Intermediate filaments.

Intermediate filaments form a class of insoluble cytoplasmic filaments ofdimensions intermediate in size between those of microtubules (about 25 nm in diameter) and microfilaments (about 7 nm in diameter). Thus, they are generally known as intermediate-sized filaments (IF) ' or 10-nm filaments. They have been identified in virtually all differentiated types of cells and it seems possible that IF-like proteins also are present in even the simplest eukaryote cell types. With immunological, biochemical, and molecular biological techniques, it has been possible to distinguish at least five distinct classes of proteins that constitute IF in different cells or tissues (30, 31, 46, 67): desmin or skeletin in myogenic cells; neurofilaments in neuronal cells; glial filaments in astroglia and related cells; vimentin or decamin in mesenchymally derived cells; and a more complex group of keratins or cytokeratins in epithelial tissues.