Alright, we have to start with the big questions. Like, for example, tea or coffee? And if you say tea, milk in first or second? (Answer: tea with milk in second, obviously. We're all civilised people here).
Seriously, though, whatever your choice of drink, you might want to make one and settle in. Because we're starting BIG.
How does the immune system work?
First up, the immune system is made up of two smaller systems. Yup. There's two. They work together and both are equally important for the protection of the host organism (which means you, me, or the dog currently eyeing up the biscuits waiting next to your tea). These two systems are divided on the approach they take to host defence and are referred to as innate or adaptive immunity. The key features are summarised in the image below.
Innate immunity is in many ways like your local police force. Always on patrol, it can respond quickly to any site of damage or infection and is often enough to contain or stop infection before you can get sick. Physical barriers include your skin, the mucus lining of your respiratory tract, the acid of the stomach, and even your tears and saliva. Even the beautiful bacteria that live on and in you (your microbiome) can be included, as many actively discourage the presence of new, potentially harmful bacteria. It also includes non-specialised cells like the phagocytes (macrophages and neutrophils). These will be discussed further in another post (click here). Unfortunately, many of the mechanisms by which the innate immune system works involves causing a lot of damage. Remember your last sore throat? Yeah, your local police cells apologise for that...
Between innate and adaptive immunity lie our lovely dendritic cells. They are the green arrow in the diagram above, as they link the two systems together. While not strictly part of adaptive immunity, they are essential for alerting the adaptive system to danger and provide the information needed for proper training and selection of the adaptive immune cells.
Adaptive immunity comes into play when innate immunity is not enough to cope with the infection. Much like the military, it is highly specialised and far more effective at removing invaders from the body. It is slower to act though, as it has to be 'trained' to fight every new infection. We will discuss this more later. But the amazing thing about it is it's ability to 'remember'. Every time you encounter the same pathogen (bacteria or virus, usually), it gets faster and better at responding. This is what immunisation aims to improve (again, see a future post for more). B cells, T cells and antibodies are the main players in this group.
Together, the innate and adaptive systems act to protect us from almost every pathogen we encounter. Of course, it's not always a successful battle - that's when it's time to pay a visit to the doctor and get your little white cells some help. But considering just how many bacteria, viruses and every other kind of microorganism we encounter on a daily basis, I'd say they're doing a pretty good job.
Now take a sip. You've earned it.
---------------------------------------------------------------------------------------------------------------------------
For (a lot) more info, check out:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6156898/
Note: I should point out now that one of my posts is a glossary page which includes explanations for any words that I think need them. If a word is missing that you think should be there, please let me know.