Every day we’re exposed to millions of microscopic germs – bacteria, viruses, fungi, parasites. Our immune system protects us from them so that we don’t get sick.
But sometimes a germ (or pathogen) is able to get into our system – through a cut, from breathing in droplets from someone’s cough, or if our immune system has become weakened.
When this happens, our body launches an attack.
It starts with the white blood cells (or leukocytes). They’re our germ fighting cells. They patrol the body looking for foreign bodies like viruses. When they come across one, they immediately start to multiply. While they do this, they’re also sending signals to other immune cells to saddle up and get ready for battle.
There are two types of white blood cells: phagocytes and lymphocytes.
Phagocytes are hungry little buggers that eat pathogens for breakfast. They do this by surrounding the cell and absorbing it. When they do this they receive information from the proteins on the surface of the pathogen. These proteins are called antigens (or antibody generators). Phagocytes then send this info to the lymphocytes.
There are several types of phagocytes including neutrophils, monocytes, macrophages and mast cells. They all play important roles in the immune system.
Lymphocytes can be divided into B cells (they’re created in Bone marrow) and T cells (they’re created when they travel from the bone marrow to the Thymus).
B cells create antibodies. Antibodies neutralise the antigen by binding to it and disabling it. The antigen and antibody fit together like a key in a lock. As with a specific key working for a specific lock, there’s only one antibody that can fit each type of antigen.
T cells kill any of your infected cells. There are different types of T cells who have specific jobs in the immune response: Helper T cells and Killer T cells.
Helper T cells help…they send instructions to the other immune cells to help them get coordinated. They tell the B cells to create antibodies. They tell the Killer T cells to do what they do best – kill or destroy the cells infected by the pathogen. And they tell the phagocytes (specifically the macrophages) to join the party for a tasty pathogen feast.
When the battle is done and dusted, your body will keep copies of the antibody it created against this pathogen. That way if you encounter it again, you have a defence against it.
That’s your immune system in the very briefest of nutshells. It’s a highly complex, involved system that includes a lot of other cells, organs and body parts. Check out the More to Explore section for more info about the immune system.
Giving the immune system a head start – vaccines
Vaccines work by introducing your immune system to a virus or bacteria. This allows it to learn how to protect you from the pathogen before you meet it out in the world. A vaccine is a weakened or inactivated version of the pathogen. It causes your body to create antibodies. We have many vaccines at our disposal for diseases that cause people to get seriously ill – including measles, flu, tetanus, typhoid and polio.
There are currently more than 100 labs around the world researching and developing a vaccine for COVID-19. Read our blog to find out more.
When things go wrong – autoimmunity
Sometimes the immune system gets it wrong. Instead of attacking something foreign, like a virus or bacteria, it attacks healthy cells and tissues in the body. This is called autoimmunity. The attack causes inflammation and damage to the cells.
We don’t know why the immune system attacks its own body, but it’s thought that it may be the result of genetic factors (or things you’ve inherited) and something from the environment (e.g. a bacteria, virus or some medications).
There are many autoimmune conditions that are the result of a malfunctioning immune system. They include rheumatoid arthritis, lupus, ankylosing spondylitis, juvenile arthritis, Sjögren’s syndrome, coeliac disease and type 1 diabetes.
Stopping the spread of disease – herd immunity
There’s been a lot of talk recently about herd immunity – especially around COVID-19. But what does it mean?
Simply put herd immunity means that a large proportion of the population (or the herd) is immune to the disease. This can happen if they’ve been vaccinated or they’ve had the disease and are now immune to it. When most of us are immune to a disease, the disease isn’t able to spread as easily from person to person. The people who are immune create a buffer between the disease and those who can’t be vaccinated.
By building up this herd immunity, we not only look after ourselves (if we’re able to be vaccinated) but we help protect those who are vulnerable to infectious diseases – including babies, people with compromised or suppressed immune systems and older people.
The number of people we need to be immune to a disease to achieve herd immunity – the herd immunity threshold – varies from disease to disease. It depends on how easily transmissible and how infectious a pathogen is. For example, in the case of measles we need 92-95% of the population to be vaccinated because it’s incredibly infectious and the virus can survive outside the body for up to two hours. So even if you’re not in the room with an infected person, if you touch a surface that they’ve coughed or sneezed on, you can become infected if you’re not immune to the measles virus.
We don’t at this stage know what the herd immunity threshold will be for COVID-19. Estimates currently suggest around 60%. However we also don’t know if people remain immune to COVID-19 after they’ve recovered from an infection. So it may be that we only truly reach herd immunity if/when a vaccine is created and administered to the majority of us.
As with so much to do with this virus, we’re still learning and gathering data.
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More to explore
- Immune system explained
Better Health Channel
- How the immune system works
Medical News Today
- How does your immune system work?
- What is herd immunity and how many people need to be vaccinated to protect a community?
The Conversation, 1 August 2019
- What is herd immunity and could it work with COVID-19?
Snopes, 9 June 2020