Langerhans

Langerhans cells are a specialized subset of dendritic cells resident in the epidermis and mucosal epithelia. They function as antigen-presenting cells that detect pathogens, process antigens, and migrate to nearby lymph nodes to activate T cells, contributing to skin immune surveillance and tolerance. They form a network with keratinocytes and other immune cells in the epidermis.

Named after Paul Langerhans, who described them in 1868, these cells have a characteristic dendritic morphology. Electron microscopy reveals Birbeck granules, tennis-racket–shaped organelles that are pathognomonic for Langerhans cells.

Immunophenotypically, Langerhans cells are CD1a-positive, Langerin (CD207)-positive, and S-100 positive, with expression of MHC class II. They originate from hematopoietic precursors and are maintained in the epidermis through a balance of local proliferation and replenishment from circulating precursors.

Location and function are tied to their role in the immune system. They reside predominantly in the epidermis but are also found in mucosal tissues. They capture microbial antigens, process them, and present peptide fragments to naïve T cells in lymph nodes, thereby initiating adaptive immune responses. They contribute to immune defense against skin pathogens and participate in establishing local tolerance under steady-state conditions.

Clinical relevance: Langerhans cell histiocytosis (LCH) is a rare disorder characterized by clonal proliferation of Langerhans cells, which can cause bone lesions, skin rashes, and involvement of other organs. Diagnosis relies on biopsy demonstrating CD1a and Langerin positivity, often with Birbeck granules on electron microscopy; treatment varies by extent and may include surgery, chemotherapy, or targeted therapy.

Disambiguation: Langerhans is also the historical name for the pancreatic islets of Langerhans, named after the same scientist, though they are distinct structures.