Langerhans Cells: Skin Immune Cells Explained

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

Langerhans cells are a specialized population of dendritic cells that reside in the epidermis, where they act as the skin's frontline antigen-presenting cells. They are identified histologically by rod-shaped or racket-shaped Birbeck granules on electron microscopy and by expression of langerin (CD207), a C-type lectin receptor, with CD1a also used as a marker in humans.

Understanding Langerhans cells matters because they sit at the interface between the body and the outside world. Every scratch, insect bite, allergen contact, and vaccine injection passes through or near the epidermis, and Langerhans cells are among the first immune cells to sample those events. They decide whether the immune system should attack or tolerate what it encounters, and that decision shapes outcomes from contact allergy to vaccine response to tumor surveillance. In veterinary medicine, the same biology helps explain why some skin diseases behave the way they do in dogs, cats, and horses, and why cutaneous histiocytomas are a common clinical puzzle.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

What Are Langerhans Cells?

Langerhans cells (often abbreviated LC) are a subset of dendritic cells. Dendritic cells are professional antigen-presenting cells, meaning their main job is to capture antigens, process them into peptide fragments, and display those fragments on major histocompatibility complex (MHC) molecules so that T lymphocytes can recognize them. The term "professional" distinguishes them from other cells that can present antigen but do so less efficiently.

Langerhans cells occupy a specific anatomical niche: the suprabasal layers of the epidermis, just below the stratum corneum. In humans they form a network that covers nearly the entire skin surface. In mice, the epidermis harbors two key resident immune populations, dendritic epidermal T cells (DETCs, a subset of invariant gamma-delta T cells) and Langerhans cells, both of which contribute to immune surveillance, barrier integrity, and tissue homeostasis [1].

A useful way to think about Langerhans cells is as resident tissue macrophages with antigen-presenting capability. They arise from embryonic precursors that seed the skin before birth and maintain themselves locally under steady-state conditions. During inflammation, circulating monocytes can be recruited into the epidermis and differentiate into monocyte-derived Langerhans-like cells, which may behave differently from the resident population [2].

Why the Name Matters

Paul Langerhans first described these cells in 1868 using gold chloride staining, before anyone knew what they did. For decades they were misidentified as intraepidermal nerve cells. The name stuck even after their immune function was established. Students should not confuse Langerhans cells with the islets of Langerhans in the pancreas, which are unrelated endocrine structures named after the same anatomist.

Key Markers and Identification

Birbeck Granules

Birbeck granules are the ultrastructural hallmark of Langerhans cells. They appear on transmission electron microscopy as rod-shaped organelles with a central striated line and a terminal vesicular expansion, giving them a racket or tennis-racket appearance [3]. These granules are involved in antigen uptake and processing. Their presence on electron microscopy has historically been the gold standard for identifying Langerhans cells in tissue sections.

Langerin (CD207)

Langerin, also known as CD207, is a C-type lectin receptor that is the most widely used immunohistochemical marker for Langerhans cells across species. It is expressed on the cell surface and is also found in Birbeck granule membranes. Because langerin is involved in antigen recognition and internalization, it is both a marker and a functional receptor [4].

CD1a

CD1a is a surface molecule that presents lipid antigens to T cells. In humans, CD1a is a reliable marker for Langerhans cells and is commonly used in diagnostic immunohistochemistry. In veterinary species, CD1a cross-reactivity varies, and langerin is generally preferred for species-specific identification.

Species Differences in Markers

Langerin markers differ across veterinary species. In dogs, langerin (CD207) is expressed on epidermal Langerhans cells and is used in diagnostic panels for cutaneous histiocytic lesions. In cats, langerin expression has been documented on Langerhans cells, though antibody availability and cross-reactivity require validation for each laboratory. In horses, langerin-positive cells have been identified in the epidermis, but the full marker panel for equine Langerhans cells is less standardized than in humans or mice. Students should always confirm which antibody clone and which species a laboratory has validated before interpreting immunohistochemistry results.

Langerhans Cells vs. Dermal Dendritic Cells

The skin contains at least two major dendritic cell populations: Langerhans cells in the epidermis and dermal dendritic cells (DDCs) in the dermis. These are distinct cell types with different origins, markers, and functions.

A genome-wide comparison of human skin migratory CD1a-positive Langerhans cells and CD11c-positive dermal dendritic cells demonstrated significant differences between these cell types, including preferential expression of 625 genes in Langerhans cells and 914 genes in dermal dendritic cells [5]. This molecular signature confirms that they are not interchangeable.

Dermal dendritic cells lack Birbeck granules and do not express langerin. They occupy the dermis, where they encounter antigens that have crossed the epidermal barrier or entered through the dermal vasculature. In a low-inflammatory skin environment, Langerhans cells but not dermal dendritic cells contribute to tolerance induction, which is why Langerhans cells are a target for specific-tolerance therapies [6].

Comparison Table

How Langerhans Cells Work: Step by Step

Step 1: Antigen Capture

Langerhans cells extend dendritic processes between keratinocytes to sample the epidermal environment. They capture antigens through receptors including langerin, which binds carbohydrate structures on pathogens and allergens. The antigen is internalized into endosomes and processed into peptide fragments.

Step 2: Migration to Draining Lymph Nodes

After antigen capture, Langerhans cells downregulate their epidermal adhesion molecules and migrate through the dermis into lymphatic vessels. They travel to the draining lymph node, where they arrive as mature dendritic cells. This migration is essential for initiating adaptive immune responses. Tick bites and tick saliva reprogram human Langerhans cells to increase migration into lymphatic tissues and adopt a tolerogenic state, marked by reduced ability to induce pro-inflammatory helper T cells and enhanced promotion of type 2 and regulatory T cell responses [7].

Step 3: Antigen Presentation to T Cells

In the lymph node, Langerhans cells present processed antigen on MHC class II molecules to CD4-positive helper T cells and on MHC class I molecules to CD8-positive cytotoxic T cells. They also provide costimulatory signals through molecules such as CD80, CD86, and CD40. The balance of these signals determines whether the T cell becomes activated, becomes tolerant, or differentiates into a regulatory subset.

Step 4: Tolerance or Activation

In healthy skin, Langerhans cells can promote tolerance. In normal human skin samples, Langerhans cells with high HLA-II, CD86, and PD-L2 expression directly contacted PD-1-positive tissue-resident memory T cells and CTLA-4-positive regulatory T cells in the epidermis, indicating an axis of peripheral tolerance in a steady state [8]. Environmental insults such as UVB radiation and hapten exposure downregulated HLA-II and CD86 on Langerhans cells, suggesting that disruption of this tolerogenic axis contributes to skin inflammation [8].

This dual capacity to activate or suppress immune responses is why some reviews describe Langerhans cells as "Janus" cells, capable of promoting or suppressing immunity depending on the microenvironment [9].

Histology and Microscopy: What You See

Light Microscopy

On routine hematoxylin and eosin (H&E) stained sections, Langerhans cells are difficult to identify because their cytoplasm is pale and their nuclei blend with surrounding keratinocytes. They are best seen with special stains or immunohistochemistry. In human skin, CD1a immunohistochemistry highlights Langerhans cells as brown, dendritic cells scattered throughout the epidermis.

Electron Microscopy

Transmission electron microscopy (TEM) reveals Birbeck granules as rod-shaped structures with a central striated core and a terminal vesicle [3]. These granules are approximately 0.1 to 0.5 micrometers in length. The presence of Birbeck granules in a cell within the epidermis confirms its identity as a Langerhans cell.

Immunohistochemistry in Veterinary Practice

In dogs, langerin immunohistochemistry is used to distinguish cutaneous histiocytomas from other round cell tumors. Cutaneous histiocytomas are common benign tumors of dogs that arise from Langerhans cell or dermal dendritic cell lineage. They typically present as rapid-growing, hairless nodules on the head, ears, and limbs of young dogs. Most regress spontaneously within weeks to months, but biopsy may be needed to rule out mast cell tumors or other neoplasms.

In cats, cutaneous histiocytic proliferative disorders are less common than in dogs but do occur. Feline progressive histiocytosis and feline pulmonary Langerhans cell histiocytosis are recognized entities. Immunohistochemistry for langerin and CD1a helps classify these lesions.

In horses, equine cutaneous histiocytoma is rare. When histiocytic lesions are identified, langerin staining can help determine whether they are of Langerhans cell origin.

Comparative Immunology: Langerhans Cells Across Species

Dogs

Canine Langerhans cells express langerin and are found in the epidermis. Cutaneous histiocytomas are the most common histiocytic tumor in dogs and are considered a relevant differential for any rapidly growing cutaneous nodule in a young dog. The tumors are typically composed of a mixture of Langerhans cells and dermal dendritic cells, and they usually regress without treatment.

Cats

Feline Langerhans cells have been identified using langerin immunohistochemistry. Feline progressive histiocytosis is a rare disease characterized by multiple cutaneous nodules that may progress to systemic involvement. Feline pulmonary Langerhans cell histiocytosis has also been reported.

Horses

Equine Langerhans cells are present in the epidermis and express langerin. Equine cutaneous histiocytic lesions are uncommon, but when they occur, immunohistochemistry can help classify them.

Mice

Mouse Langerhans cells are a well-studied model system. Postnatal maturation of mouse Langerhans cells proceeds independently of canonical gamma-delta DETCs and is independent of microbial colonization, as shown by analysis of germfree mice and wildlings [1]. Comparative analysis with developing human epidermis reveals partially conserved differentiation programs [1].

Clinical Relevance, Limitations and Common Mistakes

Langerhans Cell Histiocytosis

Langerhans cell histiocytosis (LCH) is a rare disorder characterized by accumulation of cells with morphological and phenotypic resemblance to Langerhans cells [10]. It is most frequent among the histiocytoses, a group of rare disorders characterized by accumulation of cells thought to be derived from dendritic cells or macrophages [11]. LCH is a clonal myeloid disorder driven by activating mutations in the MAPK/ERK signaling cascade in most cases [10]. Clinical presentations range from mild to disseminated and sometimes life-threatening forms [11].

LCH is rare in animals but has been reported in dogs and cats. In dogs, the more common differential is cutaneous histiocytoma, which is typically benign and self-limiting. Distinguishing between these requires histopathology and immunohistochemistry.

Cutaneous Histiocytomas in Dogs

Cutaneous histiocytomas are common in young dogs and usually present as solitary, rapidly growing, hairless nodules. They are benign and typically regress spontaneously within 4 to 12 weeks. Biopsy may be performed to rule out mast cell tumor, which can look similar clinically. Immunohistochemistry for langerin and CD1a helps confirm the diagnosis.

Common Mistakes Students Make

1. Confusing Langerhans cells with dermal dendritic cells. They are different cell types in different locations with different markers.
2. Assuming langerin is a universal marker. Antibody clones and species cross-reactivity vary, so each laboratory must validate its own protocol.
3. Forgetting that Langerhans cells can promote tolerance, not just activation. In steady-state skin, they help maintain peripheral tolerance to harmless antigens.
4. Overlooking species differences. Human markers such as CD1a may not work in dogs, cats, or horses.
5. Confusing Langerhans cells with the islets of Langerhans in the pancreas. They share a name but are unrelated.
6. Assuming that all histiocytic tumors are malignant. Cutaneous histiocytomas in dogs are benign and often regress without treatment.

Limitations

Individual cases require veterinary assessment. Histopathology and immunohistochemistry results must be interpreted in the context of clinical presentation, and treatment decisions should be made by a licensed veterinarian.

Quick Review

1. Langerhans cells are dendritic cells resident in the epidermis.
2. Birbeck granules on electron microscopy and langerin (CD207) expression are the defining features.
3. Dermal dendritic cells lack Birbeck granules and langerin, and occupy the dermis.
4. Langerhans cells migrate to draining lymph nodes to present antigen to T cells.
5. In steady-state skin, Langerhans cells promote tolerance. In inflammation, they promote activation.
6. Species differences in langerin markers exist across dogs, cats, and horses.
7. Cutaneous histiocytomas in dogs are a common benign differential for Langerhans cell lesions.

Frequently Asked Questions

What are Langerhans cells?

Langerhans cells are specialized dendritic cells that reside in the epidermis and act as antigen-presenting cells. They are identified by Birbeck granules on electron microscopy and by langerin (CD207) expression.

How do Langerhans cells differ from dermal dendritic cells?

Langerhans cells live in the epidermis and express langerin and Birbeck granules. Dermal dendritic cells live in the dermis and lack both markers.

What is the function of Langerhans cells?

Langerhans cells capture antigens in the skin, migrate to draining lymph nodes, and present antigen to T cells. They can promote either immune activation or tolerance depending on the context.

Are Langerhans cells found in animals?

Yes. Langerhans cells have been identified in dogs, cats, horses, mice, and other species. Marker expression varies by species, so species-specific antibodies are needed for immunohistochemistry.

What is Langerhans cell histiocytosis?

Langerhans cell histiocytosis is a rare disorder characterized by accumulation of cells resembling Langerhans cells. It is driven by MAPK pathway mutations in most cases and is rare in animals.

What is the difference between Langerhans cells and cutaneous histiocytomas in dogs?

Cutaneous histiocytomas are benign skin tumors in dogs that arise from Langerhans cell or dermal dendritic cell lineage. They are common and usually regress spontaneously, while Langerhans cell histiocytosis is a systemic disorder that is rare in animals.

Related Articles

• Feline Immune-Mediated Skin Disease: Diagnosis and Treatment
• Canine Immune-Mediated Skin Disease: Diagnostic and Management Approach
• Mouse Skin Single Cell Rna Seq
• Single-Cell TCR and BCR Sequencing: Library Preparation Strategies for Immune Repertoire Analysis
• Why Is My Dog having lumps on skin? Lipoma vs Mast Cell vs Cyst Diagnosis
• Computational Immunology: Modeling the Immune System
• 3 Parts of Cell Theory: Explained Simply
• Cell Image Guide: Labeled Diagrams of Cell Structures

Sources

1. Distinct postnatal trajectories of mouse dendritic epidermal T cells and Langerhans cells independent of microbiota.
2. Tolerogenic Monocyte-Derived Langerhans Cells Promote Melanoma Progression and Immunotherapy Resistance through Aryl Hydrocarbon Receptor-Cyclooxygenase-2 Activation.
3. Langerhans Cells (TEM) - Skin
4. Targeting Langerhans cells using a modular mannosylated nucleic acid-based vaccine platform.
5. Distinct molecular signature of human skin Langerhans cells denotes critical differences in cutaneous dendritic cell immune regulation.
6. A low inflammatory, Langerhans cell-targeted microprojection patch to deliver ovalbumin to the epidermis of mouse skin.
7. Human epidermal Langerhans cells induce tolerance and hamper T cell function upon tick-borne pathogen transmission.
8. Langerhans Cells Directly Interact with Resident T Cells in the Human Epidermis.
9. Friend or foe? - Janus Langerhans cells in skin immunity and promising clinical application.
10. A case of mixed histiocytosis (Erdheim-Chester disease and Langerhans cell histiocytosis) with STEAP3-associated anemia and type 4 hemochromatosis.
11. [[Histiocytoses and neoplasms of the macrophage-dendritic cell lineages. Comparison of recent WHO classification published 2017 and classification of Histiocyte Society published 2016].](https://pubmed.ncbi.nlm.nih.gov/33380149/)