Homegrown Defender: Urinary Infections Face Natural Guard

Article excerpt

Bacteria are adept at sneaking past our defenses, succeeding most often when swallowed, inhaled, or given free passage via a cut or scratch. But over the past 2 decades, scientists have found that even before the immune system can gin up a response to such intruders, built-in antimicrobial agents in the intestines, lungs, and skin act as a first line of defense. A new study shows that one of these antimicrobial shock troops, a peptide called cathelicidin, patrols another portal as well--the urinary tract.

Cells that line the urinary tract all the way back to the kidneys churn out cathelicidin in response to bacterial invaders, researchers report in the June Nature Medicine. Furthermore, inflammatory cells later deliver a second dose of the antimicrobial peptide to those passages, the scientists say. By damaging the bacterial membrane, cathelicidin usually kills a microbe on contact.

Cells lining the urinary tract normally keep a small supply of cathelicidin on hand, and they crank out more within minutes of contacting bacteria, report Annelie Brauner, a physician and microbiologist at Karolinska

University Hospital in Stockholm, and her colleagues. While urine samples obtained from 28 healthy children contained modest amounts of cathelicidin, samples from 29 children with urinary infections caused by bacteria harbored eight times as much of the peptide, the researchers report.

In a series of experiments, the researchers introduced Escherichia coli, which causes urinary tract infections, into the urethras of mice. The bacteria reached the bladder in greater numbers in animals genetically engineered to lack cathelicidin than they did in normal mice. Animals that lacked the peptide also developed more full-blown infections, lost more weight, and were more likely to die. …