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(cell and molecular biology)
Any of the fibrils converging on desmosomes in epithelial cells.



a filamentous formation in the epithelial cells of animals. While tonofibrils were previously thought to extend from one cell to another, electron-microscope investigations have disproved the notion that such formations are continuous. It has been shown that they converge in the region of the desmosomes, where they bend and reenter the core of the cell. The usual diameter of a tonofibril is approximately 60 angstroms. It is likely that tonofibrils ensure the mechanical stability of cells.

References in periodicals archive ?
We believe that the positive expression of tumor cells for CK and other epithelial markers and the presence of tonofibrils and desmosomes are proportional to the degree of differentiation of squamous cell component existing in this neoplasm.
The histology (presence of glandular components in most cases), immunohistochemistry (variable expression for CK, endomysial antibody, and CEA), and EM data (rare tonofibrils, poorly formed desmosomes) as seen in our case and being reported in the literature confirmed the original belief that GCC is a poorly differentiated adenosquamous carcinoma.