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Immunity is the ability of our body to resist harmful germs such as bacteria, viruses, fungi, and toxins.
The immune system is a complex network of different organs, cells, and proteins that together help keep us healthy.
This article is a summary of everything you need to know about immunity.
Types of immunity
The immune system is built of two components:
- the innate or nonspecific immunity
- the adaptive or specific immunity
We discuss them in turn.
The innate or nonspecific immunity
This is the defence system you were born with. The innate immunity is there to recognize and destroy microbes that enter our bodies from the outside environment. When encountering an outside invader, the innate immunity is extremely fast acting. A shortcoming of this type of immunity is that it has a single way of responding to all pathogens which does not factor in the differences between the invaders, which is why it is also called non-specific.
The innate immune system includes:
- Physical Barriers
Physical barriers are the first line of defence. They act as a barrier between the external and internal environment. These are:
- skin;
- the digestive and respiratory tracks;
- the nasopharynx;
- cilia and eyelashes;
- the mucous membranes located in our ears, nose, mouth, throat, lungs, and stomach.
- Chemical Barriers
These are the digestive enzymes that occur in the mouth, stomach acid, skin pH, saliva, and tears. These enzymes are powerful in fighting the bacteria: the acid on the surface of our skin prevents bacterial growth; the enzymes in saliva and the tears can break down bacterial cell walls; a highly acidic environment created in our stomach kills many pathogens entering the gastrointestinal tract.
- Internal defences
These are the proteins in the body. They react to bacteria cells and viruses and provide what is known as a complement system or a complement cascade of inflammatory and killer responses from the white blood cells.
One such protein is Interferon. It interferes with viruses and warns the immune system of the presence of germs and cancer cells.
Immunoglobulins – proteins that are also known as antibodies – bind to bacteria and viruses and destroy them. They are found in the vast surfaces called mucosa surfaces located in mouth, nose, lungs, stomach, bladder, etc. The most abundant out of all types of immunoglobulins present on the mucosa surface is immunoglobulin A (IgA). It inhibits bacterial and viral adhesion to cells and stops the spread of germs.
- Cytokines
These are molecules that regulate immune response to infection or injury.
- The gut microbiome
Our digestive system is home to trillions of microorganisms – bacteria, viruses, fungi – known collectively as the microbiome.
The gut microbiome is crucial to our health because it helps to regulate the equilibrium in the gut, known as homeostasis. Homeostasis is achieved because of an incredible diversity of bacteria in the microbiome. Some of these bacteria are good whilst some are associated with diseases. Whenever inflammatory processes occur in the gut, friendly bacteria restore equilibrium by boosting our immune system.
These are some of the ways that friendly bacteria protect our health:
- They compete for food and tissue receptors with bad germs.
- They produce toxic substances which can destroy pathogens.
- They stimulate antibody production.
We can increase the diversity of friendly bacteria by making changes to our diet.
- The adaptive or specific immunity
The function of the specific or adaptive immunity is to recognize and selectively destroy pathogens (e.g. tumor antigens, transplanted antigens, etc.). Unlike the innate immune system, the adaptive immune system does not act fast as it takes time for it to recognize the pathogens. But once the adaptive immune system recognized the foreign microorganism, it will be effective in fighting it, and it will be able to quickly identify the same pathogen the future.
Adaptive immunity can be active or passive.
Active immunity develops through our daily exposure to bacteria and viruses. We develop immunity either when we recover from an infection or when we get vaccinated against it.
In some cases, this immunity stays for life. For example, measles and chickenpox immunity is predominantly for life. In other cases, immunity is shorter-lived. For example, gastrointestinal infections or viral respiratory infections circulate seasonally and, if infected, you are only immune for a season.
Passive immunity develops when someone receives antibodies to a disease from an external source. An excellent example of passive adaptive immunity is breast milk. A newborn baby is protected from various infections thanks to immunoglobulins in breast milk.
The adaptive and innate immune systems work together to eliminate pathogens and protect our bodies. For example, phagocytic cells – the primary weapon of non-specific immunity – play important role in the specific immune responses. Conversely, humoral factors produced by adaptive immunity (via the immunocompetent cells), regulate an innate immune response (by enhancing the activity of phagocytes).
The Genetics of Immunity
Our immune responses are controlled by our genes. And our genetic makeup is what we inherit from our parents. As such, we can have a genetic predisposition or genetic susceptibility to particular diseases.
In some instances, problems in the genetic code cause a group of disorders called primary immunodeficiency (PI). Some of the conditions associated with PI are
- Wiskott-Aldrich syndrome.
- Severe combined immunodeficiency disease (SCID).
- DiGeorge syndrome.
- Ataxia-telangectasia.
- Chronic granulomatous disease.
- Bare lymphocyte syndrome.
We also inherit the gut microbiome. In addition, our environment is also very important to the health of the microbiome. For example, the diversity of a baby’s gut microbiome depends on the way they were born. Babies delivered naturally receive their first dose of the microbiome by passing through the birth channel. Babies delivered by a caesarean do not receive this, and it is recommended to supplement the diet of the babies delivered by C-section with age-appropriate probiotics.
Immunity and Nutrition
It might not be obvious, but nutrition is extremely important in the formation of a healthy immune response. Here we will look at some vitamins that help to boost our immune system, and list foods rich in them.
Vitamin C
Vitamin C It is a powerful antioxidant and has an anti-inflammatory effect. It is amazingly fast acting and works wonders at the time when you are sick, including shortening duration of common colds.
A great way to boost your immune system is through eating foods rich in Vitamin C.
Vitamin C-rich products
- Citrus (oranges, kiwi, lemon, grapefruit).
- Spinach.
- Kale.
- Bell peppers.
- Brussel sprouts.
- Strawberries.
- Papaya.
- Tomatoes.
- Cruciferous vegetables (broccoli, Brussel sprouts, cabbage).
Vitamin E
Just like vitamin C, vitamin E is also a powerful antioxidant and helps the body fight infections.
A study of vitamin E supplementation in healthy elderly participants has shown an improved function of T-cells which play a critical part in our adaptive immune system.
Vitamin E-rich products:
- Pumpkin.
- Almonds.
- Sunflower, safflower, and soybean oil.
- Sunflower seeds.
- Peanuts, peanut butter.
- Beet greens, collard greens, spinach.
- Red bell pepper.
- Asparagus.
- Mango.
- Avocado.
Vitamin A
Vitamin A has anti-inflammatory properties and plays an important role in enhancing immune functions by regulating immune responses and the growth of T-cells.
Vitamin A deficiency can cause problems with the first line of defence: skin and the mucous membrane.
Vitamin A-rich products
- Kale.
- Spinach.
- Carrots.
- Sweet potatoes.
- Pumpkin.
- Tomatoes.
- Red bell pepper.
- Beef liver.
- Fish oils.
- Milk.
- Eggs.
Vitamin D
Vitamin D is an immune system booster. It can regulate both innate and adaptive immune responses.
A recent study shows that vitamin D has multiple positive effects on our immune system, including increased activity of phagocytosis and T-cell activation.
Vitamin D-rich products
- Salmon.
- Herring and sardines.
- Egg yolks.
- Mushrooms.
- Red meat.
- Liver.
Zinc
Zinc is essential for normal metabolic reactions.
Zinc deficiency negatively affects T-cells development.
A study showed that low zinc increases the risk of pneumonia in the elderly.
Zinc-rich products
- Rock oysters.
- Beef.
- Crab.
- Oats (rolled, uncooked).
- Chicken breast.
- Milk.
The role of exercise in healthy immunity
Regular physical activity helps to manage weight; reduces the risk of cardiovascular diseases and the chances of getting cold, flu, or other illness; and boosts the immune system.
The material is based on research:
- Vitamin C for preventing and treating the common cold
- Vitamin E supplementation and in vivo immune response in healthy elderly subjects. A randomized controlled trial
- Vitamin D and Immune Function
- Zinc and immune function: the biological basis of altered resistance to infection
