The Important Role of NK Cells in Human Life

As human immunity increases with age, its changing trend is shown in the figure below.

After a newborn is separated from its mother, its immunity will temporarily decline. Later, it will mature under the induction of exposure to external antigens and other conditions, and its immunity will gradually increase. However, after a person reaches middle age, his immunity begins to gradually decline. The main reason for the reduced immunity of newborns is IgG. IgG is the only Ig class that can cross the placenta, and its transport process is active. Crossing of the placenta by large amounts of maternal IgG occurs late in pregnancy.

The newborn's own synthesis of IgG is slow, and serum IgG will drop to the lowest point 3 months after birth. By 10-12 months of age, all IgG in the body is produced by itself, and it reaches human levels at the age of 8-10 years.

After the age of 45, immune organs begin to age along with the human body, especially the thymus and other organs that severely atrophy. As the human body ages, the immune ability will undergo immunosenescence.

In terms of maintaining resistance to infection and tumors in newborns and the elderly, NK cells play a vital role when T cell function is incomplete or declining.

There is reason and evidence, and we speak with facts.

Stimulated by childbirth, the peripheral blood neutrophil count is high 12 hours after birth, gradually decreases after 72 hours, and then gradually rises to adult levels. The number of lymphocytes in newborns is small at birth, and exceeds the percentage of neutrophils at 6-7 months. The two are equivalent at 6-7 years old, and then gradually drop to low levels in old age as they grow older.

In addition, the development of neonatal monocytes has been perfected, but due to the lack of cofactors, their chemotaxis, adhesion, phagocytosis, oxidative sterilization, and production of G-CSF, IL-8, IL-6, IFN-γ, IL- 12 and antigen presentation abilities are worse than those of adults. Different types and doses of antigens or allergens exposed to neonates directly affect the immune regulatory function of monocytes/macrophages, especially DCs, and will affect the immune status of newborns in the future.

Compared with the longer development and maturation period of other immune cell subsets, NK activity can reach human levels 1-5 months after birth. ADCC function can reach adult levels at the age of 1 year.

Li Taisheng, director of the Department of Infectious Diseases at Peking Union Medical College Hospital, and others published an article " Aging of immune system: Immune signature from peripheral blood lymphocyte subsets in 1068 healthy adults" in the magazine "Aging" in May 2016 , analyzing the peripheral blood lymphocytes and their Changes in the number and proportion of factors in subpopulations with age. As shown below.

Statistics prove that among young people (19~44), middle-aged people (45~64), and old people (65~80), as age increases, the number of T cells that play cellular immune functions in specific immunity decreases. Or the functions are reduced to varying degrees ;

The number of B cells that exert humoral immune function generally remains stable. Among the innate immune core NK cell subpopulations, their number generally shows an increasing trend from young to old, and slightly decreases in middle-aged people; although the function of individual cells may decrease, the overall function remains stable.

It can be seen that NK cells play an irreplaceable role in maintaining the health of the elderly and maintaining anti-infection and anti-tumor functions .

Chi Xiaohua and others from the General Hospital of the People's Liberation Army discussed NK cells in a paper "Research Progress in Immune Cell Aging" published in the "Chinese Journal of Experimental Hematology" in 2012:

" The cytotoxic effects of NK cells play a major role in combating spontaneous, chemically induced, and viral infection-induced tumors. Studies have shown that both overall and relative numbers of circulating NK cells are elevated in healthy older adults compared with younger adults. " The age-related increase in NK cell numbers is thought to compensate for the reduced lytic capacity of individual cells ."

Shi Jinfang and others from the First Affiliated Hospital of Suzhou University discussed NK cells in the paper "Immunosenescence and Its Immunological Early Warning Indicators" published in "Modern Immunology" in 2005:

" Studies have shown that elderly people over 100 years old can also effectively fight infections because their NK cell system is fully functional and can migrate and effectively kill target cells. However, elderly people with damaged NK cells are prone to infections such as influenza and tuberculosis. Therefore, reduced NK cell activity is a precursor to disease, and maintaining NK cell activity can help extend life. "

Liu Zhonghui and others from Bethune Medical University (now Jilin University Bethune School of Medicine) published a paper "Age-related changes in T cell and NK cell activity in healthy people" in the "Journal of Gerontology" in 1992. The data is slightly different from the above conclusion, but it is also clear. Importance of NK cells.

Regarding T cells, the age-related T cell transformation activity and IL-2 secretion activity decreased with age, and were significantly correlated with age, with the largest decrease in activity in the 60-69 age group .

Regarding NK cells, NK cytotoxic activity also decreased significantly in the 60-69 age group, but then changed little and was not related to age.

"NK cells are a type of large granular lymphocyte, which is the first line of defense in the body's immune defense process. Its abnormalities are often related to the occurrence and development of malignant tumors. This study confirmed the activity of NK cells in healthy people of different ages . , cell activity decreased significantly at the age of 60 to 69 years, and subsequent changes had no obvious relationship with age . From an oncology perspective, the age at which tumors are most common is between 60 and 69 years old, and this result is consistent with changes in NK cell activity."

It can be seen that aging and abnormal cells are produced every day in the human body. Keeping the number and activity of NK cells normal can effectively resist infection and tumor occurrence.

Outlook

Now cell culture technology has enabled large-scale in vitro expansion of NK cells. In Japan, NK cell reinfusion has been normalized as an effective means of tumor treatment and anti-aging health care; in the United States, research on NK cells is in full swing; in China, NK cells have also embarked on the road to clinical research. NK cells will surely be more widely used in the fields of cancer prevention and anti-cancer in the future.