While most COVID-19 patients with loss of smell (anosmia) recover their olfactory senses, some do not. This may be due to an autoimmune-like response against nerve cells of the olfactory epithelium.
A recent study by researchers at Duke, Harvard and the University of California-San Diego analyzed olfactory epithelial samples from 24 biopsies of which 9 had a lasting olfactory loss. Single-cell analyses revealed widespread infiltration of T-cells, especially γδ T cells expressing inflammation-inducing interferon-γ and reduction of anti-inflammatory M2 macrophages in the olfactory epithelium. The inflammation and reduction in the number of olfactory sensory neurons are observed even after the absence of notable SARS-CoV-2 RNA or protein in the tissues.
Studies like these provide insights into potential therapies and management techniques. For example: Since it has been observed that there is a massive infiltration of pro-inflammatory cells in the olfactory epithelium in patients with long-term loss of smell, drugs selectively blocking these cells could be developed.
Phago 'Citations'
John B. Finlay, David H. Brann, Ralph Abi Hachem, David W. Jang, Allison D. Oliva, Tiffany Ko, Rupali Gupta, Sebastian A. Wellford, E. Ashley Moseman, Sophie S. Jang, Carol H. Yan, Hiroaki Matsunami, Tatsuya Tsukahara, Sandeep Robert Datta, Bradley J. Goldstein. Persistent post–COVID-19 smell loss is associated with immune cell infiltration and altered gene expression in olfactory epithelium. Science Translational Medicine, 2022; 14 (676) DOI: 10.1126/scitranslmed.add0484
Duke University Medical Center. (2022, December 21). Scientists find key reason why loss of smell occurs in long COVID-19: The inflammatory mechanism could also help explain other long COVID-19 symptoms. ScienceDaily. Retrieved December 26, 2022 from www.sciencedaily.com/releases/2022/12/221221154434.htm
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