Langerhans Cell Histiocytosis at a Glance
- A group of rare disorders that are considered reactive but have a broad spectrum of severity.
- The reactive vs. neoplastic nature of the disease is debated. A clonal origin for the cells of Langerhans cell histiocytosis (LCH) in genetically predisposed patients is the most probable hypothesis.
- Histopathologic features consist of a dense infiltrate of histiocytes with a strong epidermotropism. The unifying element is the typical “LCH cell”—a histiocyte with an irregular vesiculated, often reniform nucleus and an abundant, slightly eosinophilic cytoplasm. These cells test are positive for S100 protein, CD1a, and CD207, and contain cytoplasmic Langerhans granules.
- Cutaneous lesions vary from papules to vesicles, pustules, nodules, and ulcers.
- The course of LCH ranges from localized self-healing forms to generalized and fatal cases.
- The most common sites of involvement are the head, trunk, and skin folds.
- Mucosal lesions are usually ulcerated nodules involving mainly gingival and genital regions.
- Associated manifestations include diabetes insipidus and exophthalmos.
- Systemic lesions may affect bones, lungs, bone marrow, liver, spleen, and lymph nodes.
- Aggressive forms may be treated successfully with vinblastine and other drugs.
The term “histiocytoses” identifies a group of diseases that have in common the proliferation of cells of the mononuclear phagocyte system, including dendritic cells.
Histiocytes, formally connective tissue macrophages, and dendritic cells constitute two of the major types of nonlymphoid mononuclear cells and are involved in immune and nonimmune inflammatory responses. Both cells arise in the bone marrow from pluripotential stem cells, but follow different paths of differentiation (Fig. 147-1). The macrophage, detectable by CD68, is a monocyte in the peripheral blood and a macrophage in tissue. It may differentiate into a number of different giant cells, including foreign body, epithelioid, Touton, and Langhans types.
Schematic diagram of the origin of macrophages and dendritic cells. Both macrophages and dendritic cells (antigen presenting cells) are derived from a common bone marrow precursor. In contrast, follicular dendritic cells are thought to be of nonhematopoietic origin. +, most, if not all, cells positive; −, all cells negative, +/−, a minority of cells positive; v, variable intensity. (Adapted from Jaffe R et al: Histiocytic and dendritic cell neoplasms, introduction. In: WHO Classification of Tumors of Haematopoietic and Lympoid Tissues, edited by SH Swerdlow et al. Geneva, Lyon, WHO Press, 2008.)
Dendritic cells are antigen-presenting cells that interact with T cells. The prototype of dendritic cell in the skin is the Langerhans cell (LC). First described by Paul Langerhans in 1868 as a neuronal cell, the LC was first linked to antigen presentation during the 1940s. Precursor cells to the LCs migrate from the dermis into the epidermis where they complete differentiation. LCs have long cytoplasmic projections and a large almost kidney-shaped nucleus. Electron microscopy reveals the characteristic cytoplasmic organelle, the Langerhans or Birbeck granule, a ...