UCLA researchers discover "zombie" immune cells driving chronic liver disease and metabolic aging

UCLA scientists find that clearing senescent immune cells can reverse fatty liver damage, offering a new path for treating age-related metabolic conditions.

By: AXL Media

Published: Apr 16, 2026, 7:51 AM EDT

Source: Information for this report was sourced from University of California - Los Angeles Health Sciences

The Discovery of Pathological Immune Cell Persistence

Researchers at the University of California, Los Angeles, have pinpointed a rogue group of immune cells, described as "zombie cells," that appear to be a primary catalyst for fatty liver disease and age-related inflammation. These cells, formally known as senescent macrophages, undergo a stress response where they cease to divide but remain biologically active within the tissue. According to Anthony Covarrubias, an assistant professor and senior author of the study, these cells act like a stalled vehicle on a crowded highway, where even a small number can create massive disruptions by secreting a toxic mixture of inflammatory signals that damage surrounding healthy areas.

Decoding the Molecular Signature of Senescence

For a long period, the scientific community remained divided on whether macrophages could truly become senescent, as these patrolling immune cells often naturally display markers that mimic cellular aging. The UCLA team overcame this hurdle by identifying a unique molecular fingerprint consisting of two specific proteins, p21 and TREM2. When found in combination, these markers accurately identify macrophages that are no longer functional but continue to inflame the liver. Using this diagnostic tool, investigators observed that senescent macrophages in the liver rise from a mere 5% in young subjects to as high as 80% in older ones, providing a direct link between these cells and the biological process of aging.

Cholesterol as a Catalyst for Cellular Decay

The research highlights that chronological aging is not the only factor triggering this cellular transformation, as excess cholesterol was found to be a major driver of the condition. In laboratory settings, healthy macrophages exposed to high levels of LDL cholesterol rapidly developed the hallmarks of senescence, adopting the p21-TREM2 signature and ceasing normal division. Ivan Salladay-Perez, the first author of the study, noted that while macrophages are naturally equipped to handle cholesterol metabolism, a chronic state of overnutrition creates a pathological environment. This suggests that high-fat diets may effectively accelerate the biological aging of the liver and other vital organs by forcing immune cells into this dysfunctional state.