Neurofilament light polypeptide, also known as neurofilament light chain, abbreviated to NF-L or Nfl and with the HGNC name NEFL is a member of the intermediate filament protein family. This protein family consists of over 50 human proteins divided into 5 major classes, the Class I and II keratins, Class III vimentin, GFAP, desmin and the others, the Class IV neurofilaments and the Class V nuclear lamins. There are four major neurofilament subunits, NF-L, NF-M, NF-H and α-internexin. These form heteropolymers which assemble to produce 10nm neurofilaments which are only expressed in neurons where they are major structural proteins, particularly concentrated in large projection axons. Axons are particularly sensitive to mechanical and metabolic compromise and as a result axonal degeneration is a significant problem in many neurological disorders. The detection of neurofilament subunits in CSF and blood has therefore become widely used as a biomarker of ongoing axonal compromise. The NF-L protein is encoded by the NEFLgene.[5][6] Neurofilament light chain is a biomarker that can be measured with immunoassays in cerebrospinal fluid and plasma and reflects axonal damage in a wide variety of neurological disorders.[7][8] It is a useful marker for disease monitoring in amyotrophic lateral sclerosis,[9]multiple sclerosis,[10]Alzheimer's disease,[11][12] and more recently Huntington's disease.[13] It is also promising marker for follow-up of patients with brain tumors.[14] Higher levels of blood or CSF NF-L have been associated with increased mortality, as would be expected as release of this protein reflects ongoing axonal loss.[15] Recent work performed as a collaboration between EnCor Biotechnology Inc. and the University of Florida showed that the NF-L antibodies employed in the most widely used NF-L assays are specific for cleaved forms of NF-L generated by proteolysis induced by cell death.[16] Methods used in different studies for NfL measurement are sandwich enzyme-linked immunosorbent assay (ELISA), electrochemiluminescence, and high-sensitive single molecule array (SIMOA).[17]
Rat brain cells grown in tissue culture and stained, in green, with an antibody to neurofilament subunit NF-L, which reveals a large neuron. The culture was stained in red for α-internexin, which in this culture is found in neuronal stem cells surrounding the large neuron. Image courtesy of EnCor Biotechnology Inc.A formalin fixed and paraffin embedded section of human cerebellum stained with an antibody to NF-L revealed with a brown dye, cell nuclei are revealed with a blue dye. Nuclear rich region at left is granular layer, region at right is molecular layer. The antibody binds processes of basket cells, parallel fiber axons, the perikarya of Purkinje cells and various othe axons. Image courtesy of EnCor Biotechnology Inc.
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