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What Are Natural Killer Cells?

Natural killer cells (also called NK cells or K cells) are a type of lymphocyte, or white blood cell, found in the human immune system. They are a crucial component of our innate immune response, acting as the front line of defence against invasion by foreign bodies. NK cells are usually deployed to eradicate virally infected cells, but they are also crucial in detecting and destroying early malformations in cell production, which we know as cancer. Cancer is not something you can catch like an infection; it starts within our bodies when they malfunction. NK cells are therefore extremely valuable, and we rely on them daily to keep us healthy. Yet for all their importance, relatively few people know exactly what they are, or what they do. 

The human body has two immune systems: the innate and the adaptive. The innate is the dominant system found in many forms of life, and is suspected to date back millions of years. This is where natural killer cells are found. They have similar properties to T cells, another crucial component of our immune system, but are unique in that they have a broader role in defence – hunting down and killing stressed cells before they can do damage. In contrast, T cells focus entirely on hunting down one type of cell and eradicating it. In addition, some recent studies have postulated that NK cells are even more important than we first believed, and that they may cross over to the adaptive immune system, performing important functions there as well. While research is still being undertaken in this area, it could lead to significant breakthroughs in the way specialists approach cancer treatment.


Further research on natural killer cells could lead to significant breakthroughs.


The activity of natural killer cells can be likened to a police officer or security guard. They ‘patrol’ the body, always on the lookout for suspicious activity within the system. While out on these patrols, they are in constant communication with cells they encounter. If their receptors are triggered by an irregularity or imbalance, they will destroy the cell in question. Most normal cells present with MHC class I (major histocompatibility complex), which identifies the cells as ‘self’; NK cells are designed to recognise this molecule, and will ‘switch off’ their attack if they sense it. Cancer and infected cells will often shed their MHC-I, which makes it easy for the NK cells to seek them out and destroy them. Both the MHC-I genes and the corresponding receptors vary greatly between individuals.

When it comes to chronic disease, a compromised immune system is usually one of the constant factors patients must deal with. In the case of chronic Lyme disease, natural killer cells have become a major bone of contention. On one hand, the chronic spread of the disease would suggest that these cells are not doing their job properly, or are even absent entirely. This is why the bacteria is allowed to run free within the body, leading to excessive symptoms that are hard to treat. However, this is not actually the case; it remains one of the primary misunderstandings many patients and doctors have about Lyme disease. In fact, many of the symptoms of chronic Lyme are caused by an overactive immune system, which acts hyper-aggressively. This leads to joint pain, swelling, aches and a constant sense of fatigue, as well as potentially more specific symptoms like neurological complications and cardiac issues.


Research is being conducted into the role of natural killer cells in Lyme disease.


A study from 2013 that set out to determine NK cell activity in Lyme-based arthritis patients produced some interesting results. Patients with antibiotic-refractory arthritis (i.e. arthritis that did not respond to antibiotics) showed high numbers of natural killer cells, even after spirochetal (bacterial) killing, ultimately suggesting that these cells contributed to excessive inflammation and immune dysregulation in joints. Essentially, even after the initial infection had been eradicated, the NK cells continued to react, leading to a whole set of debilitating symptoms for patients. In addition, invariant natural killer T cells (iNKT cells for short), which may have immunomodulatory properties, were found to be absent in antibiotic-refractory patients. This would further compound the effects of the aggressive NK cells. Though this particular study was limited to arthritic symptoms, the potential extent of the damage caused by NK cells in Lyme disease patients remains largely obscured.

BCA-clinic in Augsburg are specialists when it comes to Lyme disease. They know the difference between the infection and inflammation stages of the disease and how to treat patients accordingly. Their research into how exactly NK cells affect Lyme patients is paramount, as we’re still in the dark about so much of the disease. Indeed, chronic Lyme is not even fully recognised as a legitimate disorder in many places, despite thousands of patients suffering from it. Natural killer cells and how they react to the Lyme infection are only one facet of the problem, but finding out more about the details of this process would undoubtedly be a valuable step in countering the manifold issues surrounding the disease.