NK cells are a type of lymphocyte or white blood cell and are part of your existing immune system. NK cells patrol your bloodstream looking for pathogens and unhealthy cells.  NK cells block the growth and spread of cancer through their ability to directly cause cellular cytotoxicity and death in cancer cells. Human NK cells normally constitute 5–15% of peripheral blood white blood cells. NK are also present in relative abundance in the bone marrow, liver, uterus, spleen and lung

The primary function of NK Cells in the body is the killing unhealthy and infected cells. The NK Cells also are responsible for detecting and controlling early signs of cancer. NK Cells are also found in the placenta and may play an Important role in pregnancy.

NK cells patrol the body and bloodstream looking for viruses, bacteria, foreign matter, and unhealthy cells. The NK cell’s job is to identify pathogens and signal other NK cells to gather around the pathogens. NK cells delver a toxic substance (cytokines and chemokines) directly to the pathogen or unhealthy cell. This toxic substance goes to work to penetrate the skin of the pathogen or unhealthy cell causing death. The NK cells release a hormone that will signal to other immune system cells, which then enter the area and dispose of the remains of the unhealthy cell.

With Age, NK cells produce less immune related secretions of cytokines and chemokines thus:

• NK Cells are less effective at killing cancer

• Less effective at deleting senescent(inactive) cells

• Less effective at fighting bacterial, viral and fungal infections

One study found older subjects had significantly lower numbers of total lymphocytes than younger subjects.  Also, NK cells of older subjects expressed higher levels of the aging markers meaning that they were not a vital as the NK from younger subjects. Older Subjects had lower baseline NK cell activity on a per cell basis than the young subjects. 

NK cells were identified over 40 years ago as special lymphocytes with innate ability to lyse tumor cells. NK cells can trigger target cancer cell death by releasing cytotoxins containing granzymes and perforin and through death receptor-mediated pathways. NK cells also play immunomodulatory functions by secreting chemokines and cytokines. Conventional NK cells are short-lived innate lymphocytes that lack antigen specificity which makes it difficult to target specific cancers.

An 11-year study of the Japanese general population, with rigorous use of various related biochemical and immunological markers, indicated that elevated cytotoxic activity of peripheral NK cells is positively associated with reduced cancer risk and vice versa, suggesting the certain importance of natural immune response toward tumors. Generally, NK Cells have proven more effective on blood malignancies and general prevention of cancer than for treatment of a specific cancer.

How do levels of existing levels of NK cells in the patient effect the formation of tumors. Several studies reported a higher incidence of cancers in individuals with defective NK cell function. in another study, mutant mice with impaired NK cell activity and mice treated with an NK cell-depleting antibody were reported to display higher rates of tumor growth and metastasis.  Many studies have since reported poor NK cell function in cancer patients, and case reports have been published on NK cell deficiencies that are characterized by an absence of NK cells or NK cell function or are caused by mutations of genes suggesting a link to higher rates of malignancy.   In mice, NK cells have been shown to control the growth and metastasis of transplantable tumors in studies based on the antibody-mediated depletion of NK cells.

The critical difference between NK cells and NKT cells is that NK cells are not antigen-specific receptors, while NKT cells are antigen-specific receptors.

Natural Killer T (NKT) cells are a unique subset of T cells. NKT cells have the capacity to mount strong anti-tumor responses and have thus become a major focus in the development of effective cancer immunotherapy. NKT cells can directly induce cell death in tumor cells and infected cells. NKT cells have been shown to play a critical role autoimmune disease, infection, transplant immunology, and cancer. Natural Killer T (NKT) cells are T lineage cells that share morphological and functional characteristics with both T cells and NK cells. Low numbers of NKT cells are found virtually everywhere T and NK cells are found such as in peripheral blood, spleen, liver, thymus, bone marrow and lymph nodes. Following their activation, NKT cells can immediately commence cytokine secretion without first having to differentiate into effector cells. 

The rapidity of their response makes NKT cells important players in the very first lines of innate defense against some types of bacterial and viral infections. NKT cells are mainly responsible for producing an immune response against pathogens and autoantigens (an antigen that is a normal bodily constituent). Also, they also participate in tumor rejection, control of autoimmune diseases, and immune surveillance. Based on the nature of the immune signal, NKT cells may produce either pro- or anti-inflammatory cytokines.

In cancer, NKT cells have attributed a role in immunosurveillance. In addition, in experimental models, NKT cells also act as potent activators of antitumor immunity when stimulated with a synthetic agonist.