UCLA scientists have uncovered a harmful group of immune cells that quietly builds up in aging tissues and in the livers of people with fatty liver disease. When these cells were removed in mice, inflammation dropped sharply and liver damage was reversed, even though the animals continued eating an unhealthy diet. The research, published in Nature Aging , focuses on cellular senescence, a process triggered by stress in which cells stop dividing but do not die. These lingering cells, often called "zombie cells," remain active in tissues and release a steady stream of inflammatory signals that can damage surrounding cells. "Senescent cells are fairly rare, but think of them like a broken-down car on the 405," said Anthony Covarrubias, senior author of the study and a member of the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA. "Just one stalled car can back up traffic for miles. Now imagine five or ten of them slowly accumulating.…