The Immune System
The immune system is a complex and dynamic network of cells, membranes and organs. These entities all work together to protect us from infection and potential pathogens which include the opportunistic microbes, bacteria, viruses, fungi and parasites that are all around us – in the air that we breathe, the food we eat, the surfaces we touch. When potential pathogens enter the body, the immune system springs to work, neutralising them and eliminating them.
Innate & Adaptive Immunity
There are two major divisions in the immune system that are interlocking and complementary, the innate and adaptive immune systems.
The innate immune system is our body’s first line of defense against pathogens. It consists of our skin, our body enzymes such as saliva and stomach acid, and our protective epithelial cells, which line our body’s mucosal surfaces (such as the gastrointestinal tract). These physical factors along with specialised white blood cells can facilitate the destruction of pathogens. Elements of this system are essential to the initiation of the response of the adaptive immune system.
Our body’s adaptive immune system is far more sophisticated than the innate system and deals with specific fragments of any potentially harmful or foreign material. These fragments are called antigens and they are dealt with in the immune system by antigen receptors. Once an antigen receptor adapts to one of these invading fragments, it retains antigenic memory so that it may quickly neutralise that antigen if it invades the body again.
The inflammatory response
This is an essential tool by means of which the body identifies, isolates and mounts a concerted response to attack or damage. It is a vital part of the immune response but is tightly controlled. The inflammatory process is initiated by certain triggers (damage or infection, for example) and then halted when the stimulus is dealt with. It is when the immune system fails to switch off the inflammatory response that we can experience symptoms such as those associated with arthritis or hayfever.
A brief overview of the main active components of the immune system
This is a protein found in the blood. It is important for the recruitment of inflammatory cells and the killing of pathogens.
These are the major proteins that are produced by virally-infected cells. They can produce a state of viral resistance in adjacent cells.
Red blood cells
These are produced in the bone marrow and are mainly used to carry oxygen and nutrients around the body whilst also removing metabolic waste. They are concave in shape enabling them to transport compounds through the blood. However, some are misshapen so are less efficient and lack the ability to carry nutrients. These misfit cells are increased through over-exercise as well as poor nutrition.
These are the first cells to reach sites of inflammation and are involved in defending against fungal and bacterial infections. They destroy microorganisms by phagocytosis (a process which allows cells to engulf matter that needs to be destroyed) as well as the release of hydrolytic enzymes (those that can split bonds). Neutrophils are fast-acting, short-lived and their end product is pus.
Monocytes tend to be the largest circulating blood cell. They are the key cells for initiation of both innate and adaptive immune response and are also phagocytic. They act as carriers by taking particles of pathogens to T cells (see below) to trigger a reaction. Monocytes travel from the blood into tissue, and are then known as macrophages.
These cells release histamine, which is involved in the inflammatory response.
Their primary function is to combat parasitic infection, mostly in the gastrointestinal tract. They are also involved in allergic reaction, such as hayfever or hives.
Lymphocytes (B, T and NK cells)
Lymphocytes are produced in the lymphatic system, which takes fluids from the blood stream to the tissues. There are three main types: B cells, which make the antibodies that will cling to pathogens; T cells, which detect and act against mutant cells or cells that have become cancerous or infected by a pathogen and, lastly, Natural Killer (NK) cells, which destroy other infected or cancerous cells.
Issues that adversely affect the immune system
- Being run down, sleep-deprived or stressed.
- Diets of less than 1,200 calories per day.
- High intake of saturated fat and refined carbohydrates and sugars.
- Excessive exercise.
- Low intake of protein.
The food we eat is intricately involved in the working of specific immune cells due to the various nutrients it provides. Although all nutrients are involved in the immune system, some have a more direct role than others. As such, consuming foods high in these nutrients is an effective way to boost immunity.
- Vitamin A is involved with antibody production and cell replication. It also supports the thymus gland. Eggs, liver, cheese, apricots, sweet potato, butternut
- Vitamin C increases antibody production and is a component of both interferon and complement. Limes, lemons, berries, peppers, kale, kiwi fruit
- Vitamin E works as an antioxidant and can increase the concentration of T cells. Avocadoes, almonds, sunflower seeds, olive oil
- Vitamin B6 works to support by B and T cells. Chicken, lamb, eggs, legumes, brown rice
- Zinc is required by the thymus gland and essential for the manufacture of T cells. Seafood, chicken, oats, brown rice, pumpkin seeds
- Selenium is involved in the action of both NK and T cells. It is essential for antibody production. Seafood, brazil nuts, sesame seeds, kidney beans.
- Iodine stimulates NK cells. Seaweed, kelp, seafood, garlic
- Bioflavonoids trigger a response that works against carcinogens. They therefore have a potential role in warding off some cancers. Citrus fruits, green and white tea, red wine, dark chocolate.
- Organosulphides stimulate macrophage and lymphocyte action. Garlic, onions, shallots, leeks.
- Probiotics stimulate the immune response in the gastrointestinal tract. They can also crowd out bad bacteria and yeasts. Kefir, sauerkraut, yoghurt and miso.
The success of our immune system relies on an incredibly elaborate and dynamic regulatory/communications network composed of millions of cells and is a sensitive system of checks and balances. Biological errors and environmental invasions can result in the immune process going terribly wrong. Boosting the power of the immune system through clever food choices should be a top priority.
Marber I. Super Eating. 2008. Quadrille Publishing Limited.
Novak R, Griffin J. Immunology – Crash Course. 2006. Mosby.
Peakman M, Vergani, D. Basic and Clinical Immunology, 2nd Ed. 2009. Churchill Livingstone.