By Yianna Zhang and Staff Writers, December 2021
When Mariah Carey suggested that a hero lies within all of us, she wasn't wrong.
For many of us, when we step into the spring breeze and take a breath of fresh air, the hero begins to manifest itself. A sniffle here, accompanied by a couple of sneezes there. It's irksome, but it's a critical sign that the hero - our immune system - is safeguarding us against infections and diseases.
WHAT IS THE IMMUNE SYSTEM, REALLY?
The immune system is an extensive network of cells, tissues and organs, like an army of soldiers guarding its territory against incoming enemies. The system's goal, being the army leader, is to protect our bodies against potential threats from entry.
These threats can be disease-causing organisms (pathogens), such as bacteria, viruses and parasites. They can also be foreign substances such as toxins. Collectively, anything that our bodies don't recognise as being part of ourselves can be a threat, which we also call antigens.
Under their competent leadership, we barely notice when our immune systems function smoothly. But without its governance and protection, a simple intrusion from pathogens - as small as an insect bite - could rapidly escalate to severe illnesses.
Because of the broad spectrum of foreign organisms that could invade our bodies, our immune system employs two teams with separate strategies to tackle different threats: The innate immune system and the adaptive immune system.
The innate immune system acts quickly as the first line of defence towards all kinds of antigens. However, when the innate system fails to work, it passes its baton to the adaptive immune system. The adaptive immune system has a unique set of tools to deal with each invader but is more effective towards those they've previously encountered.
DEFENCE ON THE FRONTLINE
The innate immune system makes for a team of very reliable security guards. They are always on duty and prepared to stop invaders that the body does not recognise as being a part of us. But how does one perform such a seemingly herculean role?
Here, two layers of protection are in place: the physical barriers and a group of specialised cells. The physical barriers act as walls to try and block invaders from attacking our bodies. Think our skin, our tears and saliva, or the stomach's highly acidic environment that digests our food and even vaginal discharge. Many of these barriers also have existing communities of healthy microbes that keep the harmful ones at bay.
But these barriers are often not enough. We also need cells - the soldiers that actively identify invaders and send messages to alarm others for support. Our bodies produce millions of specialised cells that move around in our blood. Most of these cells are red blood cells that deliver oxygen to different parts of us. But the immune system relies on a small proportion of white blood cells, which are constantly patrolling for suspicious signs of antigens.
These white blood cells are also known as immune cells or leukocytes. Like all blood cells, they originate from the bone marrow, the sponge-like tissues that make up the hollow part of our long bones. These leukocytes migrate into the blood, as well as other tissues lining our organs, such as the skin and gut. They are highly vigilant at all times so that when antigens are found, they can rapidly produce chemical signals for our body to defend. Complementing the leukocytes are several other compounds within the blood, which can attach to foreign substances and kill them.
Remember the annoying swelling and redness that escorts all sorts of bug bites? Or the fever that irks around with a flu? That's your innate immune system responding to the alarm rung by immune cells by triggering what we call inflammation. These signs - such as swelling, pain, and redness - is our way of trying to repel foreign invasion. Inflammation can also trigger a fever, which raises our body temperature to make certain pathogens as uncomfortable as it makes us.
THE SPECIALIST DOCTORS
The innate immune system is skilled enough to handle most intrusions. But they don't always work, so they sometimes call for experts in the house. Unlike the broad, general attempt to wipe out foreigners by the innate system, the adaptive immune system develops strategic responses for each antigen.
The soldiers of this army - the adaptive immune cells - are not as good as the innate immune cells at eliminating substances they've never encountered. After all, they won't know what specific weapon to use if they cannot identify who they are dealing with. But each of these immune cells is coated in receptors, which are like unique keys that allow them to recognise specific substances. And like us, they have a memory.
This means that once they are familiar with a specific antigen, they can recognise specific patterns on their surfaces and destroy them very effectively. They do this by releasing antibodies, which are little messengers that latch onto foreign particles, and send messages to other cells that the antigen should be destroyed.
Remember our soldiers, the white blood cells? There are two Top Bosses on this team: the T and B cells. Some T cells work with B cells to produce antibodies to neutralise the pathogen. Other T cells can directly kill cells that have been infected with the pathogen.
But it can take up to several days to call upon the T and B cells. Whilst both T and B cells are made in the bone marrow; they are matured in different parts of our body before they can patrol for invaders. During this process, the body makes sure to educate them on how to respond effectively when facing particular invaders, such as to remove the cells that are not responsive enough and to make new cells that work.
But once the adaptive immune system has been 'primed' with a memory of the invader, a specific pool of T and B cells are made so that the next time they encounter the same pathogen, they can come out with a faster and stronger response. This is why vaccines are so effective - because we artificially introduce a part of or an inactive form of the pathogen into the body to produce the relevant memory cells.
ALLERGIES: WHEN NOBODY IS PERFECT
Wait. So, if our immune system is so good at recognising and memorising what's harmful to our bodies, why do some of us have allergies to specific things and others don't?
That's because many of us suffer from hypersensitivity. And not because we cry excessively when watching the Notebook.
Hypersensitivity disorders, or allergies, occur where our adaptive immune system forms memory cells for specific antigens when they shouldn't. This happens when they erroneously identify substances, like pollen and certain food proteins, as being harmful.
As a result, our immune system tries to mediate a response that damages our bodies through the production of chemical signals, antibodies, and inflammation, even without the presence of pathogens. Some people respond severely to some antigens, and they experience anaphylaxis - a severe and life-threatening form of an allergic response.
Currently, allergic diseases affect more than four million Australians and continue to rise in prevalence.
Allergies can be debilitating to the quality of the lives of those living with them, which makes it extremely important to empower Australians with the knowledge of allergies to further their acceptance and understanding of them.
'Meet your Immune System' is part of a series of insights where we will introduce the main types of allergies, how they occur, and what we understand about how to deal with them.
After all, if our immune system is trying to tell us anything - it is that your body is a temple.
Stay tuned. More to come.
This insight was contributed by Yianna Zhang and staff writers. We thank their efforts, creativity and care in bringing these insights to helping Australians with allergies live a safer and happier allergy life. The information on this insight has been credibly sourced. If you'd like to learn more, please get in touch with us.
The information provided on Allergy Life Australia is to generally educate and inform you about living with allergies, intolerances and conditions, and is not intended as medical instruction or as a substitute for diagnosis, examination and advice by a qualified health care provider.