Immunology
M. Alan Menter, Caitriona Ryan in Psoriasis, 2017
Langerhans cells are a type of immature conventional DC that reside in the epidermis.7 They are actively phagocytic and contain large granules known as Birbeck granules. CD1a and langerin (CD207) are used as specific markers to distinguish Langerhans cells from other DC subsets. The main role of Langerhans cells is to take up and process antigens and migrate to local skin-draining lymph nodes where they present to antigen-specific T cells.2 However, the role of Langerhans cells in psoriasis immunopathogenesis is still unclear.3 Recently, attention has focused on the potential importance of Langerhans cells in uninvolved skin sites of psoriasis patients, and it has been demonstrated that Langerhans cell migration is impaired in early onset psoriasis (onset before 40 years of age).31,32 Also, the treatment with TNF-α inhibitors (adalimumab, etanercept) and anti-IL-12p40 antibody (ustekinumab) significantly restored epidermal Langerhans cell migration in uninvolved skin.33 Although the influence of impaired Langerhans cell mobilization on the pathogenesis of psoriasis is uncertain, the loss of Langerhans cell motility may have an impact on the ability of these cells to sense the local antigenic microenvironment and regulate cutaneous immune responses.
Structure, Function, Type, and Sensitivity of Skin
Frank C. Powell, Jonathan Wilkin in Rosacea: Diagnosis and Management, 2008
Langerhans cells are immunologically competent cells of the epidermis found scattered just above the basal cells. These cells were first described by Paul Langerhans in 1868 when he was still a medical student, but their function remained unknown until fairly recently. They have long “dendritic” processes that form an extensive branching network in the suprabasal epidermis (Fig. 6). The purpose of this dendritic network of immune competent cells appears to be the trapping, processing, and the presentation of antigens to lymphocytes migrating from the dermal blood vessels. Langerhans cells “orchestrate” the complex cutaneous immune response to foreign matter. They also have an important role in cutaneous cancer surveillance. They are depleted by ultraviolet light and this possibly contributes to the susceptibility of skin malignancies developing in patients who have a lot of sun exposure.
Eczema (dermatitis)
Ronald Marks, Richard Motley in Common Skin Diseases, 2019
The sensitizing chemical (antigen) crosses the stratum corneum barrier and is picked up by the Langerhans cells in the epidermis (Fig. 10.24). The antigen is then ‘processed’ by the Langerhans cell and passed on to T-lymphocytes in the peripheral lymph nodes. Here, some of the T-lymphocytes develop a specific ‘memory’ for the particular antigen and the population of these expands. This process of sensitization takes some 10–14 days in humans. After this period, when the particular antigen contacts the skin once again, the primed T-lymphocytes with the ‘memory’ for this chemical species rush to the contacted site, and liberate cytokines and mediators that injure the epidermis and cause the eczematous reaction.
The use of in vivo reflectance confocal microscopy for the diagnosis of melanoma
Published in Expert Review of Anticancer Therapy, 2019
Marina Agozzino, Elvira Moscarella, Graziella Babino, Stefano Caccavale, Vincenzo Piccolo, Giuseppe Argenziano
MM is characterized by four major RCM clues: presence of pagetoid bright cells in the mucosal epithelium (roundish or spindle shaped with plump body), high density of basal hyper-reflective dendritic cells, loss of normal architecture of the chorion papillae and sheet-like proliferation of atypical cells [47,48]. The diagnosis of advanced melanoma is made promptly (Figure 4). The diagnosis of early invasive MM can be very difficult also with RCM because the architecture of the epithelium and the epithelium-chorion junction can be mostly preserved and only a few atypical melanocytes can be observed. Moreover, hyper-reflective dendritic cells can also correspond to Langerhans cells, frequently found in inflamed and even normal mucosa. Some benign melanoses present Langerhans cells around the chorion papillae and among the papillae and in the upper layers of the epithelium. In benign melanoses, roundish large medium-reflective cells corresponding to melanophages can be also seen inside the papillae [49–51]. When melanophages are present, they are usually numerous and can be distinguished from an initial spread of melanocytes towards the chorion, because they are less reflective and associated with edged-papillae and a normal epithelium that is not found in case of invasive melanoma. Moreover, the presence of a homogeneous hyper-reflective rim around the papillae is usually not found in melanoma and favors the diagnosis of melanosis.
Nanocrystal: a novel approach to overcome skin barriers for improved topical drug delivery
Published in Expert Opinion on Drug Delivery, 2018
Viral Patel, Om Prakash Sharma, Tejal Mehta
Apart from keratinocytes, melanocytes, Langerhans, and Merkel cells are also present in the epidermis. Melanocytes are the cells that have a potential to secrete a pigment known as melanin. They originate from the neural crest and are dopa-positive cells. Melanin is stored in the special cell organelle known as melanosome and is transported by structures called dendrites to keratinocytes [36]. Similar to the melanocytes, few cells are also present which lack pigment secretion and are dopa negative, known as the Langerhans cells. They were first identified, by a scientist named Langerhans, by staining the human epidermis with gold chloride [37]. This epidermal Langerhans cells originate in the bone marrow and migrate toward the skin epidermis via blood vessel walls of the dermis [38]. In epidermis, the Langerhans cells perform the function of antigen-presenting cells. They uptake the antigens from the skin and migrate toward the regional lymph nodes and activate the T cells, which help in fighting the skin infections. Merkel cells are positioned on the basal epidermal layer in touch-sensitive areas; thus, they are also called as touch cells or Tastzellen [39,39].
Site-specific drug delivery in the skin for the localized treatment of skin diseases
Published in Expert Opinion on Drug Delivery, 2019
Yang Chen, Xun Feng, Shengnan Meng
Underneath the epidermis lies the dermis, a 1–2 mm layer composed mainly of fibroblasts in an extracellular matrix of collagen and elastic fiber. It can be divided into the superficial papillary layer, and the lower reticular layer. The dermis layer comprises the bulk of the skin, and it also contains hair follicles, sweat glands, sebaceous glands, sensory nerve endings, lymphatic vessels, and blood capillaries, as well as immune cells including dermal dendritic cells, macrophages, T cells, and mast cells [5,31]. These immune cells are thought to play important roles in parasitic infections, psoriasis induction, tumor progression, dermal inflammation, angiogenesis, wound healing, tissue remodeling, skin sensitization, and tolerance [31,32]. Therefore, regional accumulation in the dermis is necessary for the activities of many drugs that are intended for the prevention and treatment of these local skin diseases. As an important component of the skin associated lymphoid system (SALT), the dendritic cells, as well as their subsets, are suggested to be involved in the initiation and regulation of many immunologic responses. In contrast to the Langerhans cells which mainly induce cellular immunity, the dermal dendritic cells preferentially activate humoral immunity. Novel strategies have been proposed for their use as the targets for the development of both prevention and therapeutic vaccines, as well as for immunological treatment of allergy, tumors and autoimmune diseases [33].
Related Knowledge Centers
- Birbeck Granules
- Epidermis
- Lymph Node
- Oral Mucosa
- Stratum Spinosum
- Dermis
- Macrophage
- Foreskin
- Vaginal Epithelium
- Langerhans Cell Histiocytosis