XB-ART-56898
Front Immunol
2018 Sep 12;9:3128. doi: 10.3389/fimmu.2018.03128.
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Frog Skin Innate Immune Defences: Sensing and Surviving Pathogens.
Varga JFA
,
Bui-Marinos MP
,
Katzenback BA
.
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Amphibian skin is a mucosal surface in direct and continuous contact with a microbially diverse and laden aquatic and/or terrestrial environment. As such, frog skin is an important innate immune organ and first line of defence against pathogens in the environment. Critical to the innate immune functions of frog skin are the maintenance of physical, chemical, cellular, and microbiological barriers and the complex network of interactions that occur across all the barriers. Despite the global decline in amphibian populations, largely as a result of emerging infectious diseases, we understand little regarding the cellular and molecular mechanisms that underlie the innate immune function of amphibian skin and defence against pathogens. In this review, we discuss the structure, cell composition and cellular junctions that contribute to the skin physical barrier, the antimicrobial peptide arsenal that, in part, comprises the chemical barrier, the pattern recognition receptors involved in recognizing pathogens and initiating innate immune responses in the skin, and the contribution of commensal microbes on the skin to pathogen defence. We briefly discuss the influence of environmental abiotic factors (natural and anthropogenic) and pathogens on the immunocompetency of frog skin defences. Although some aspects of frog innate immunity, such as antimicrobial peptides are well-studied; other components and how they contribute to the skin innate immune barrier, are lacking. Elucidating the complex network of interactions occurring at the interface of the frog's external and internal environments will yield insight into the crucial role amphibian skin plays in host defence and the environmental factors leading to compromised barrier integrity, disease, and host mortality.
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Species referenced: Xenopus
Genes referenced: egfr glp1r levi magainins pgla stat3 tlr5 xt6l
GO keywords: innate immune response
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Figure 1. The physical, chemical, cellular, and microbiological innate immune barriers of frog skin. Frog skin, which is mucosal in nature, contains physical, chemical, cellular, and microbiological barriers that work together in defence against pathogen assault. Frog skin is composed of an epidermal and dermal layer, containing resident immune cells throughout the layers. The epidermis is comprised of stratified squamous epithelial cells in three distinct layers: the stratum corneum (1), stratum spinosum (2), and stratum germinativum. The dermis is largely comprised of connective tissue formed by collagenous fibres (black lines) in two layers, the spongious dermis (4) and the compact dermis (6), connected by collagenous columns (white star). In mainly terrestrial frogs, the Eberth-Kastschenko layer (5, thick blue line) separates the spongious dermal layer and compact dermal layer. Glands within the dermal layer include granular glands (a), mucosal glands (b), and small mixed glands (c) that secrete a slew of compounds, including mucus and antimicrobial peptides. Commensal bacteria overlay the frog skin layers, forming the microbiological barrier. The image was, in part, created with the aid of BioRender. |
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