The Wonders of Our Immune System
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What the immune system does for us everyday is simply amazing. It protects us against an onslaught of microorganisms that could infect and kill us. A basic understanding of the immune system allows us to see how important it is for our overall health and wellbeing.
It also allows us to see how nutrition and our lifestyle can have a major impact on immune function. Interestingly, the story begins in an organ you do not typically associate with the immune system: your bones.
Within our bones lie 2 types of bone marrow: yellow and red. Yellow marrow is mostly fat and relatively inert from an immune perspective. Red marrow contains a special form of stem cells which give birth to red blood cells as well as every type of immune cell coming from two lineages: myeloid and lymphoid.
Myeloid Cells: First Responders Of the Immune System
The myeloid lineage becomes your first responders. These are the cells that hang out in your tissues to help protect against infection. They include various immune cells called macrophages, neutrophils, and dendritic cells (more on these below). These cells fight anything they recognize as invaders.
When a bacteria or virus infects our tissues, macrophages are the first on site, recognizing invaders and gobbling them up. When cells sense infection, they send out signalling molecules called cytokines that attract more macrophages to the scene. Though quick on the scene, they fatigue quickly. When they do, they release cytokines to attract neutrophils and increase tissue fluid you recognize as inflammation. Neutrophils are great, but reckless. They kill invaders, but also damage tissues.
Next in battle are dendritic cells. These cells are a bridge between the generalists working right now, and the specialists you hope to recruit. Dendritic cells not only kill invaders, they chop them up into pieces called antigens (think of this like a piece of code the immune system can recognise) and express them on their cell surface. This helps our immune system target this specific antigen.
Lymphoid Cells: Specialists Providing Long Term Immunity
Dendritic cells leave the scene of the crime and encounter the first cells of the lymphoid lineage: T helper (TH) cells. TH cells are kind of amazing. They have a catalogue of every single antigen you may encounter. This is akin to a library with billions and billions of books.
Dendritic cells are bumping into each TH cell to find the one that reacts to one of the antigens. When they do, that TH cell begins cloning itself, sending half of the new recruits to the site of battle. They battle the specific microorganism they target and revive fatigued macrophages.
The other half of the cloned TH cells travel to lymph nodes to activate the other type of lymphoid cell: B cells. This causes B cells to clone themselves and create antibodies that help identify invaders for the rest of the immune system and incapacitate them.
When TH cells and B cells do long term battle, they create memory T and B cells that keep a record of the infectious agent. This allows you to maintain immunity against this invader for a period of time. Otherwise, you could immediately be reinfected.
The Lymphatic System: Superhighway Of the Immune System
While immune cells travel to tissues via the blood, all the magic happens in the lymphatic system. The lymphatic system contains lymphatic vessels that carry fluids away from organs and tissues. Though it eventually dumps into the bloodstream, there are hundreds of little organs known as lymph nodes that act as filters. The spleen is essentially a giant lymph node.
T and B cells hang out in lymph nodes where they get activated and cloned. This is why your lymph nodes get swollen when you get sick. Pumping action from your muscles help move lymph through the vessels and nodes, helping to filter infectious agents.
One final important organ within this system is the thymus gland. The thymus functions as a training ground for your T cells. It helps them mature and eliminates T cells that react with your own tissues. When the thymus functions poorly, you are less capable of forming long term immunity. You also become more prone to autoimmune disease.
Interestingly, the thymus begins to shrink in size early in life as healthy tissue is replaced with fat. It shrinks in size by 50% from birth to age 161, but immune function does not decline until middle age. Though there isn’t a great way to test immune function, most healthy adults experience approximately 4 infections per year. Those who experience more, or who have autoimmune disease, likely have lower immune function.
Improve Immune Function With a Healthy Lifestyle
With a basic understanding of immune function, you can see why lifestyle is so important. During ageing and obesity, a chronic state of inflammation causes your bone marrow to produce more myeloid and fewer lymphoid cells.2 This can lead to a chronic state of inflammation. It also converts red bone marrow, which produces important red blood cells (for energy and transport of nutrients), white blood cells and platelets (help with blood clotting and infection), into the more inert yellow bone marrow.3, 4
Poor sleep, night shift, and erratic schedules negatively impact nearly every aspect of immune function. Basically every cell of the immune system is under circadian control. This means they function best when you follow a regular schedule with the light, dark, feeding, fasting, moving and resting cycles of the day.5 So anything that disrupts circadian rhythms impairs immune function.
Gut health is also important. The gut is a source of sterile, chronic inflammation that may drive the increased inflammation in ageing and obesity. Furthermore, increased intestinal permeability creates a temporary state of thymic involution, meaning this important gland shrinks in size and the ability to produce important immune cells decrease.6
High levels of physical activity are also important to push lymph through lymphatic vessels and the lymph nodes that filter lymph. It also causes immune cells to traffic to tissues to prevent infection.7
Finally, nutrition is crucial to proper immune function. Nutrients shown to help support the immune system include zinc, vitamin C, vitamin E, omega-3 fatty acids, vitamin D.8 Probiotics may also be useful, with newer evidence indicating a reversal in age- and obesity-related thymic involution with a strain of Lactobacillus casei in mouse models.9
| If you want to learn more about the immune system and how you can improve the immune function with your lifestyle, come and join our free webinar on this topic on February 9th. The webinar is a collaboration with Food Pharmacy and we are privileged to have Lina Nertby Aurell hosting the webinar. To read more about the webinar and to sign up, click here (Note! The webinar is in Swedish). Welcome! |
This article was originally published as a guest editor post at foodpharmacy.se
By: Graeme Jones, clinical physiologist and CEO at Nordic Clinic Stockholm.
References
1. https://www.pnas.org/doi/10.1073/pnas.1714478115
2. https://www.frontiersin.org/articles/10.3389/fragi.2021.732414/full
3. https://onlinelibrary.wiley.com/doi/full/10.1111/acel.13671
4. https://pubmed.ncbi.nlm.nih.gov/19721009/
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4090048/
6. https://journals.sagepub.com/doi/10.1177/2058739218823466?icid=int.sj-abstract.similar-articles.1
7. https://pubmed.ncbi.nlm.nih.gov/18198659/
8. https://www.frontiersin.org/articles/10.3389/fimmu.2018.03160/full
