The best offense is a good defense.

• Position: Bacteria - Defensins in the immune system

A small protein active in the human immune response can disable bacterial toxins by exploiting a property that makes the toxins effective--but also turns out to be a weakness. These toxins, which are released by bacteria, have malleable surfaces that allow them to move through porous areas of host cells to pave the way for bacteria to stay alive, but that same malleability makes the toxins vulnerable to these immune system proteins, which bind to the toxins and render them useless.

The small proteins are called defensins and are peptides made up of about 30 amino acids. Scientists have known for about a decade that defensins can neutralize bacterial toxins but, until now, did not know how. Though the researchers used a single defensin for most of their experiments, their work with a handful of others suggests that all defensins are similar enough to share this capability. This makes defensins a potentially promising model for the development of drugs that could mimic their activity and reduce pathogens' infectious power.

"An important part of our findings is that the defensin offers universal protection. Not every single toxin will be affected, but many toxins will," says Dmitri Kudryashov, assistant professor of chemistry and biochemistry at Ohio State University, Columbus, and senior author of the study. 'They are less potent than an acquired antibody response, but that response takes time. So, when the body meets a pathogen for the first time, defensins provide a less efficient--but universal--defense. This is what gives them their strength."

Defensins are part of the innate immune...