Skeletal Muscle: The Forgotten Part of the Immune System, By Mukaila Kareem
Frankly, “boosting” the immune system requires non-strenuous muscle contractions in form of regular exercise and thus promotes an anti-inflammatory environment. This sharpens the attack of immune cells and maintains the thymic production of battle-ready naïve T cell fighters against new invaders, with overall ability of older adults to withstand new infections and decrease vaccination failure.
The failure of modern medicine in preventing and curing modern chronic diseases partly rests on the inability to connect the dots between health, overconsumption, physical inactivity, and the immune system. Everyone knows that exercise is good, but few could explain how good and one bestselling author, a kidney specialist and proponent of fasting in diabetic reversal, stated that exercise is so good that it’s a waste of time talking about it. Permit me to digress here: Years ago, my son had an ear infection and insisted that his pediatrician prescribed amoxicillin tablets, instead of the liquid form to him because he thought that he was no longer a little kid. Besides, he loved and still loves West African pounded yam, which involves swallowing the good stuff in small balls after dipping it in soup.
However, he initially refused to take the tablets because he thought they were too big for him to swallow. I took advantage of his knowledge of animal cell biology, including the aggressive streak in boys, and informed him that the medicine worked to kill the bacteria that was causing him pain by piercing its “skin” and then releasing its contents to neutralise the bacteria. In addition, I informed him that the pain would come back or not go away if he missed the dosages because the bacteria would die only if he took them as prescribed. The point was he knew the medicine was good but understanding how it worked made the difference in swallowing the “big” pills.
Exercise sometimes means different things, based on circumstance, and with the ongoing coronavirus pandemic, exercise, to many, is a “booster” of the immune system. As I noted in my previous article, human beings are both instinctively and deliberately endowed with “disease avoidant” behaviours to prevent us from getting sick. For example, and this is in no way meant to gross you out, but be ready to have your own treat if you invite friends over and prepare the most delicious chocolate brownies and shape it like coiled faeces, with the placement of a few synthetic flies perched on the “pile”! The full awareness that it is chocolate brownies probably may not be enough for many to overcome the disgusting sight wired to avoid infection, despite the familiar smell of chocolate.
The question is: Beside inherent behaviours to avoid sickness, what are the roles of skeletal muscle as an important part of immune system in overall health, and given the present attention to COVID-19 and social distancing, why must we remain physically active during and after the ongoing lockdown? A short context applies here: Man is not the strongest being on the planet, but he is the smartest and the most intelligent. In addition, his bipedal locomotion is highly efficient and costs far less energy than the locomotion of four-legged animals. As the Holy Scripture says to man: “…be fruitful and multiply; populate the earth abundantly and multiply in it.” Therefore with the superb combination of unsurpassed the locomotion apparatus (legs/feet) and smartness (big brain), man has therefore been curiously nosey, not just exploring new environments but has thrived everywhere, even with the ability to reproduce, in the face of starvation, dehydration, accidents, violence and infections.
…the immune system is broadly divided into innate and adaptive categories. The innate immune system is the first line of attack once bacteria, virus, or fungus successfully gains entrance into the body. Primarily, the goal of the innate cells is to ingest these foreign bodies before they enter the body cells and this assignment is performed by innate cells called neutrophils and monocytes/macrophages.
Therefore, man’s constant migration, despite environmental challenges, requires an effective immune system in an anti-inflammatory mode as a preventive measure to stave off infections. However, in rest periods, such as overnight sleep, occasional accidents and infections, the immune system switches to a pro-inflammatory mode. To give a clearer picture, the immune system acts as a “watchman” for cell repair and cell production during overnight sleep, promotes wound healing following occasional accidents, and mounts an overwhelming response to severe infections causing sickness behaviour with little or no priority for physical activity, in line with an Italian saying: “prima vivi e poi filosofi” (First live and then philosophise).
Multiple studies have described the decline in immune function with age, which includes increased risk for new infections, recurrent infection from old antigens and decreased vaccine efficacy. In fact, it has been reported that the yearly influenza vaccine is only 40–60 per cent effective in people aged 65 and above. However, these studies, as always, did not reflect the roles of regular physical activity in immune competence.
Briefly, the immune system is broadly divided into innate and adaptive categories. The innate immune system is the first line of attack once bacteria, virus, or fungus successfully gains entrance into the body. Primarily, the goal of the innate cells is to ingest these foreign bodies before they enter the body cells and this assignment is performed by innate cells called neutrophils and monocytes/macrophages. However, if the invaders succeeded in entering and infecting the body cells, the infected cells are promptly recognised and dissolved by the innate cells called Natural Killers with their potent toxins. Natural Killers are so named because they do not require “training” and can attack all kind of invading antigens.
For an effective innate immune system, working muscles via regular exercise secretes anti-inflammatory proteins called myokines, which help to mobilise the increased circulation of immune cells. Even in the absence of infection, contracting muscles cause circulating neutrophils to release soluble anti-microbial and anti-cancer proteins called lactoferrin and lysozyme. These proteins are also found in saliva, nasal secretion, and tears. According to a study, a bout of 45 minutes of running significantly increases the production of lysozyme and lactoferrin in saliva. In addition, a 2004 paper also reported an increase of 15.5 per cent in circulating neutrophils following an hour of exercise, including a 33 per cent increase in serum lactoferrin concentration. In fact, the human’s first encounter with lactoferrin is in thier mother’s breast milk, and its protective antimicrobial properties, according to a review, allow newborns to allocate 74 per cent of their energy for brain growth, without wasting precious calories on fighting infections. Another study reported that regular exercise, despite aging, reduces the pro-inflammatory innate immune cells called non-classical monocytes, increases anti-inflammatory classical monocytes, acts to cause direct conversion of pro-inflammatory M1 macrophages to anti-inflammatory M2 macrophages and improves Natural killers’ toxicity to infected cells.
The production of naïve T cells by the thymus is highest at birth and during infancy, and accelerated reduction in thymic size and function is said to begin in the early 20s causing a high pool of old and exhausted memory T cells and low naïve cell census, thus leaving older people susceptible to infections and vaccination failure.
Furthermore, the age associated decline in immune function has been fully demonstrated in the adaptive immune system but again the protective effects of contracting muscles in immune competence has not generally been considered. Adaptive cells are specialist infection- and cancer-fighting T cells that derived their “T name” from and an organ called thymus, where they are trained to recognise and attack new antigens. Following “thymic education”, they emigrate to the blood circulation as naïve T cells to surveil the body for new infections. The high population of naïve T cells is necessary throughout life to prepare the body to respond to new infections that have not been previously encountered. However, once they have been presented with a new antigen, naïve T cells get activated and become specialist fighters only for that specific antigen and thus transform to a small pool of memory T cells in preparation for a robust attack on second infection.
The production of naïve T cells by the thymus is highest at birth and during infancy, and accelerated reduction in thymic size and function is said to begin in the early 20s causing a high pool of old and exhausted memory T cells and low naïve cell census, thus leaving older people susceptible to infections and vaccination failure. However, few studies have now reported improvement in thymic size, with the increased production of naïve T cells among active older adults, in comparison to their sedentary counterparts. Interestingly, contracting muscles produce a special secretion called interleukin 7, which helps to bulk the size of the thymus and promote increase production of naïve T cells. Survival rates of naïve cells in blood circulation is also dependent on regular exercise via another muscular secretion called interleukin 15.
Frankly, “boosting” the immune system requires non-strenuous muscle contractions in form of regular exercise and thus promotes an anti-inflammatory environment. This sharpens the attack of immune cells and maintains the thymic production of battle-ready naïve T cell fighters against new invaders, with overall ability of older adults to withstand new infections and decrease vaccination failure. Who then says skeletal muscle is not an organ of immune system? Man is made to move, and importantly, regular activity is anti-inflammatory.
Keep moving, your immune competence depends on it.
Mukaila Kareem, a doctor of physiotherapy and physical activity advocate, writes from the USA and can be reached through email@example.com