tonofilaments
Summary
Tonofilaments are intermediate filaments composed of cytokeratin found in epithelial cells, especially keratinocytes. They insert into desmosomes and hemidesmosomes, providing mechanical strength to epithelia.
Detail
Tonofilaments are bundles of keratin intermediate filaments (8-10 nm) that anchor to dense plaques of desmosomes (cell-cell) and hemidesmosomes (cell-basement membrane). They are a defining ultrastructural feature of squamous epithelium and squamous cell carcinoma on electron microscopy, helping pathologists distinguish SCC from adenocarcinoma. In pemphigus vulgaris, autoantibodies against desmoglein-3 disrupt desmosome-tonofilament linkage, causing acantholysis. Mallory-Denk bodies in alcoholic hepatitis are damaged, ubiquitinated cytokeratin (8/18) intermediate filaments. Boards keyword: 'tonofilaments + desmosomes on EM' = squamous origin.
Sources
- First Aid for USMLE Step 1 2024
- Robbins Basic Pathology 10th ed
- Junqueira's Basic Histology
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