Published July 6 2015
Natural killer cells are a type of white blood cell, which in turn is part of the innate immune system. They serve numerous functions, but one of the most important roles is to control certain types of microbial infections, such as mycobacterium tuberculosis, certain viruses, etc. They also play a role in controlling the growth of tumors. And as you might have guessed, they also can play a role in thyroid health, especially with regards to autoimmune thyroid conditions such as Graves’ Disease and Hashimoto’s Thyroiditis.
The innate immune system is the first line of defense when someone has any type of infection. There are numerous cells involved in this process, which include macrophages, neutrophils, eosinophils, basophils, dendritic cells, and natural killer cells. All of these cells play an important role, as neutrophils are phagocytic cells which clean up debris and also release chemicals which attract other types of white blood cells. Basophils are involved in the release of histamine. Dendritic cells are involved in something called antigen presentation. An antigen is a foreign substance (i.e. bacteria, toxins), and with antigen presentation, dendritic cells bind to these antigens and present them to the immune system.
As for natural killer cells, in the opening paragraph I mentioned how these control certain infections and the growth of tumors. However, they don’t do this by directly attacking the bacteria, microbe, or tumor, but they instead destroy cells of the body that have been compromised by these infections or tumors. It’s pretty amazing when you think about it, as the natural killer cells have the intelligence to not to attack the normal cells of the body.
What Role Do Natural Killer Cells Play In Autoimmunity?
In the past I put together a blog post entitled “The Role of Cytokines In Autoimmune Thyroid Conditions “. Cytokines are present in autoimmune conditions such as Graves’ Disease and Hashimoto’s Thyroiditis, and in the blog post I discussed how cytokines are “regulators of host responses to infection, immune responses, inflammation, and trauma”. I also mentioned how dysregulation of cytokine production can play a big role in the development of autoimmune thyroid conditions. The dysregulation of cytokines leads to the chronic activation of something called nuclear factor kappa B (NF-kB), and so one of the main goals of a natural treatment protocol is to do things to downregulate NF-kB.
But what does this have to do with natural killer cells? Well, natural killer cells can be activated to produce high levels of certain cytokines (1) . For example, in patients with allergic diseases, natural killer cells are involved in the production of Th2 cytokines, which in turn contributes to the immune system imbalance (2) . Natural killer cell overactivation can be found in patients with conditions such as alopecia areata and pemphigus vulgaris (2) . In addition, cytokines such as interleukin (IL)-2, IL-12, IL-15, IL-18, IL-21, and type I interferons are very important factors involved in the maturation, activation, and survival of natural killer cells (3) . What’s important to understand is that dysregulation of the immune system is characterized by an increase in pro-inflammatory cytokines and natural killer cell activation.
There have been a few studies looking at natural killer cells in people with autoimmune thyroid conditions. One study examined the changes in the activity and number of natural killer cells in patients with autoimmune thyroid conditions (4) . The results of the study indicated that an increase of natural killer cell activity is associated with a worsening of autoimmune thyroid disease both in Hashimoto’s Thyroiditis and Graves’ Disease, and suggests that natural killer cells might have an important role for the control of disease activity in autoimmune thyroid conditions (4) . However, another study looked at natural killer cell activity in patients with Graves’ Disease and Hashimoto’s Thyroiditis (5) , and showed that natural killer cell activity in patients with Graves’ disease did not correlate with serum levels of thyroxine, the presence or severity of ophthalmopathy, or titers of serum thyroid antibodies. According to the same study, in patients with Hashimoto’s Thyroiditis there was no correlation between natural killer cell activity and goiter size, titers of antibodies, or thyroid status (5) .
Other studies have showed a possible association between decreased natural killer cell numbers and thyroid autoimmunity (6)  (7) . The correlation of decreased natural killer cell numbers and/or function with autoimmune diseases raises the possibility that autoimmunity may arise from natural killer cell deficiencies (8) . However, this hasn’t been proven yet, and more research needs to be conducted in this area.
Can Natural Treatment Methods Modulate Natural Killer Cells?
In my blog post where I spoke about proinflammatory cytokines I discussed how certain nutrients and herbs can decrease pro-inflammatory cytokines and inhibit NF-kappa B, which in turn can help suppress the autoimmune component (assuming the autoimmune trigger has been removed). And so after reading this information you might wonder whether certain nutrients and herbs can help to modulate natural killer cells? The answer is “yes”, but a better question to ask might be “SHOULD nutrients and herbs be used to modulate natural killer cells?”
For example, studies show that the herb echinacea can increase natural killer cells (9)  (10) . However, some studies show that echinacea and other immunostimulatory herbal supplements can either cause or exacerbate autoimmunity (11) . But earlier I also provided some evidence that decreased natural killer cells are common in autoimmune thyroid conditions. It can get confusing, but remember that pro-inflammatory cytokines are involved in autoimmunity, and natural killer cells can increase these cytokines. And so when you look at it from this perspective hopefully it makes sense as to how natural killer cells can trigger or worsen autoimmunity by increasing pro-inflammatory cytokines.
However, remember that natural killer cells play a role in combating certain pathogens, such as viruses. As a result, if someone has low natural killer cells then this can make the person more susceptible to an infection, thus setting the stage for autoimmunity. And so while someone with Graves’ Disease or Hashimoto’s Thyroiditis shouldn’t intentionally take supplements and herbs to increase natural killer cells, they also don’t want these levels to be too low. Taking nutrients and herbs to decrease pro-inflammatory cytokines will decrease natural killer cells to some extent, although it shouldn’t cause them to be depressed.
So unlike pro-inflammatory cytokines, I don’t specifically recommend for people to do anything to directly increase or decrease natural killer cells. However, I do recommend for my patients to do things to reduce pro-inflammatory cytokines, which in turn will also decrease natural killer cells. In my blog post on cytokines I discuss some things you can do to reduce these.
In summary, natural killer cells help to control certain infections, as well as the growth of tumors. Some studies show that an increase in natural killer cell activity can worsen Graves’ Disease and Hashimoto’s Thyroiditis. However, other studies show an association between decreased natural killer cells and thyroid autoimmunity. Overall the goal shouldn’t be to increase or decrease natural killer cells, but to do things to reduce pro-inflammatory cytokines and improve the overall health of your immune system.