Immunosenescence is a deterioration of the immune system that occurs with age. When older mice are subjected to fasting, cells of the immune system such as lymphocytes return to quantities more typical in youth. This animal research may have implications for human aging. In this clip, Dr. Valter Longo describes how fasting promotes the immune system to return to a more youthful profile.

Rhonda: Mm-hmm. This seems like it has, I mean, implications for human aging because, you know, if you're talking about humans as we age, something occurs called immunosenescence, where we start to lose some of our, you know... We don't we don't make as many lymphocytes, actually, it's the lymphoid population that decreases with age. And so, if you're able to then be able to activate these hematopoietic stem cells to regenerate, you know, the blood cell population, that seems like it would have implications for aging. But, also, I thought you found something very interesting in that paper, and that was what we talked about with the regenerating the hematopoietic stem cells, which also increased in cell number if I remember correctly.

Valter: Mm-hmm.

Rhonda: You also did this experiment in older mice, and you showed something very interesting, I thought because as we age, the immunosenescence seems to be happening. And I may be doing a huge oversimplification here, but it seems to be happening in the lymphoid cells, which are mostly B and T cells as opposed to the other blood cells we have, the myeloid lineages, which are composed of neutrophils, macrophages, platelets, and things like monocytes. So, as we age, we have more of those types of immune cells. But you actually found that if you fasted those animals, something happened with their populations, correct?

Valter: Yes, so we found that the lymphocytes number goes back to the more youthful level, and the ratio of myeloid cells to lymphocytes because they're also back not to the same level as during youth, but certainly it moves in that direction. And so, the profile of the immune system is much more similar to the young one, so essentially, we see a rejuvenation of the system.