Much like humans generate mountains of garbage, our cells are constantly discarding proteins that are damaged or no longer needed. The cellular waste disposal system called the proteasome is best known for its central role in protein degradation and recycling, but as far back as the 1990s it was shown that products of this process – short protein sequences called peptides – can be displayed on the cell surfaces, helping the immune system to identify threats. In a new study published today in Nature, Prof. Yifat Merbl’s lab at the Weizmann Institute of Science reports uncovering a surprising immune mechanism involving the proteasome. The team discovered that some of the peptides released in the proteasome during protein breakdown are capable of killing bacteria. These findings expand our understanding of the body’s innate defenses and offer new hope for tackling the growing threat of antibiotic resistance.