So, what is the immune system?

So, what is the immune system?

The immune system is a complex network of cells, organs and chemicals that work together to protect us from infection. It is as important as the heart that pumps blood around the body and our brains that allow us to somehow be conscious or not.

One of the things that make our immune systems so fascinating is how it exists in many layers. It's not just a single, physical thing. The immune system is an intricate network that exists in many different places throughout your body doing amazing things!

The history of immunology is one of the most complex fields in science, but it's also one that we're learning more and more about every day. 200 years ago, scientists had only just scratched at its surface with their efforts; today we are on our way to understanding how everything works inside your immune system!

It's probably fair to say that the immune system is just as important to our bodies as our brains, and it is just as complex as our brain!

One of the reasons why it is a challenging science to study the immune system, is because its complexity and abundance make up for so many different components. It can be hard to understand all these various layers working together in perfect harmony- but that doesn't mean there isn't hope!

Recently, a breakthrough in understanding the more ancient part of our immune system could change how we fight future pandemics and for immunologists as well. 

“We’ve learned much more about the host immune response to SARS-CoV-2 in a matter of a few months than we have about many, many other viruses that we’ve dealt with for decades,” says Bali Pulendran at Stanford University in California.

The virus has confounded expectations at every turn, from why it leaves some people unscathed but kills others in days to the “cytokine storms” that wrack the bodies of those who become seriously ill.

Cytokines are small proteins that affect the growth and activity of other immune system cells, as well as blood cells. When they're released into circulation, they signal our bodies to do what is necessary for a healthy defence - but too much can be harmful.

A cytokine storm is the result of an overabundance of cytokines and can be severe or even life-threatening - as it leads to multiple organ failure. But one discovery above all may see immunologists rewriting their textbooks and it concerns the part of the immune system often overlooked called innate immunity. 

Once seen as an unimpressive and primitive bit of human biology, it now turns out to play a pivotal role in how the body reacts from SARS-CoV 2.

The idea of having a better appreciation for what we have is not just recommended, but it may help us see off the next pandemic.

Being vertebrates, us humans are the proud owners of two immune systems. One is our "adaptive" system that helps us fight off infections and other potential threats with precision weapons like antibodies and T-cells alike; this has been an area researchers have paid close attention to during the pandemic.

It is often what people mean when they talk about “the” immune system. 

The other is the innate immune system, which is much less sophisticated, but it also has a huge advantage. Innate immunity consists of fast-acting defences that bludgeon enemies indiscriminately while the ‘special forces’ get ready for their assault.

Our adaptive system is slower to react than innate innate one, taking around several days to become active, leaving the innate system to become a ‘first responder’, as the innate system becomes active immediately.

Innate immunity, however, has long been looked at as uninteresting and primitive as it was assumed to lack memory function and this has been a key factor in distinguishing the two systems.

Adaptive immunity is the key to our immune system's survival. It can remember invaders for years or even decades and respond with a vengeance at any time, if needed. This is known as ‘immune memory’ and is a defining feature of adaptive immunity.

A single exposure to some viruses, such as measles, confers lifelong resistance and is also why vaccines work. Recently though, scientists have come to see our “first responder” innate immune system in a new light. Without it, the “higher” adaptive system would simply be a useless embellishment. 

It turns out that the innate immune system does have a memory. It can remember - for years - what happened after an encounter with a pathogen, so we are more resistant to future infections.

The potential to develop a “life-saving weapon” against the next pandemic is now being explored by scientists, due to this ‘trained immunity’.

“Innate immunity was considered the little brother, not that important,” says Mihai Netea at Radboud University in the Netherlands, who pioneered the rethink. “Now we understand how important it is.”

It now seems possible that stimulating our innate immune systems elicits a form of immune protection that is independent from adaptive memory meaning that vaccines such as measles, oral polio and the Bacillus Calmette-Guérin (BCG) vaccine for tuberculosis could actually confer broad protection against other unrelated pathogens via our immune system.

This suggests that these vaccines can also be seen as a general immune booster, even though they were tailored for specific diseases. This evidence in turn coined a phrase that could lead to a new branch of medicine - “trained immunity”.

When Covid-19 came along immunologists in the early stages of the pandemic were keen to understand what tricks this SARS virus uses in order to evade our immune defences. All disease-causing viruses do so; if they don't, our immune system simply kills them off.

Viruses evolve to fight and block many aspects of our defence and with SARS-CoV-2’s its trick turned out to be evasion of the innate immune response, specifically a group of proteins called interferons. These are released inside a cell when it senses the presence of foreign RNA  and can act as a trusted early warning sign for viral attack.”

“The adaptive immune response depends on the innate immune response to get started,” says Shane Crotty at the La Jolla Institute for Immunology in California. “So if the alarm bells of the innate response are delayed, that is likely to result in a delay of the adaptive immune response.” 

With the interferon response in shambles and adaptive immune system missing, SARS-CoV 2 can wreak havoc without being held back. That’s what has been observed in the most severe covid patients: the virus replicates and spreads rapidly throughout the lungs. Without aid from the adaptive system, the innate system works tirelessly to fill in the gap, which could lead to a cytokine storm that may ensue leading to death.

The virus is not tricksy enough to fool all of those who come in contact with it. Early battles may be lost, but eventually most will mount a strong enough immune response to win the war. 

However, a significant minority still fail to catch up. This is possibly due to them having innate weaknesses that make them more susceptible than others. That leads to trouble because you’re not controlling the viral loads, if that’s the case because the antibody and T-cell responses may come up, but it may be too late.

The fact that this virus can take hold and cause problems even after an infection has suggested trained immunity is something worthy and beneficial to pursue - for survival. 

Older Post Newer Post