Nature Communications: Immune Cells Have an Inbuilt Satiety Sensor

These cells patrol the body, consuming unwanted material such as bacteria, fragments of damaged tissue, and millions of the body’s own cells that undergo programmed cell death during organ growth and renewal. Macrophages begin to engulf their targets only after detecting specific markers on their surfaces. Cells that ingest too much become less mobile and less effective at fighting infections, making a strict appetite-control mechanism essential.

The researchers suspected that the nucleus might play this role. It is the cell’s largest and stiffest structure, approximately ten times stiffer than the cytoplasm, and it houses the DNA. By observing macrophages in fruit fly embryos in real time, the scientists found that an ingested particle could reach the nucleus within just two minutes and push into it. At least one such indentation was observed in 88% of cells carrying ingested material.

In response, the nucleus built up a layer of the protein lamin B beneath its membrane. Lamin B acts as both a structural scaffold and a spring: the more actively a cell engulfed material, the thicker this layer became.

To test the nucleus’s role, the researchers separately switched off the gene encoding lamin B and disrupted a bundle of protein cables connecting the nucleus to the cell’s internal skeleton. Without these proteins, the macrophages’ appetite dropped sharply: they engulfed fewer particles, and the particles were noticeably smaller. By contrast, in cells with excess lamin B, the engulfed material was larger. These findings confirmed that the satiety signal originates in the nucleus.

“The molecular and mechanical remodeling of the nucleus in response to ingested particles is critical for macrophages to continue clearing dying cells,” the study authors emphasize.

Scientists have been searching for a mechanism that limits macrophage appetite for more than 30 years. Until now, the only confirmed limiting factor was the supply of membrane that the cells use to wrap around each new portion of material. The newly identified mechanism adds a mechanical satiety counter to this process, and it appears to be evolutionarily ancient. In mice, ingested material also deforms macrophage nuclei, while levels of a related lamin protein increase as the cells engulf their targets.

Overloaded macrophages contribute to the development of atherosclerosis and can interfere with wound healing. Pharmaceutical researchers are also increasingly exploring these cells as potential drug targets. If scientists learn how to regulate macrophage satiety, they may eventually be able to make the body’s cellular cleanup crew work more effectively in damaged blood vessels.