Macrophages, which hoover up pathogens, have been implicated in the chronic inflammation that sets in with the march of time.Credit: Science Photo Library
A newly discovered type of immune cell found in fat tissue seems to contribute to the chronic inflammation associated with ageing, according to preliminary data from mice — but other immune cells in fat help to keep inflammation at bay1.
The inflammation-promoting cells emerge only in older mice, researchers found. Although the cells’ precise role is unclear, they display several signatures associated with ‘inflammageing’ — the persistent inflammation that develops as people grow older. The findings were published on 2 September in Nature Aging.
“We did not anticipate that there would be a completely new cell type,” says study co-author Vishwa Deep Dixit, an immunobiologist at Yale University in New Haven, Connecticut.
Inflammation age
When injuries or infections occur, the immune system mounts a protective response by releasing cells and proteins to affected tissues. This complex cascade is called inflammation. But as we age, inflammation gradually increases and becomes persistent instead of being a state that occurs only when things go wrong.
Ageing is linked to inflammation — but only in the industrialized world
Among the cells that that help to regulate this inflammageing are a variety of macrophages — white blood cells that hoover up pathogens and cellular debris — that reside in fat tissue. But the exact roles of each type of macrophage and how these cells change throughout the ageing process remain a mystery, says study co-author Elsie Gonzalez-Hurtado, also an immunobiologist at Yale University. “There wasn’t really a good characterization of these cells.”
To build a clearer picture, Gonzalez-Hurtado and her colleagues imaged macrophages in the visceral fat, the deep fat that wraps around the organs, of young and aged mice. The researchers sorted the macrophages into categories on the basis of the cells’ RNA molecules. These molecules indicate which genes in a cell are active, and therefore offer a guide to the cell’s function.
Multitude of macrophages
The results revealed 13 distinct types of visceral-fat macrophage, some of which varied in abundance with age. A previously known type of macrophage that resides near nerves, for example, became less numerous in female mice as they grew older — but its numbers remained constant in males. Another previously known type of macrophage, which congregates near fat-tissue blood vessels, was less numerous in elderly male mice than in younger ones, but its levels did not vary with age in female mice.
