At What Age Does the Immune System Weaken?
The immune system starts to become weak around the age of 60 years through a process known as immunosenescence. It is estimated that 2 billion people will have an age of over 60 by 2050 [1], and therefore, would be affected by immunosenescence.
What Is Immunosenescence?
Immunosenescence is the process of aging of our immune system which starts to perform less compared to that of a young and healthy individual. Our immune system is divided into two types: innate immunity and acquired immunity also known as adaptive immunity.
1- Immunosenescence of the Innate Immunity
Innate immunity is the first line of defense against bacteria, viruses, fungi, and toxins. This immunity is not specific to the invading pathogen but is rather based on the recognition of conserved features of pathogens, which make it react faster to help destroy invaders [2].
Innate immunity is carried out by natural killer (NK) cells, neutrophils, macrophages, and dendritic cells that are produced in the bone marrow by the hematopoietic stem cells.
While neutrophils, macrophages, and dendritic cells perform their activities through phagocytosis (internalization and destruction of pathogens), Natural killer (NK) cells have a cytotoxic activity through the recognition and release of substances that cause the cell death of the pathogen.
Although the activity of natural killer (NK) cells remains preserved, the phagocytic activities against pathogens of neutrophils, macrophages, and dendritic cells are reduced. However, the number of these cells does not appear to be affected.
2- Immunosenescence of the Adaptive Immunity
Unlike innate immunity, adaptive immunity is a more specialized type of immunity that involves the white blood cells, lymphocytes B, and lymphocytes T [3].
Lymphocytes B are the cells that produce antibodies against pathogens and cancerous cells, while lymphocytes T recognize and destroy pathogens and cancer cells through their cytotoxic activity by inducing cell death.
Lymphocytes B and lymphocytes T are also produced in the bone marrow by the hematopoietic stem cells and become mature in the thymus and spleen and after their activation. With the increase in age, the quantity and quality of lymphocytes B and T immune responses are significantly changed resulting in an impaired immune response.
Older individuals have a diminished capacity to respond to novel antigens (molecules on the outside of pathogens or cancer cells) and vaccines which results in increased susceptibility to infection and the development of age-related diseases such as cancer.
3- Immunosenescence and Inflammation
The function of immune cells is regulated by intercellular (between cells) communications that are mediated by cytokines, a small group of proteins that regulate inflammation. Cytokines are released by different cells in the body, including cells of innate and adaptive immunity.
Some of the cytokines promote inflammation and are known as proinflammatory cytokines, while others have anti-inflammatory activity. During immunosenescence, there is an increase in proinflammatory cytokines due to alterations in the function of immune cells [4][5].
Can We Slowdown Immunosenescence?
Immunosenescence can be slowed down through diet and therapeutic drugs that reduce inflammation.
1- Diet
A diet that is rich in fruits, vegetables, whole grains, legumes, and olive oil (e.g., Mediterranean diet) and that contains fewer sugars and red meat (e.g., cured meat) has been shown to reduce inflammation [6].
Probiotics and prebiotics that have been shown to reduce inflammation can also be provided through diet. For instance, probiotics are found in yogurt, lactobacillus milk, some cheeses such as Gouda, cheddar, cottage cheese, mozzarella, pickles, sauerkraut, kefir, kimchi, tempeh, kombucha, and miso.
Prebiotics are found in carrots, quinoa, radishes, onions, chicory roots, konjac roots, oats, yams, garlic, barley, wheat bran, berries, apples, asparagus, bananas, leeks, chia seeds, flax seeds, cocoa, coconut, jicama root, and dandelion greens.
2- Micronutrients
Micronutrients, such as vitamins and minerals, are critical for the good performance of the immune system. For instance, people with zinc deficiency (e.g., in older individuals) experience increased susceptibility to a variety of pathogens.
Zinc has been shown to have to be crucial for the function of immune cells such as neutrophils, natural killer cells, T lymphocytes, and B lymphocytes [7].
Other micronutrients such as vitamin C also reduce inflammation through its anti-oxidative stress activity.
3- Probiotics and Prebiotics
Probiotics have been shown to prevent inflammation associated with allergies, diabetes type 2 (Diabetes Miletus), autoimmune diseases, rheumatoid arthritis, cancer.
Because they produce lactic acid, the probiotics, Lactobacillus and Bifidobacterium, suppress pathogens’ induction of immunomodulatory molecules that can induce inflammation.
Prebiotics induce the expression of cytokines that promote communication between immune cells leading to improved immune response and protection against infections and other diseases such as cancer and neurodegenerative diseases.
The administration of the prebiotic fructo-oligosaccharides improves antibody response to viral vaccines, upregulates toll-like receptor 2-mediated immune response, and increased phagocytosis, and the levels of NK cells and the anti-inflammatory IL-10.
4- Bioactive Compounds
Resveratrol is a polyphenol found in red wine that has antiaging and anti-diabetic properties and is used as a nutritional supplement. Resveratrol has been shown to increase the levels of the NAD-dependent deacetylase sirtuin-1 (SIRT-1), a protein that is involved in the cellular response to inflammatory, metabolic, and oxidative stressors.
Sulforaphane (SFN) is an isothiocyanate that is present in cruciferous vegetables such as cauliflower, cabbage, kale, garden cress, bok choy, broccoli, and Brussels sprouts. Sulforaphane has been shown to inhibit inflammation by inhibiting the pro-inflammatory factor NFkB and by promoting antioxidation via the induction of NrF2, a master regulator of detoxification, anti-inflammation, and antioxidation processes within the cells.
Conclusion
Immunosenescence is a natural process of aging that results in alterations in the immune system leading to increased susceptibility to infections, reduced response to vaccines, and increased inflammation. However, immunosenescence can be slowed down through appropriate and healthy diets and food supplements that help the function of the immune system.
References
[1] https://www.who.int/news-room/fact-sheets/detail/ageing-and-health
