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The endothelium is a membrane made of cells that primarily lines the inside of the heart and blood vessels. Not only does the membrane fill space, it also participates in a complex bio-signaling that scientists are only beginning to understand. Infections that disrupt the endothelium can cause a variety of disruptions to the healthy function of the body.
The Endothelium
The endothelium was first described in 1865. A layer of cells in the middle of an embryo forms the endothelium and eventually lines all the blood and lymph system vessels. It creates the blood-brain barrier as well as more permeable structures in the lungs, kidneys, lymph nodes and liver. Finally, it lines the heart as the endocardium. The endothelium’s surface is equivalent to the area of a football field, but it only weighs two or three pounds.
When the endothelium was first discovered, scientists believed the cells were nothing more than structural walls. It wasn’t until the 1970s that researchers found out how active the endothelium is in bodily functions. Now, in the twenty-first century, we know that the endothelium’s activities include:
- Filtering fluid in the kidneys, lymph nodes and liver
- Preventing pathogens and toxins from reaching the brain
- Regulating the passage of antigens and microbes through the gut-vascular barrier
- Regulating blood pressure, fluid levels, immune function and glucose & insulin access to other cells
The endothelium responds to specific local needs of the body and its environment. For example, when the body moves from sitting to standing, the endothelium regulates blood pressure to maintain proper blood and oxygen levels throughout the body.
In the 1980s, researchers discovered the endothelium’s diverse genetic expression across different parts of the body that control localized responses. The endothelium is part of a bio-signaling conversation that involves the entire body. This makes it difficult to study in a laboratory. Examining one part of the system does not capture the whole conversation.
Active Infection and the Endothelium
An infectious pathogen can disrupt the endothelium’s complex communication system and cause a wide variety of issues. Vector-borne pathogens, including Bartonella and Borrelia species, and coronaviruses, the cause of COVID-19, can infect the endothelium.
A Bartonella infection can stimulate endothelial cell division by secreting growth-promoting proteins. They can promote production of endothelial growth factor (VEGF), a signaling protein that prompts the growth of blood vessels. More needs to be understood about how infections may be associated with cancer through VEGF and other mechanisms.
Find out more about bacillary angiomatosis and bacillary peliosis, two endothelium growth disruptions caused by Bartonella spp. Galaxy Diagnostics offers tissue PCR testing that can confirm Bartonellosis as a cause of these conditions.
It is important to consider Bartonella spp infection when dealing with endocarditis, swelling of the lining of the heart. A variety of infections can cause endocarditis, but they are usually detected in blood samples. Due to its elusive nature, Bartonella is the most common cause of culture-negative infective endocarditis, defined as infective endocarditis for which a cause is not readily apparent because the pathogen can’t be located.
Borrelia burgdorferi, the bacteria that causes Lyme disease, can also infect the heart and cause a variety of disruptions.
Read about how Bartonella and Borrelia infections affect the heart.
When Borrelia burgdorferi infects the endothelium, it affects immune function signaling. There is growing awareness of the importance of the endothelium’s immune response. When B. burgdorferi or other pathogens infect the endothelium, they change immune system signals. The body’s counter signal responses can set off changes that cause disease symptoms.
Learn more about the host response in chronic illness.
To learn more about pathogenic effects on the endothelium, we look to SARS-CoV-2. Researchers associate a disrupted inflammatory response involving the endothelium with severe COVID-19 cases. Researchers noted the endothelium’s ability to repair itself as a marker for severe COVID-19 recovery.
Post-infection Syndromes and Endothelium Dysfunction
Vector-borne pathogens and pathogens such as SARS-COV-2 are known for post-infection syndromes. While age is a factor in endothelial dysfunction, Long COVID researchers have found long-term changes to the endothelium in patients. Patients with myalgic encephalomyelitis (ME), formerly known as chronic fatigue syndrome, are more likely to have endothelium dysfunction.
Conclusion
Pathogenic effects on the endothelium should continue to be a focal point as we expand our knowledge of this complex system. The health of the endothelium is a determining factor in the body’s ability to recover and successfully communicate across a football field.
Minor updates February 27, 2024
Resources
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Thomas, H. (2016). Gut endothelial cells – Another line of defence. Nature Reviews Gastroenterology & Hepatology, 13(4). 10.1038/nrgastro.2015.205 https://www.nature.com/articles/nrgastro.2015.205#:~:text=New%20findings%20published%20in%20Science,the%20intestine%20into%20the%20bloodstream.
Gonzalez Jr., D. G. (2013, November 7). Should my diastolic pressure change when I stand up? TexasHeart.org. https://www.texasheart.org/heart-health/heart-information-center/frequently-asked-patient-questions/should-my-diastolic-pressure-change-when-i-stand-up/#:~:text=When%20a%20person%20stands%20or,nutrients%20as%20well%20as%20oxygen
Kirby, J. E., & Nekorchuk, D. M. (2002). Bartonella-associated endothelial proliferation depends on inhibition of apoptosis. PNAS, 99(7), 4656-4661. 10.1073/pnas.072292699 https://www.pnas.org/content/99/7/4656#:~:text=Bartonella%20are%20unique%20among%20bacterial,many%20organs%20of%20the%20body
McCord, A. M. et al. (2005). Interaction of Bartonella henselae with endothelial cells promotes monocyte/macrophage chemoattractant protein 1 gene expression and protein production and triggers monocyte migration. Infection and Immunity, 73, 5735-5742. 10.1128/IAI.73.9.5735-5743.2005 https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC1231114/
Ruhl, L. et al. (2021, December 10). Endothelial dysfunction contributes to severe COVID-19 in combination with dysregulated lymphocyte responses and cytokine networks. Signal Transduction and Targeted Therapy, 6, 418. https://www.nature.com/articles/s41392-021-00819-6
Gergel, E. I., & Furie, M. B. (2001). Activation of endothelium by Borrelia burgdorferi in vitro enhances transmigration of specific subsets of T lymphocytes. Infection and Immunity, 69, 2190-2197. 10.1128/IAI.69.4.2190-2197.2001 https://journals.asm.org/doi/full/10.1128/IAI.69.4.2190-2197.2001
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