Immunome Research
Open Access

Understanding the Immunology of Skin and Mucous Membranes as Barrier Surfaces

Ewelina Grywalska^{* *}Correspondence: Ewelina Grywalska, Department of Experimental Immunology, Medical University of Lublin, Lublin, Poland, Email:

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About the Study

The human body is continuously exposed to a variety of microorganisms, including bacteria, viruses, fungi, and parasites. To prevent these pathogens from invading the body and causing infections, the immune system employs a complex network of defense mechanisms. Barrier surfaces, such as the skin and mucous membranes, play a crucial role in protecting the body against external threats.

Skin as a barrier surface

The skin is the largest organ of the body and acts as the primary physical barrier against invading pathogens. It consists of two main layers, the epidermis and the dermis, each with specific immunological functions. The epidermis serves as the first line of defense, composed of tightly packed epithelial cells that provide a physical barrier to prevent pathogen entry. Additionally, the epidermis contains specialized immune cells, such as Langerhans cells, which play a vital role in antigen presentation and immune activation.

Beneath the epidermis lies the dermis, a connective tissue layer that houses a diverse array of immune cells, including macrophages, dendritic cells, and mast cells. These cells function in immune surveillance, phagocytosis, and the production of inflammatory mediators. In the event of a breach in the epidermal barrier, these immune cells quickly respond to eliminate invading pathogens and initiate an immune response.

Mucous membranes as barrier surfaces

Mucous membranes line the body's internal cavities, including the respiratory, gastrointestinal, and urogenital tracts. These membranes possess unique structural and immunological features that enable them to defend against pathogens while maintaining normal physiological functions.

The mucosal epithelium is composed of specialized cells that secrete mucus, a viscous substance that acts as a physical barrier, trapping and preventing pathogens from reaching underlying tissues. Mucosal surfaces also contain cilia, which move in coordinated patterns to propel mucus and trapped pathogens out of the body.

Beneath the mucosal epithelium, specialized immune cells called intraepithelial lymphocytes and resident dendritic cells continuously survey the environment for potential threats. These cells express pattern recognition receptors that can recognize conserved microbial components, triggering an immune response. Mucosal-Associated Lymphoid Tissue (MALT), including tonsils, adenoids, and Peyer's patches, is strategically located along mucosal surfaces and houses B and T lymphocytes, which play crucial roles in adaptive immunity.

Mucosal surfaces also possess a unique immune mechanism called secretory IgA (sIgA). sIgA is the predominant antibody class found in mucosal secretions and provides defense against pathogens by neutralization, aggregation, and immune exclusion. Additionally, mucosal surfaces have regulatory T cells that help maintain immune homeostasis, preventing excessive inflammation and immune-mediated damage.

Skin and mucosal immune responses

Although the skin and mucosal surfaces have distinct immunological features, they are interconnected and communicate with each other. Immune cells and soluble factors can travel between these barrier surfaces, coordinating immune responses and providing cross-protection.

For example, dendritic cells can migrate from the skin to regional lymph nodes, where they present antigens to T cells and initiate adaptive immune responses. Likewise, lymphocytes activated in mucosal tissues can recirculate to the skin, contributing to immune surveillance and defense against cutaneous pathogens.

Furthermore, the Gut-Associated Lymphoid Tissue (GALT) interacts with the skin immune system through a process known as the gut-skin axis. The gut microbiota influences systemic immune responses, which can impact skin health and disease. Dysregulation of this axis has been implicated in various skin conditions, such as psoriasis and atopic dermatitis.