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Naive T-Cells Decline with Age

AIM which works within IBS (the Institute for Basic Science) released a paper containing the details explaining a problem that is known to immunologists for many years, what is the cause of the decline in immunity when a person gets older. Everyone’s immune system declines gradually, and it is no longer able to create an immune response to fight pathogens. Only 17 – 53% of flu vaccinations are effective in people who are 60 and over where the stats show that people who are younger are effective from between 70 and 90%. What is the reason for this?

T cells: Function and destiny

T cells are very important for effective immunity in the human body, and there are two broad types that exist. Naïve T are the new recruits meaning they have not fought or been exposed to pathogens but are diversified and provide cover against infectious agents. The memory T cells are slightly less diverse but are experts, hardened and scarred from fighting malicious invaders. When puberty begins, the naïve T cells start to disappear, rendering those individuals who are older vulnerable to infections especially with new pathogens that were not triggered in the memory cells. The most popular view used to explain why there is a loss of naïve T cells is due to the decreased production of any new T cells in the thymus as well as the natural conversion of naïve cells into memory cells. The thymus will continue to produces lower than normal levels of naïve T cells as people get older. The positive side is that those T cells do have a longer lifespan. Then what is the reason?

Naive T-Cells

The director of AIM, Charles Surh, and his research team set out to answer this question. Looking at the lymph nodes, they found deterioration in the stromal cells population. Static cells are imperative in ensuring the survival of the naïve T cells while also maintaining the lymph node structure. Surh stated that this theory had not been investigated before. They looked at the stromal cell population defect contributed to the T cell loss within the lymph node. He advised that this defect could only be rectified before the cells can be replaced.

The team set a number of experiments in place to test the hypothesis. Mice with lower white blood cells were tested to see if they could support the natural proliferation of the mature T cells. The team believed that these approaches to be a way to determine the factors that allow the naïve T cells survive. The factors found declined in middle-aged mice and more so in older mice. Extra naïve T cells were delivered to the older mice, but this did not have any influence as they dissipated before two weeks while lasted longer in the younger mice. The hypothesis looked promising and proved that aging influences the environment for T cell survival. The focus was changed to the population in the lymph nodes of the stromal cells.

Problem-solving at AIM

The results of the experiment supported the theory of the team. Their work showed that the lower naïve T cells in old age are not due to the decline in their production only but also from the deterioration in their environment that is supposed to support their survival.