Since everyone is most likely at home, with a bit more time on their hands, I thought it only appropriate to delve into the topic of our immune system.
With the ongoing COVID-19 pandemic, now more than ever, it is essential to understand what your immune system is and how you can help to keep it functioning well (and what that means).
Over the coming weeks, we'll be talking about all things immune system, starting today, with a brief overview of what our immune system is, how it works and where it's located.
Fig 1: A cell preparing for battle with a virus
The Immune System
Simply put the immune system has the job of detecting foreign invaders of the body, such as toxins, viruses, bacteria, and any other compounds or organisms that don't belong to us, and might cause us harm.
The immune system can distinguish between healthy and unhealthy cells by identifying what is known as "danger-associated molecular patterns (DAMPs). Infectious microbes (such as the coronavirus) release a set of signals recognised by the immune system as pathogen-associated molecule patterns (PAMPs). 
Fig 2: Healthy vs Diseased lungs, alveoli & epithelium.
There are two main branches of our immune system known as our innate immune system and our adaptive immune system.
Innate Immune System
This is our bodies non-specific first line of defence for trying to keep nasty things out and includes:
Physical/ structural barriers (like mucous in the nasal passage)
Chemical barriers (like stomach acid)
Protective cells (like our natural killer (NK) cells, white blood cells that can destroy harmful invaders)
Adaptive Immune System
The is a more specialised branch of the immune system that kicks in when the innate immune system has prevented the infiltration of a pathogen.
It fights infections by preventing pathogens from colonising and destroys microorganisms like virus and bacteria with an army of T cells and B cells. These are specialised white blood cells that mature in the thymus and bone marrow, respectively.
Fig 3: Immune system cells (natural killer, t and b cells)
And what's amazing about our immune system is that they have a "memory" of sorts. Once they've recognised and identified a certain pathogen they adapt to fight it. This is where the phrase "building immunity" comes from - generally strengthening the adaptive immune systems ability to recognise and identify hostile invaders. This is the premise on which vaccinations work - exposing your body to a tiny dose of a pathogen, and it will know what to do when confronted with a bigger one.
Where Is The Immune System?
As previously mentioned a lot of the specialed immune system cells are produced in the bone marrow. But they lie dormant in what's known as the lymphatic system.
The lymphatic system is a network of vessels and tissues that act as a highway for immune cells to be carried through. The immune cells converge at lymph nodes, which are found throughout the body.
The lymph nodes are little communication hubs where immune cells gather information bought in from the body. For example, if an adaptive immune cell in the lymph node recognises a virus brought in from a distant area, they will activate, replicate and leave to fight the pathogen. Thus if you are suffering from swollen lymph nodes you are having an active immune response to a foreign invader.
Fig 4: Lymphatic System and Lymph Nodes
Inflammation Is Good... In Moderation
Inflammation is what we call the response of our immune system to pathogens, damaged cells and toxic compounds. So inflammation is a defence mechanism that is vital to our health.
Usually, during acute inflammatory responses, cellular and molecular events and interactions efficiently minimise impending injury or infection . Essentially saying, when something is able to do small amounts of harm to our body - inflammation kicks in and repairs things. This restoration is known as homeostasis - a stable equilibrium.
There are numerous examples of an acute inflammation response including exercise. That's right, exercise triggers the body's defence mechanism. Which seems strange? Since exercise is meant to be good for us?
You see, moderate exercise causes trauma to the muscle fibres, basically injuring them by creating small tears. But, once the muscle is injured, its organelles respond with inflammation by activating special "satellite cells" which are located near the muscle . These satellite cells repair the muscle, create a larger cross-sectional area (hypertrophy) or even create new muscle fibres themselves!
(This is assuming you give yourself enough rest and recovery to stimulate the release of human growth hormone and insulin-like growth - both of which stimulate satellite cells to do their work.)
So inflammation can help fight off pathogens and help us get stronger! Great! But, chronic inflammation can also be a bad thing.
If we don't give the immune system enough time to heal between bouts of invaders it can't return the body to homeostasis and as such we end in a state of constant inflammation. For example, chronic alcohol consumption impairs liver function leading to persistent inflammation and ultimately, organ damage .
Our immune system is the body's defence mechanism against foreign invaders such as toxins, viruses and bacteria.
There are two main branches of the immune system, our innate and our adaptive systems. The innate system consists of physical structures and natural killer cells whereas, the adaptive is a host of t and b cells that are triggered once the physical immune system has failed. These specialised white blood cells attack pathogens to stop them from colonising.
The t and b cells of our adaptive immune system are produced in the thymus and bone marrow but are transported around the body via the lymphatic system. Various lymphatic nodes around the body store information bought in by immune cells so they are prepped and ready to fight future invaders.
Inflammation is the defence mechanism our body activates when pathogens, damaged cells or toxic compounds are detected. Inflammation is a sign the body is fighting infection and trying to restore the body to homeostasis. Inflammation can be caused by a host of factors such as exercise and alcohol consumption. With enough rest and recuperation, the body will restore balance, but without enough time to do so, chronic inflammation can occur.
So there we have it. A brief and concise overview of the immune system and its basic function. Now, more than ever, having a well functioning immune system is of paramount importance to people's health. Our next article will be aimed at providing you with scientifically proved ways you can boost your immune system - all done from home.
Stay safe everyone and we will beat this coronavirus together!
 - Precision Nutrition, Unit 2, The Science of Nutrition, Pages 232-240
 College of Veterinary Medicine, Sichuan Agricultural University, Wenjiang, Chengdu 611130, China
 Alcohol, inflammation, and gut-liver-brain interactions in tissue damage and disease development, World J Gastroenterol. 2010 Mar 21; 16(11): 1304–1313.
Published online 2010 Mar 21.
 BEYOND TRAINING, Ben Greenfield, pages 149-151
Figures 2-6: All figures produced on biorender.com