SEARCH RESULTS FOR: Langerhans-Cell-Histiocytosis

Langerhans Cell Histiocytosis

Langerhans Cell Histiocytosis: Pathogenesis and clinical findings Precursor cells differentiateàClonal expansion of abnormal (constitutive MAPK activation) CD1a+/CD207+ (Langerhans cell phenotype surface receptors) dendritic cells in tissue(s) Somatic BRAFV600E mutation: BRAF is a kinase in the MAPK pathway Other somatic (non- reproductive cell) mutations Idiopathic (unknown cause) Mutation(s) can occur in one of these precursor cell types* Hematopoietic stem cell (earliest cell of blood cell differentiation) in bone marrow Committed dendritic cell (type of myeloid antigen-presenting cell) precursor in bone marrow or blood Committed dendritic cell precursor in tissue Constitutive activation of the MAPK pathway (signalling pathway that regulates variety of cellular processes) in one of these precursor cell types *Note: Based on the “misguided myeloid differentiation” modelàthe earlier the mutation(s) occur in the myeloid cell differentiation pathway, the more severe the disease. Langerhans Cell Histiocytosis Accumulation of abnormal CD1a+/CD207+ dendritic cells (Langerhans Cell Histiocytosis cells or LCH cells) with an inflammatory background in one or more organs Authors: Ran (Marissa) Zhang Reviewers: Mehul Gupta Kiera Pajunen Yan Yu* Lynn Savoie* * MD at time of publication ↑ recruitment & activation of T cells, macrophages, eosinophils in tissue(s) around the body ↓ CCR7 & CXCR4 (chemokine receptors) expression on LCH cellsàinhibits migration of LCH cells to lymph nodes ↑ BCLXL (an apoptosis regulator protein) expression on LCH cellsà inhibits apoptosis of LCH cells Immune cell infiltration & ↑ pro-inflammatory chemokine/cytokine release à dysregulated local & systemic inflammation Accumulation of LCH cells in tissue(s) around the body Inflammatory lesion (an area of abnormal tissue) formation in one or more organs: In pituitary stalk Mass effectà obstruction of antidiuretic hormone (complex mechanisms) In liver Invasion & accumulation of cells foreign to liverà expands liver Chronic local inflammation Scarring of bile ducts ↓ bilirubin clearance from liveràbuildup into serum ↑ serum bilirubin Jaundice In cortical bone Cytokine production à↑ osteoclast (cells that break down bone) activity ↑ rate of bone loss Osteolytic bone lesions In bone marrow Unclear mechanism but likely due to macrophage activation ↑ phagocytosis (ingestion & destruction) of blood cells In spleen Invasion & accumulation of cells foreign to spleen Forms aggregates that expand the red pulp (functions as the blood filter in spleen) Splenomegaly In skin Unclear mechanisms Variable presentations: most commonly pinpoint erythematous (red) papules or erythematous plaques with crusting & scaling Hepatomegaly • BRAF- B-Raf proto-oncogene, serine/threonine kinase • CCR7- C-C motif chemokine receptor type 7 • CD1a- Cluster of differentiation 1A • CD207- C-type lectin domain family 4 member k • CXCR4- C-X-C chemokine receptor type 4 • LCH- Langerhans Cell Histiocytosis • MAPK- Mitogen-activated protein kinase Diabetes Insipidus Abbreviations: • BCLXL- B-cell lymphoma-extra large Anemia, thrombocytopenia &/or neutropenia Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published January 13, 2022 on www.thecalgaryguide.com