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Aging turns lymph nodes into fat, impairing immunity

Lymph nodes usually serve as the headquarters of our immune system. When we are vaccinated or get an infection, these nodes are the sites at which immune cells congregate, activate, and proliferate in order to mobilize an effective immune defense. However, with age, the normal tissue in the lymph nodes (called “the stroma”) is gradually replaced by adipose tissue (fat), in a phenomenon known as lipomatosis. Although this phenomenon is quite common and increases with age, relatively few scientific studies have addressed it to date.

Now, by analyzing over 200 lymph nodes, a team of researchers from Uppsala University in Sweden has found that lipomatosis begins in the medulla (the central part of the lymph nodes), and is characterized by the transformation of the fibroblasts (the supporting parts of the lymph nodes) into adipocytes (fat cells). In addition, some specific types of fibroblasts located in the medulla seem to be more prone to become adipocytes.

According to the scientists, in the early stages of lipomatosis, changes arise which impair the ability of lymph nodes to provide effective immunity. For instance, the specialized blood and lymphatic vessels that are normally used channels for immune cells to enter and exit the lymph nodes are destroyed in the areas of the nodes where fat has formed. Thus, lipomatosis may be a critical factor why many elderly people get more severe infections or have poorer responses to vaccination.

“Our study is a first step towards understanding why lipomatosis occur, and towards the longer term goal of finding ways to prevent its progression and the destruction of the lymph node,” said study lead author Tove Bekkhus, an expert in Immunology, Genetics, and Pathology at Uppsala.

Since the researchers are currently unable to mimic the effects they observed in human lymph nodes in animal models normally used for the study of aging, direct analyses of human subjects is necessary. 

“I hope our work will spur an interest among other researchers in including lymph nodes lipomatosis as a factor when studying elderly people’s responses to vaccination and infections. The changes we observe are also highly relevant to cancer research, since in several types of cancer, the lymph nodes are the first places cancer cells spread to,” said study senior author Maria Ulvmar, a professor of Medical Biochemistry and Microbiology at the same university.

“Our publication provides the first chapter of a story about fat and loss of function in our lymph nodes when we age. We will now continue to develop this story by designing new studies to learn more about the underlying causes and consequences of these changes.”

The study is published in the Journal of Pathology.  

By Andrei Ionescu, Staff Writer

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