Days are getting shorter and we have all noticed the drop in temperature even on sunny days. Fall is here! Thanksgiving, pumpkins and beautiful foliage are all part and parcel of the coming season. Autumn is historically a time for harvest, taking stock and preparing for the coming hardships of winter. This principal can also be applied to your health. Now is an ideal time to take stock of your body and help set yourself up to fight off that winter virus or even avoid it completely. In order for you to help maintain and improve your body’s defence system it may be helpful for you to have a better understanding of how it works.
Your body is constantly bombarded by bacteria, fungi and viruses, amongst other things. They are in your home, on your skin and even in the air you breathe. While quite a number of these are harmless, many of them are potentially dangerous to us. The name given to these infectious agents (including bacteria, virus, prion, fungus, or parasites) is pathogen. If you think about it, the human body is a perfect home for these pathogens. A warm moist environment such as that found in the human respiratory tract is exactly what they need to grow and multiply . Luckily for us, the human body has evolved a number of ways to protect us from an invasion. As with all parts of the human body and its inner workings, the immune system is incredibly complex. For the purposes of this article we will try to keep things as simple as possible.
The immune system is not a combination of organs such as the digestive system or the nervous system. Rather is it functional system that involves a number of organs, molecules and immune cells. Many of the organs involved in the immune system have other functions too. The immune cells (of which there are trillions) live in the lymphatic system and the blood and other body fluid.
Skin and Mucosa – Innate Physical Defence
The skin is the largest organ of the human body. It provides a physical barrier between the outside world and your body. The epidermis or outermost layer of the skin is made up of highly keratinized cells. This layer is resistant to most bacteria enzymes and toxins. Mucous membranes line all body cavities that open to the exterior. Examples of these are the digestive system and the respiratory system, reproductive tracts and urinary tracts. The lining inside your mouth is an example of a mucous membrane. Apart from physical barriers these organs also produce secretions such as sebum on skin, hydrochloric acid in the stomach, saliva in the mouth and tears in the eyes, which contain enzymes and chemicals to inhibit or destroy bacteria. The skin and vaginal mucosa maintain their PH at a level that also makes it difficult for pathogens to survive. Sticky mucous at the body’s orifices traps pathogens and prevents them from entering the body. Along the upper respiratory tract you will find tiny hair like structures known as cilla which sweep dust and mucus towards the mouth thus preventing it from traveling further into the body.
These are a type of white blood cell that essentially guard and patrol every border of the body. If the skin and mucosa are breached these cells are usually the first to come upon the pathogen. They work by engulfing the pathogen and secreting enzymes, free radicals and even hydrogen peroxide (bleach) in some cases. Sometimes the chemicals secreted depend on the type of pathogen. If the pathogen is too big for the macrophage to engulf it will secrete it’s chemicals into the area surrounding the pathogen in order to kill it. Often macrophages can handle the pathogen on their own as they are capable of engulfing up to 100 pathogens each. Macrophages will also communicate to other immune cells to bring them to the area. They can also cause the cells of the surrounding blood vessels to flood the area with fluid making it easier for the immune cells to work in the area. This is part of what causes swelling and inflammation in an area where the immune system is at work.
Neutrophils are another type of white blood cell very similar to macrophages, these cells are found in the blood. Once alerted to the presence of an intruder (usually by a macrophage) neutrophils will travel to the area. They are very aggressive and will often kill healthy cells and themselves while in the process of removing a pathogen. They engulf and kill in a similar way to macrophages and they also create barriers around pathogens to prevent it spreading. They will also trigger the next line of defence. Neutrophils will commit suicide after 5 days to prevent them becoming too prolific and causing damage within the body.
Natural Killer Cells
Once the pathogen has managed to infect a healthy cell, the healthy cells send out a stress signal. The natural killer cells, found in the blood and lymph, recognize that this cell is infected and kill it. Unlike the previous cells they do not engulf the cell but attach to it to induce apoptosis (cell suicide). The infected cell dies and takes the pathogen along with it. Natural killer cells also act to enhance the inflammatory response first triggered by the macrophage.
This response is activated when any trauma occurs to the body e.g. a blow, a burn, a cut or an infection. The signs of inflammation are redness, heat, swelling and pain. This is a normal part of the healing process and not always indicative of an infection. Heat and redness are caused by increase blood flow to the area which brings more immune cells to fight any potential infection. There is also an increase in fluid surrounding the cells in this area, leading to swelling. This fluid contains chemicals to promote inflammation and draw more immune cells to the area. It also contains interferon and complement which kill virus infected cells, and helps the healthy cells resist infection and intensifies the body’s response. The build up of fluid causes swelling which presses on nerve endings in the area and can cause pain. Pain may also be caused by the pathogen itself releasing toxins. The increase in fluid in the area helps to dilute any harmful chemicals a potential pathogen may produce and the fluid also contains important chemicals such as clotting factors which help to form a protective barrier and contain the area. The pain and swelling also restrict movement in the area forcing us to rest it and allow for healing to occur.
All these factors can occur before the body has even worked out what it is defending itself against. These responses happen regardless of the pathogen and are known as the nonspecific immune response.
B-Cells, T- Cells and Dendritic Cells- Adaptive immunity
Antibodies found on B-cells (another white blood cell) activate the complement that in turn interferes with the pathogens ability to function. The antibodies are made by the B-cell from pieces of the pathogen. The dendritic cell, sometimes known as the brain of the immune system, eats part of the pathogen and decides what kind of cells are needed to fight the infection. It then calls on the appropriate cells to the area.
Helper T cells release chemicals which aid antibodies and call more macrophages and neutrophils to the scene.
Cytotoxic T cells also receive the signal and secrete chemicals to get the infected cell to die and take the pathogen with it.
Regulatory T Cells are the cells which slow the immune response by releasing chemicals. These are the cells responsible for calming down the immune response once a threat has been overcome. These cells also play an important role in preventing autoimmune reactions.
Memory Cells (which can be made from B-cells or T-cells) are produced by the body during the course of an attack on the immune system. They can remain in the body for years after the infection and enable our bodies to mount an even faster response in the event of another attack by the same pathogen. Often they will enable the body to react so quickly that you will never even know your body is under attack.
Other areas of the body involved in our immunity include the bone marrow where blood cells including those discussed are made, the thymus gland which produces hormones involved in the immune response, and the lymphatic system which is closely related to the circulatory systems and drains into it. Many white blood cells are found in the lymphatic system and during an immune response they travel from here to the site of infection. This is why during an infection you may notice swelling in the areas where lymph nodes are present such as neck and underarms.
Part of the body’s immune response may include a fever. It was previously thought that a rise in temperature simply aided the body to defend itself by making it difficult for bacteria to replicate and grow. However, new research is now showing that an increase in body temperature may actually help the cytotoxic T-cells (which kill infected and cancerous cells) to carry out their work more effectively. Some experts now believe that allowing the body to go through a mild fever may actually enhance the immune systems response and we should reevaluate how we treat mild fevers in the future. It is important to note that while a mild fever may be helpful, a very high body temperature can be dangerous. The normal range for your body temperature should be between 97.8 and 99.0F (36.5-37.2 C).
Your immune system can be a good indictor of your overall health. Contrary to popular belief, getting cold when wet will not make you more likely to catch a cold or flu this winter. However, things like stress, lack of sleep, poor diet and generally being run down could contribute to a less effective immune system. As such, maintaining a healthy happy lifestyle can help you to avoid becoming unwell this winter. Talk to your Naturopathic Doctor at Yaletown Naturopathic Clinic for advice on optimizing and boosting your health and immunity.
Human anatomy and physiology 7th ed. 2007. E. N. Marieb and K. Hoehn.
Fever Plays Vital Role in Immune Response. Infection Control Today. Nov 2nd 2011. Accessed on September 7th 2015. http://www.infectioncontroltoday.com/news/2011/11/fever-plays-vital-role-in-immune-response.aspx