of these results, if any, remains to be elucidated.

The capsule of human Meissner corpuscles: immunohistochemical evidence.

Meissner corpuscles are cutaneous mechanoreceptors that are usually located in the dermal papillae of human glabrous skin. Structurally, these sensory corpuscles consist of a mechanoreceptive sensory neuron surrounded by non-myelinating lamellar Schwann-like cells. Some authors have described a partially developed fibroblastic capsule of endoneurial or perineurial origin around Meissner corpuscles; however, others have noted that these structures are non-encapsulated. As there is continuity between the periaxonic cells forming the sensory corpuscles and the cells of the nerve trunks, we used immunohistochemistry to examine the expression of endoneurial (CD34 antigen) or perineurial [Glucose transporter 1 (Glut1)] markers in human cutaneous Meissner corpuscles. We also investigated the immunohistochemical patterns of nestin and vimentin (the main intermediate filaments of the cytoskeleton of endoneurial and perineurial cells, respectively) in Meissner corpuscles. The most important finding from this study was that CD34-positive cells formed a partial/complete capsule of endoneurial origin around most Meissner corpuscles, without signs of other perineurial Glut1-positive elements. However, the cytoskeletal proteins of the capsular CD34-positive cells did not include either nestin or vimentin, so the cytoskeletal composition of these cells remains to be established. Finally, the intensity of the immunoreactivity for CD34 in the capsule decreased with ageing, sometimes becoming completely absent in the oldest individuals. In conclusion, we report the first immunohistochemical evidence of the capsule of Meissner corpuscles in humans and demonstrate the endoneurial origin of the capsule.