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Electron microscopy is a set of techniques that have seen a lot of use of the last couple of decades as they can image very small structures, such as biological materials and nanomaterials. However, despite their recent interest, they have been used for many decades, long before it was economically feasible to use them regularly. One area where electron microscopy has seen a lot of use is investigating how different allergic reactions occur.
What is Electron Microscopy?
Electron microscopy is a set of high-powered microscopy techniques that use electrons to image a sample rather than photons of light.
There are three main types that are commonly used, which are scanning electron microscopy (SEM), transmission electron microscopy (TEM) and reflection electron microscopy (REM).
They are commonly used in conjunction with each other to provide insights into how the sample behaves. Electron microscopes typically fire electrons towards a sample and how the electrons interact with the sample (through backscattering, transmitting or releasing secondary Auger electrons depending on the type of microscope) is used to not only build up a picture of the sample but to understand the properties the sample has in certain environments/scenarios. This can be used to distinguish different mechanisms/processes.
Electron Microscopy and our Understanding of Allergic Reactions
Despite the growing use in recent years to image materials, electron microscopy techniques have been in use for many decades to image and understand how allergic reactions happen.
There are many different types of allergic reactions that can occur due to several different stimuli and each one must be understood individually. Regardless of the specific area, electron microscopy has been a useful tool over the years for broadening our understanding of allergic reactions.
Some of the earliest research in this area dates back to the 1960s. One example of this is a piece of research from 1963, which investigated the hypersensitivity reaction known as allergic hepatic necrosis that causes liver dysfunction and liver damage. This severe condition is reversible if treated immediately.
Researchers were able to use an electron microscope to investigate what happens to the liver tissue during these necrotic process by visualizing how ferritin localized and formed complexes within the tissue. This approach enabled the researchers to understand that the necrosis of the liver tissue was due to anoxic damage caused by immune thrombi within the sinusoids of the liver.
There have also been several studies performed on the nasal mucosa, i.e., the mucus lining within the nose, and how allergic reactions affect this lining by using electron microscopy. Research conducted in 1975 determined that allergic reactions only have a minimal direct influence on the mucus membrane when allergens are inhaled through the nose. In comparison, they found that flagellated bacteria directly adhered to the mucus membrane and altered the layer significantly.
In 1985, research looked at how acute and chronic allergens changed the morphology and characteristics of nasal mucosa. It also looked at how endonasal polyps and disturbances of the autonomic nervous system presented themselves in allergic patients.
In 2001, electron microscopy was used to investigate pollen, which is one of the most common allergenic particles. The research examined the different particles from six different grass species to investigate how the submicron particles released by the pollen can cause respiratory issues such as asthma attacks.
It was found that the allergen-containing particles within the Poaceae species of plants expelled their cytoplasmic material upon hydration, causing an allergic reaction to occur. The research showcased that the pollen entering the nasal passage diffuses and expels their cytoplasm rapidly across the mucus layer, causing an allergic reaction to occur. It was also found that because the pollen particles release allergen-bearing subatomic particles upon bursting, they can penetrate deeper into the airways of the lungs, inducing symptoms that are similar to bronchial asthma.
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The Future of Electron Microscopy in Researching Allergic Reactions
The year 2020 is offering new insights into allergic reactions. A research team has been able to identify the molecular structure of an antibody known as IgE and has provided insights into the fundamental mechanisms that govern many allergic reactions.
The use of an electron microscope has determined that the antibody has a very rigid structure, which is contradictory to previous thoughts that it is flexible. The research has also found that the molecular structure possesses many allergen-binding moieties.
The research team investigated the therapeutic antibody undergoing clinical trials based on IgE and were able to understand the structural changes involved when the antibody recognizes and binds to allergens.
While research has been carried out for more than 50 years in this field, it is an area that is continuing to produce results. It is likely electron microscopy will be used for many more years to understand the mechanisms at play in different allergic reactions.
References and Further Reading
“Electron Microscopy of Hypersensitivity Reactions: Allergic Hepatic Necrosis”- Sabesin S. M., American Journal of Pathology, 1963
“Scanning electron microscopy of the human nasal mucosa”- Mygind N., Rhinology, 1975
“Electron microscopy findings in allergic reactions of the nasal mucosa”- Jahnke V. and Theopold H. M., Laryngol. Rhinol. Otol., 1983
“Release of allergen-bearing cytoplasm from hydrated pollen: A mechanism common to a variety of grass (Poaceae) species revealed by electron microscopy”- Grote M. et al, Journal of Allergy and Clinical Immunology, 2001, DOI: 10.1067/mai.2001.116431
Medical Xpress: https://medicalxpress.com/news/2020-02-electron-microscopy-scientists-molecular-trigger.htm