I have come to believe and often share with patients that the foundation of a baby’s overall health is their gut! If I could record myself saying that ‘the majority of their immune system lives in their gut’ and replay it to every patient, I think the tape would wear out!
Have you ever wondered actually what that means? Today, I will walk through the very basis, at a high level, of how our immune system works! This blog post is for the nerds (like myself) who like to know the ins and outs.
The Immune System
The immune system comprises all the organs that work in their little bodies to fight against infection and regulate the body’s inflammatory response. This is to fight off allergens, bacteria and viruses. The infant’s immune system, often mischaracterized as “immature,” is naïve to its new extra-uterine environment. There are two systems within the immune system. Innate and adaptive. Here is a high-level summary so we can simplify it. A pathogen enters the body, and the innate immune system is its first line of defence. Amongst other roles, this system is the one that tells the body to mount an inflammatory response; it’s like calling in the troops to start to say to the body, ‘A pathogen is here, and although we don’t know its name, we know it’s not self and we want to get rid of it.’
Innate Immunity
The innate immune system alerts the adaptive immune system via cytokine production and t cell activation to say, ‘HEY, take a look at this bad guy; I’ve brought him in, alerted a bunch of inflammation to surround him, yet now you, (the adaptive immune system) need to identify who this bad guy is and start to produce the actual t cells that will A) kill him off and B) that will tell the body to remember the face of this bad guy so we don’t let him into our body again.’ (I’m remarkably good at run-on sentences, don’t you think?!).
The innate immune system is the first line of defence in our body. This includes the following:
- The growth of the microbiome on the skin is the origin of the innate immune response in that the first line of defence is our skin! Our skin has a pH of 3 – 4, which stops the growth of micro-organisms. This is quickly developed at the very beginning of life.
- Their mucous membranes, for example have cilia and can trap microorganisms and expel them from the body
- Fevers are mounted and heat out the bacteria/virus/other pathogens
- Gastric acidity – is another portion of the innate and can break down viruses and bacteria. Acid pH in the first days of life settles into 3 – 4, which is that of an adult
- Complement pathways include adding proteins on microorganisms that then form pores in the membrane of the target cell, which triggers opsonization (exploding the microorganism) and triggers a local inflammatory response
- The inflammatory response is produced in the area of infection and promotes immune cells to come in and help fight the infection. This is when you see redness, heat, pain, swelling etc.
- Lastly, how the innate immune system then connects with the adaptive system via monocytes circulating in the blood, which turn into macrophages or dendritic cells in the tissues. They stimulate the adaptive immune system as mentioned above.
Adaptive Immunity
The adaptive immune response is what creates the memory of the antigens (part of the pathogen, i.e. bacteria, virus, etc.) that are presented.
Here are the various parts
- CD8 t cells are killer cells; they’ll do the dirty work – they’re like the ‘bang, you’re dead- type of assassin.
- CD4 differentiate further into T helper cells 1, 2, 3, 9 17 (plus many more) and each of these play a role. For example, Th1 tells other cells to come in and kill and make antibodies for bacteria and viruses, Th2 stimulates cells for an allergen reaction and builds antibodies for allergies.
- B cells, which are the antibodies that are produced that ‘hold’ the memory of the antigen, can be activated independently of t cells; however, they produce a weaker memory.
- B cells can also get activated by t helper cells – this is the basis of immunization. This has longer term more effective memory. The stimulated b cells then become plasma cells forming IgM and IgG antibodies. IgG is what we deal with in vaccines.
Interesting fact: There is a lot of research around the topic of whether babies at birth and within their first year of life can mount a Th1 immune response. Remember, the Th1 immune response will then tell others to kill off that virus or bacteria AND tell the antibodies to be produced against viruses and bacteria. This is the process in the body that the effectiveness of vaccines depends on. This is possibly why our scheduled routine vaccinations are multiple at two, four, and six months.
Digestion and the Immune System
As I mentioned (play the tape, please), ‘the majority of babies’ immune systems live in their gut’!
Part of our innate immune system (first line of defence) sits in the mucosal lining – gut, lungs, etc. It sees any foreign body (virus, bacteria etc) and calls all its buddies to action. Examples of these are antigen-presenting cells (APCs), neutrophils, natural killer (NK) cells, and mast cells.
In the gut,
- NK cells sit in the lining
- Mast cells are regulated by the microbiome
- APCs are interesting in the gut as they can differentiate between the microbiome bacteria and the bacteria from outside the body – allowing them to then present that cell (the bad guy) to the adaptive immune system.
Immunoglobulin G (IgG) are the guys that grasp onto foreign substances (viruses, bacteria, mould, etc.) and wave their hands at the T cells to come and walk them away from the bar and out the digestive lining or down the street and out of town, lol! This is the basis of food sensitivities in babies.
Immunoglobulin A (IgA) lives in the digestive lining. It identifies foreign pathogens and blocks them from entering the bloodstream and making babies ‘sick’!
As you can see, the more we take care of babies’ guts, the less inflammation is produced and the less prone they are to infections, inflammation, or autoimmunity down the road!
How do we take care?
- Breastmilk if possible
- A whole foods approach to solid food introduction
- Use antibiotics with caution and alternatives if possible
- Reduce ‘stress’ in these little cute thangs!
