Written by Christina Young and Edited by Mehr Kaur Bawa
Antibodies are secreted proteins that travel in the blood and are a result of an immune system response to a pathogen, such as a bacterium. When an individual is re-infected with the same pathogen, antibodies are quick to bind to them and reactivate the immune system to protect the body [1]. Additionally, in research, antibodies can be used as a label by attaching a fluorescent tag and engineering binding to different proteins of interest, although this is primarily used outside of an organism. The structure of an antibody is typically uniform throughout different organisms, although some species have been shown to utilize “fragmental” forms of antibodies for the same function. Nanobodies, or single-domain antibodies, are found in camel-like species that are 1/10 the size of a conventional antibody and can withstand more changes in the environment [2]. Due to their small size and robust natures, nanobodies are being evaluated for their use as fluorescent markers to track cellular processes in the body.
The field of neurobiology has taken highly to the usage of nanobodies for the fluorescent marking of specific processes and proteins in neurons or nerve cells in the brain. Due to the damage that an immune response can cause to the brain, immune system components are prevented from entry, making it difficult for researchers to track protein activity in that region with conventional antibodies [3]. Since nanobodies are so small and can bypass the immune response block to the brain, they have potential as an alternative to track the movement of proteins between neurons. In 2019, the Dong lab was able to utilize nanobodies in this way to recognize characteristic proteins from neurons to visualize the cellular structures in mice brains [4]. The labels helped identify quantities of specific proteins present in and around the networks formed by the nerve cells. Due to nanobodies’ diminished ability to produce immune responses in other species besides camels, they can be useful in identifying different quantities of proteins and their movement in brain disease progression. More research is needed to determine the effectiveness of nanobodies, as they appear to bind to only particular antigens making some proteins harder to track than others. In addition, they may not bind all of a single type of protein, producing weak visual signals for that protein, and thereby losing valuable information about its activities.
Beyond the brain, nanobodies have been evaluated as a fluorescent label for the central nervous system (CNS), which consists of the spinal cord and brain. Due to the density of the mammalian body, conventional imaging using weaker antibody labels cannot be detected on a live, whole-body animal. Thin layers of tissue have to be cut in order to visualize cell behavior. In 2019, the Cai lab expanded the repertoire of fluorescent labels to create a novel nanobody that provided an easily detectable fluorescence to monitor CNS activity in mice. Their goal was to determine the effects of trauma on the degradation of the CNS and to map healthy nerve tissue, which were readily seen using the nanobody label [5]. These studies open up possibilities for neuroscience and other fields for the production of nanobodies for research in the tracking and tagging of proteins within the body, especially in the case of disease progression in areas that typically prevent immune system entry, such as the brain.
References:
- Bettie J. Graham. “Antibody.” National Human Genome Research Institute. https://www.genome.gov/genetics-glossary/Antibody
- “Discovery of Nanobodies.” Chromtek. 2018. https://www.chromotek.com/technology/discovery-of-nanobodies/
- Thom, G., Hatcher, J., Hearn, A., Paterson, Rodrigo, N., Beljean, A., Gurrell, I., Webster, C. (2017). Isolation of blood-brain barrier-crossing antibodies from a phage display library by competitive elution and their ability to penetrate the central nervous system. mABS. 10: 304-314.
- Dong, J.X., Lee, Y., Kirmiz, M., Palacio, S., Dumitras, C., Moreno, C.M.M., Sando, R., Santana, L.F., Südhof, T.C., Gong, B., Murray, K.D., Trimmer, J.S. (2019) A toolbox of nanobodies developed and validated for use as intrabodies and nanoscale immunolabels in mammalian brain neurons. Neuroscience. 8: 1-25.
- Cai, R., Pan, C., Ghasemigharagoz, A., Todorov, M.I., Förstera, B., Zhao, S., Bhatia. H.S., Parra-Damas, A., Mrowka, L., Theodorou, D., Rempfler, M., Xavier, A.L.R., Kress, B.T., Benakis, C., Steainke, H., Liebscher, S., Bechman, I., Liesz, A., Menze, B., Kerschsteiner, M., Nedergaards, M., Ertürk, A. (2019) Panoptic imaging off transparent mice reveals whole-body neuronal projections and skull-meninges connections. Nature Neuroscience. 22: 317-327.