A young immune system fights aging

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Carolina Florian of the Bellvitge Institute for Biomedical Research in Barcelona, ​​Spain, recently discovered that the old mice in the laboratory began to look younger and more lively. However, Florian only briefly treated them with a drug a few weeks ago that corrects a protein organization in stem cells. The relevant research paper was recently published in the internationally renowned academic journal Nature.

The human immune system is a complex system with numerous cellular and molecular components working together to shape development, defend against infection, help wound healing, and eliminate cells that may become cancerous. But as we age, the composition of the human immune system begins to change and becomes less effective. In old age, the human body becomes susceptible to a variety of infectious and non-infectious diseases, and more resistant to the protective effects of vaccines.

Florian's magic bullet targets the immune system. The stem cells she treats are called hematopoietic stem cells, which can differentiate into all immune cells. As they circulate in the blood, these immune cells infiltrate every organ and affect all functions of the body.

Hematopoietic stem cells in the bone marrow give rise to two branches of immune cells, which differentiate into two major categories: lymphoid and myeloid. These two major categories of cells further differentiate, with lymphoid cells primarily responsible for adaptive immunity, including B cells that produce antibodies, T cells that help attack invaders and coordinate complex immune responses, and natural killer cells that destroy infected cells. Myeloid cells include a variety of cell types that are primarily involved in innate immunity.

As we age, one of the earliest changes in our immune system is the shrinkage of the thymus gland, which begins after puberty. This organ is home to T cells, and by the mid-30s, much of the tissue has turned into fat, which greatly reduces the production of new T cells and weakens the immune system. More importantly, as T cells age, their ability to recognize infectious agents becomes less specialized.

The ratio of different types of immune cells in the blood was also changing. The ratio of myeloid cells to lymphoid cells was heavily weighted toward myeloid cells, which could trigger inflammation. In addition, more immune cells became senescent, meaning they stopped replicating without dying.

Any cell in the body can become senescent when it becomes damaged by mutation, and once in this state, the cell begins to secrete inflammatory signals, marking itself for removal. This is an important anti-cancer and wound healing mechanism that works well when we are young, but as we age, too much damage accumulates and the body's immune cells themselves become senescent. Senescent immune cells, attracted by inflammatory signals, secrete their own inflammatory molecules, which not only fail to clean up properly, but also increase inflammation that damages surrounding healthy tissue. This phenomenon is called "inflammaging."

The molecular makeup of blood stem cells changes with age, which throws off the balance in how they produce immune cells. Florian says that fixing this imbalance that occurs over time appears to be a solution to many aging problems, not just in the immune system but elsewhere in the body.

Other scientists have come to the same conclusion using different experimental methods:

Rejuvenating the immune system can rejuvenate many organs in animals, at least in mice, and there is evidence that aging of the immune system may actually drive aging in these organs.

The goal of helping people stay healthy in their later years is tempting, but translating this knowledge into clinical applications is challenging. Researchers caution that interfering with the highly complex immune system can be dangerous, so they decided to start with low-risk targets, such as improving the response of the elderly to vaccinations and increasing the efficiency of cancer immunotherapy. Sebastiano, a stem cell scientist at the Stanford School of Medicine in California, said that while reversing immune aging may hold promise for controlling age-related diseases, it is still necessary to explore with caution.

(The author is a member of Anhui Science Writers Association)