I do believe there is quite a bit of firing power behind your question "Are they afraid of something?" The influence of CD147 cannot be underestimated, as it is expressed in epithelial, endothelial cells, erythrocytes, lymphocytes, platelets, cardiomyctes, neurons, olfactory bulbs, retina, cornea, the list is shocking and exhaustive. You can link just about every COVID-19 symptom to CD147.
Recently, several studies have identified the presence of CD147 in cells affected by SARS-CoV-2 whereby the lack or complete absence of ACE2 points to the presence of another functional receptor. One of these papers was on platelets.
When examining alterations of gene expression in platelets in COVID-19, Manne et al. could not detect any expression of ACE2 mRNA. However, they did find evidence of SARS-CoV-2 N1 protein inside platelets of COVID-19 patients. This led them to state "platelets may take-up SARS-COV-2 mRNA independent of ACE2”
(Bhanu Kanth Manne, et al. Platelet Gene Expression and Function in COVID-19 Patients. Blood blood.2020007214. doi: https://doi.org/10.1182/blood.2020007214).
If only they would look for CD147. CD147 is widely expressed in platelets. CD147 can activate platelets and form receptors on platelets. Activated platelets in turn will increase expression of CD147, and the binding of CD147 to platelets enhances inflammatory cytokine production. (Schmidt R, et al. Extracellular matrix metalloproteinase inducer (CD147) is a novel receptor on platelets, activates platelets, and augments nuclear factor kappaB-dependent inflammation in monocytes. Circ Res. 2008;102(3):302-309. doi:10.1161/CIRCRESAHA.107.157990)
The problem with SARS-CoV-2 using CD147 as functional receptor is this immunoglobulin transmembrane glycoprotein is found exerting its influence in areas you don't want it to be found, such as the brain.
I wrote a short commentary on the neurological damage that could be the result of CD147 spike protein binding on Medium. Have a read if you like. https://medium.com/@dorisloh_44829/will-covid-19-infection-result-in-increased-multiple-sclerosis-e2a97306e6da
For an in-depth exploration of CD147 spike protein binding in COVID-19, please read my peer-reviewed paper:
https://www.melatonin-research.net/index.php/MR/article/view/86/568
CD147, the elephant in the room no one wants to see or touch. Is it that scary?
