Is there any measureable indicator and reference for “aging”? A team led by Professor Li Taisheng from the Department of Infectious Disease, PUMCH spent ten years on a large-scale research on the immune functions of healthy groups and was the world’s first to reveal the normal scopes and changing trends of immune indicators of healthy people (i.e. lymphocyte subsets in peripheral blood) in different age groups. The result was published in Aging, the journal of world No. 1 impact factor in the field of aging, and was recognized as another important application of lymphocyte subsets research in the field of human health.
According to the research, as age grows, there is no obvious fluctuation in human B cells and NK cells. The total number of T lymphocyte drops from 1403 to 1198 units, meaning a decline in immune functions. There is no great change in the total number of CD4, and the average level in young, middle and old age groups is 690, 708, 698 respectively. However, the two armies under CD4 command, “active forces”--memory cell, and “militia and reserve”--naive cell, showed a remarkable trend of wane and wax in their total numbers. Specifically, the average level of naïve cells in young, middle and old age groups is 271, 249 and 226, whereas the levels of memory cells are 419, 459 and 472 units.
According to the data, it is surmised that as the body ages, more naïve cells are mobilized to form memory cells, so that naïve cells decrease and memory cells increase in number. This partly explains why an infection, once occurred in an old-aged person, is hard to control--because of the lack of naïve cell reserve. Therefore the possession of more naïve cells than same-age groups means higher “immune reserve” and a slowdown of the aging of immune system.
When the body is infected by pathogens, the antigen-presenting cells in human lymphocytes will, through an important co-receptor called CD28, send warning to CD4, then CD4 will go to perform a “bombing”. According to the research, CD28 decreases as age grows, causing a decline in signal transmission; as a result, lymphocytes are unable to detect and clean out pathogens quickly, and the body suffers declined pathogens-resisting capability. This explains why vaccination in old-age groups is of less desirable effects.
Given the absence of international related researches on lymphocyte subsets in healthy groups, Professor Li’s research is of great significance in establishing the reference scopes of lymphocyte subsets in healthy groups and the probing into aging mechanisms at cell level. According to Li, in the result sheet of blood routine examination currently in clinical use, the normal scope of lymphocytes is an average regardless of age. For example, the application of old references will obviously “underestimate” the immune functions of old-age groups. The reference scopes for different age groups of healthy people arising from this research will lead to more precision in clinical assessment of human immune functions.