Is Exercise really beneficial? Demystifying the myth with Flow Cytometry – CD56+ Natural Killer Cells

Exercise, get moving, get fit, get healthy! Its been a common theme to see posters published by health promotion board everywhere to promote exercising and leading an active lifestyle to prevent cancer. Pfff… Why exercise? Aint no body got time for that. You might change your mind after reading this article.  
Health authorities and practitioners have always vehemently advocated that regular exercise reduces the risk of cancer and metabolic diseases. However, immunological mechanisms linking exercise and reduced cancer risk are limited 

Here in this article, we would look at a small study done in Murdoch University ^[1], published in 2016 to highlight a few key aspects on how exercise can influence the immune system to potentially contribute to cancer prevention. 

Figure 1: Exercise ellict a bi-phasic response where there is a significant increase in numbers in all lymphocyte groups and a subsequent reduction in the recovery phase.

Simplistically, Figure 1 effectively demonstrated that exercise can trigger a transient bi-phasic response where there is a significant mobilisation of different types of crucial lymphocytes; Natural Killer (NK CD56+) cells, T- (CD3+) and B- (CD19+) lymphocytes into the circulating blood, and then significantly fall in numbers during recovery. This bi-phasic phenomenon has been well documented by multiple studies. Furthermore, as observed in the diagram, the NK cell population is most responsive to an acute bout of exercise. Therefore, this article will focus on the NK cells and how they can potentially contribute to cancer prevention and management.

Figure 2: NK cells are part of the WBC population as seen in the first dot plot diagram, using CD45 as a “mature-cell” marker, we can then select the lymphocyte population as CIRCLED in red. With literature knowledge that NK cells do not express CD14, CD3, CD19, CD20, we can then use the third diagram to NEGATIVELY select the desired population. Subsequently in the final plot we can then further classify the NK cells into their respective subpopulations (CD56^dimCD16+ & CD56^brightCD16- NK cells)

NK cells are a critical component of the innate arm of the immune system that are able to recognize and eradicate tumor cells without prior antigenic exposure. Phenotypically in flow cytometry terms, they are part of a lymphocyte group that specifically express the CD56 marker and can be classified into CD56^dim and CD56^bright. In the human body, CD56^bright NK cells resides in the secondary lymphoid organs such as lymph nodes and tonsils, whereas the CD56^dim NK cells resides in the spleen and blood circulation. Immunologically, the CD56^dim population is considered the most mature form of all NK cell variants and has the most tenacious cytotoxicity effect against tumour cells. Moreover, multiple exercise immunology research studies have unanimously demonstrated that the CD56^dim NK cells is the most responsive to an acute bout of exercise compared to all other lymphocyte cell types.

An intriguing study done by a group of Danish researchers found that mice who spend more time on a running wheel has their tumors shrunk by 60% compared to their more sedentary mates ^[2]. Physiologically, a high level of adrenaline and a cytokine known as Interleukin-6 (IL-6) is released into the blood circulation during exercise. Moreover, the researchers also found that adrenaline specifically recruits IL-6 sensitive NK cells and the IL-6 cytokine facilitate attraction of the NK cells to the tumors. Besides that, there is an enhanced expression of NK cell-related activating receptors, stimulatory cytokines and chemokines in the tumors of running mice. Hence the authors suggested that exercise also support the establishment of a tumor microenvironment that is more prone to NK cells activation and consequently promote NK cell cytotoxic destruction of the tumour cells.

This research is hopeful for cancer patients as it provides an inexpensive way to keep their tumor under control. However, some questions remain to be explored, including whether this observation also hold true in humans, or how effective it will be when combined treatment with chemotherapy is carried out in patients.

In conclusion, prevention is better than cure. Exercising is such an economical accessible way to prevent cancer. There is not much negative implications or risks in exercising, but there is a whole world of beneficial health impacts. Most importantly, health is wealth, we should heed the aforementioned advice and take time out regularly to get a bout of moderate intensity exercise. As always, stay fit, stay healthy!

References

1. Preferential Mobilization and Egress of Type 1 and Type 3 Innate Lymphocytes in Response to Exercise and Hypoxia. Ng Ivan, Fairchild Timothy, Greene Wayne and Hoyne Gerard. Immunome Research 2016.
2.  Voluntary Running Suppresses Tumor Growth through Epinephrine- and IL-6-Dependent NK Cell Mobilization and Redistribution. Line Pedersen, Manja Idorn, Gitte H. Olofsson, Britt Lauenborg, Intawat Nookaew, Rasmus Hvass Hansen, Helle Hjorth Johannesen, Ju¨ rgen C. Becker, Katrine S. Pedersen, Christine Dethlefsen, Jens Nielsen, Julie Gehl, Bente K. Pedersen, Per thor Straten and Pernille Hojman. Cell Metabolism 2016.

Disclaimer

• Flow cytometric analysis images depicted in this article are for simplified illustration purposes only and shall not constitute to the exact analysis process.
• Information provided are for informal reading and not for official research usage