The marvel of immunity


  Posted by: Dental Design      19th June 2020

Our bodies contain an estimated 30 trillion cells, of which hundreds of billions are recycled each day. These cells coexist with a vast microbiota – the oral cavity alone harbours hundreds of species of bacteria, fungi and viruses. It is estimated that altogether the microorganisms that our bodies play host to outnumber our native cells roughly 2 to 1 (though this varies with the mass of the individual).[i] While we tend to think of ourselves as singular entities, we are essentially giant colonies of microscopic life. Keeping that colony safe from threats is an incredible logistical feat. Given the innumerable threats our immune system deals with constantly, it is remarkably effective.

To accomplish this, the human body has numerous overlapping layers of protection that we generally classify as the innate and the adaptive immune system. The former includes physical and chemical barriers. These not only include the skin­ ­– which helps keep threats out – but also mucous, tears and saliva that clear potentially infectious material, and so forth. Other innate features include the inflammatory response, and the various cells dedicated to signalling, surrounding, destroying and clearing invading microbiota and compromised host cells. All life has features that provide some form of innate protection against outside threats, but adaptive immunity as we commonly understand it evolved in vertebrates around half a billion years ago.[ii]

A key component of our innate immunity is the complement system. This purges the body of foreign pathogens and substances, and also removes dead cells and debris. It does this by tagging foreign bodies with opsonins (thereby attracting phagocytes that devour them), releasing pro-inflammatory mediators, and directly attaching to foreign matter using the membrane attack complex (MAC).[iii] As the name implies, the complement system was classically understood as assisting antibodies. However, we now know that it can sometimes be activated without them.[iv] Inactive precursors to complement are present in blood and other bodily fluids, and activate rapidly in the presence of foreign bacteria – making it one of the fastest acting reactive parts of our immune defences. The MAC response can kill Gram-negative bacteria within minutes without assistance from other immune cells. Gram-positive bacteria are too resilient for MAC, which is why the cascade response escalates to attract phagocytes. This elevated response takes longer to eradicate Gram-positive strains – around 30-60 minutes from detection and marking.[v]

While innate imunity is broadly effective against countless intruders, it is far from foolproof. Some bacteria and viruses have evolved strategies to slip past or overwhelm these defences. Interferons are cytokines that alert the innate immune system to the presence of viruses, recruiting and activating specialised immune cells to contain and combat viral interlopers. Necessarily, most virulent viruses in humans have developed a means to inhibit type 1 interferons in order to prevent detection. Those that can’t achieve this are generally not very pathogenic and can be exploited for vaccination strains.[vi]

Countering these novel strategies is where our adaptive immune system comes into play. The adaptive immune system reacts to novel infections, producing immunoglobulin (antibodies) that bind to pathogens, enabling killer T-cells and the complement system to recognise and attack them.[vii], [viii] This is a more time-consuming process, especially with virgin infections, as the body has to develop a specific T-cell that can target the pathogen. Subsequent attacks by the same pathogen are responded to much more swiftly because memory B-cells effectively keep a record of previous infections, enabling the body to more rapidly produce the appropriate T-cell during successive exposures.[ix], [x] Vaccination programmes take advantage of this by exposing our immune system to inactivated versions of pathogens, which our body can then react to far quicker when encountered ‘in the wild’.

Though the immune system is a remarkable biological accomplishment, it is forever locked in an arms race against invasive bacteria and viruses. Various conditions and medications can affect the immune system, as can age, sleep and stress.[xi], [xii] This is all in addition to the large degree of variation at the individual level in susceptibility and immune response.[xiii]

Where possible, the best defence is to avoid being attacked in the first place. Patients are exposed to countless infections already without adding iatrogenic pathogens to their immune system’s workload. Serious infections including HIV, hepatitis B, hepatitis C and varicella zoster can be transmitted during dental procedures.[xiv]

It is absolutely essential to patient safety to ensure instruments are thoroughly decontaminated and sterilized using reliable equipment. This year marks 20 years since the Lisa sterilizer was launched by leading manufacturer, W&H. Over the last two decades, Lisa has been refined to complete a type B cycle in just 30 minutes and other cycles with a full load in only 13 minutes. With intelligent Eco Dry+ technology that automatically adapts the drying time to the mass of each load, Lisa also enables careful logging of cycle information with fully featured traceability options that provide excellent documentation and security.Furtherstill, the Lara sterilizer offers the fastest sterilization in its class, with regular upgrades available to ensure a future-proof decontamination solution.

While the immune system is an evolutionary marvel, it is by no means perfect. There exist forces that continue to circumvent its defences, which is why it is vital that dental professionals follow robust infection prevention and control protocols to help keep patients safe and healthy.


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[i] Sender R., Fuchs S., Milo R. Revised estimates for the number of human and bacteria cells in the body.  PLoS Biology. 2016; 14(8): e1002533. February 28, 2020.

[ii] Flajnik M. A cold-blooded view of adaptive immunity. Nature Reviews Immunology. 2018; 18: 438-453. February 28, 2020.

[iii] Eriksson O., Mohlin C., Nilsson B., Ekdahi K. The human platelet as an innate immune cell: interactions between activated platelets and the complement system. Frontiers in Immunology. 2019; 10: 1590. February 28, 2020.

[iv] Nesargikar P., Spiller B., Chavez R. The complement system: history, pathways, cascade and inhibitors. European Journal of Microbiology & Immunology. 2012; 2(2): 103-111. February 28, 2020.

[v] Heesterbeek D., Angelier M., Harrison R., Rooijakkers S. Complement and bacterial infections: from molecular mechanisms to therapeutic applications.  Journal of Innate Immunity. 2018; 10: 455-464. February 28, 2020.

[vi] Koyama S., Ishii K., Coban C., Akira S. Innate immune response to viral infection. Cytokines. 2008; 43: 336-341. February 28, 2020.

[vii] Heesterbeek D., Angelier M., Harrison R., Rooijakkers S. Complement and bacterial infections: from molecular mechanisms to therapeutic applications.  Journal of Innate Immunity. 2018; 10: 455-464. February 28, 2020.

[viii] Merle N., Noe R., Halbwachs-Mecarelli L., Fremeaux-Bacchi V., Roumenina L. Complement system part II: role in immunity. Frontiers in Immunology. 2015; 6: e257. February 28, 2020.

[ix] Lu L., Suscovich T., Fortune S., Alter G. Beyond binding: antibody effector functions in infectious diseases. Nature Reviews Immunology. 2017; 18(1): 46-61. February 28, 2020.

[x] McHeyzer-Williams M., Okitsu S., Wang N., McHeyzer-Williams L. Molecular programming of B cell memory. Nature Reviews Immunology. 2012; 12: 24-34. February 28, 2020.

[xi] Minton K. Sleeping off sickness. Nature Reviews Immunology. 2019; 19: 138-139. February 28, 2020.

[xii] Morey J., Boggero I., Scott A., Segerstrom S. Current directions in stress and human immune function.  Current Opinion in Psychology. 2015; 5: 13-17. February 28, 2020.

[xiii] Brodin P., Davis M. Human immune system variation.  Nature Reviews Immunology. 2016; 17(1): 21-29. February 28, 2020.

[xiv] Amirzade-Iranaq M., Khosravi M. Infection control status in dental practice: why to take it serious? International Journal of Medical Reviews. 2017; 4(1): 1-2. February 28, 2020.

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