Langerhans cells are specialized immune cells that play a significant part in the body’s defense system. They act as sentinels, constantly surveying their environment. Their distinct functions allow them to bridge different aspects of immunity, contributing to overall health and protection.
Location and Cellular Identity
Langerhans cells are predominantly found in the epidermis, the outermost layer of the skin, where they make up about 1-2% of the total epidermal cell population. They are also present in other stratified squamous epithelia, such as the oral cavity, esophagus, and vagina. These cells reside in the suprabasal layer of these tissues.
As a specialized dendritic cell, Langerhans cells possess long, branching projections that extend throughout the surrounding tissue, allowing them to survey a wide area. A distinguishing feature of Langerhans cells is the presence of Birbeck granules within their cytoplasm. These cells originate from hematopoietic stem cells in the bone marrow and migrate to their resident locations.
Key Role in Immune Surveillance
Langerhans cells function as “first responders” in the skin and other barrier tissues, constantly monitoring for potential threats. They efficiently capture and process antigens, which can include components from pathogens, allergens, or damaged host cells. Upon encountering such antigens, Langerhans cells undergo maturation and internalize the foreign material.
Following antigen capture, Langerhans cells express molecules necessary for T cell activation. They then migrate from the skin through lymphatic vessels to the draining lymph nodes. This migration allows them to present processed antigens to naive T cells, initiating a specific adaptive immune response. This process connects the innate immune system, which provides immediate, non-specific defense, with the adaptive immune system, which develops targeted, long-lasting immunity.
Langerhans Cells in Skin Immunity
Within the skin, Langerhans cells are involved in various immune responses, including defense against infections. They capture microbial antigens, helping to mount a defense against bacteria, viruses, and fungi that breach the skin barrier. Their function is also significant in allergic contact dermatitis, a type of skin allergy. Langerhans cells have been shown to be involved in the activation of T cells in such reactions.
Environmental stressors, such as ultraviolet (UV) radiation, can affect Langerhans cell function. UV exposure can alter their morphology, reduce their numbers in the epidermis, and impair their ability to present antigens. This can contribute to UV-induced immunosuppression. Beyond immediate threats, Langerhans cells also contribute to immune tolerance, preventing the immune system from overreacting to harmless substances. Dysregulation of Langerhans cells is observed in various skin diseases, including autoimmune and inflammatory conditions like psoriasis and atopic dermatitis.