Skin Immunity

Abstract

Skin is the largest organ of the body with a complex network of multitude of cell types that perform plastic and dynamic cellular communication to maintain several vital processes such as inflammation, immune response including induction of tolerance and disease prevention, wound healing, and angiogenesis. Of paramount importance are immunological functions of the skin that protect from harmful exposure coming from external and internal environments. Awareness of skin immunity can provide a better comprehension of inflammation, autoimmunity, cancer, graft-versus-host disease, vaccination, and immunotherapy approaches. This paper will update on what we currently know about immune sentinels contributing to skin immunity.

The Brain–Skin Connection and the Pathogenesis of Psoriasis: A Review with a Focus on the Serotonergic System

“…A recent paper reviewed the use of murine models to understand skin immunity, especially at the level of psoriasis, and stresses the main similarities and differences with human skin [22]. The skin immune system is composed of resident and recruited innate immune system (IIS) and adaptive immune system (AIS) cells that are activated by epidermal structures, microorganisms and other stimuli, and that crosstalk with skin cells, mainly KCs, in order to repair the skin barrier [23,24]. The initiation of immune responses in the skin is due to signals of the IIS, while the cells and signaling molecules of the AIS prolong inflammation [25].…”

“…The cells involved in skin immunity have different skin locations ( Figure 1). In the epidermis, coexisting with KCs and melanocytes, there are LCs, which are dendritic cells (DCs) of the IIS, and the only antigen-presenting cells (APC) present in healthy epidermis, which highlights their role as first line fighters [24,27]. Additionally, CD8+ resident memory T cells of the AIS can also be found in the epidermis.…”

“…The initiation of the skin immune response occurs when the skin barrier is broken (by wounds or through tight junctions in the skin appendages that lack the SC). Cutaneous LCs are attracted to the epidermis in a chemotactic process induced by chemokines produced by KCs [24,27] and are able to elongate their dendrites outward beyond the tight junctions to uptake external antigens [16]. Keratinocytes act not only as a physical barrier in the epidermis, but also have sensors that recognize foreign or microbial agents and tissue damage, through pattern recognition receptors which, upon stimulation, lead to the production of secondary mediators, such as antimicrobial peptides (AMPs) and pro-inflammatory chemokines and cytokines.…”

“…Upon stimulation, pDCs differentiate into DCs and/or may activate myeloid DCs (mDCs) in an IFN-α-dependent manner [31,32]. Dermal MCs also function in the activation and recruitment of immune-competent cells, being able, for example, to activate KCs and communicate with other cells [24]. Additionally, they can behave like APCs, interact with other (professional) APCs, (e.g., LCs and DCs) via TNF-α and histamine, which is essential for these to migrate, maturate and present the antigen [33].…”

The Effectiveness of P53 Polymorphism in Susceptibility to Human Papillomavirus and Molluscum contagiosum Infections

“…The main functions of the skin are the Protection and defense against several stimuli and main function of the skin barrier is the protection from entry of microorganisms 10 . Skin composed of two structural compartments: the epidermis and the dermis which composed of several functionally different cells 11 . Stratum corneum cells (Keratinocytes) produce Filaggrin binding to Keratin fibers to form a protective tight barrier which prevents the entry of different pathogens 12 , the impair of skin barrier cause several infection mostly caused by Herpis virus, Human Papillomavirus and Molluscum contagiosum virus 13 .…”