Bacteria Shuts Down Immune System in Newborns
Reported July 16, 2009
(Ivanhoe Newswire) — Group B Streptococcus (GBS), a bacterial pathogen that causes sepsis and meningitis in newborn infants, is able to shut down immune cells in order to promote its own survival, according to researchers at the University of California, San Diego (UCSD) School of Medicine and the Skaggs School of Pharmacy and Pharmaceutical Sciences. Their study offers insight that may lead to new medical therapies for invasive infectious diseases that affect nearly 3,500 newborns in the United States each year.
Approximately 20 to 25 percent of women of childbearing age are asymptomatic carriers of GBS on their vaginal mucosal surface. Newborns can become infected with GBS that invades through the placenta to initiate infection in the womb, or during delivery by exposure to contaminated vaginal fluids. Screening of pregnant women for GBS and antibiotic prophylaxis during labor is used to reduce the risk of transmission, yet it is estimated that approximately 3,500 newborns still develop invasive GBS infections each year. In addition to neonatal disease, GBS is associated with serious infections in adult populations such as pregnant women, diabetics, and the elderly.
“We have discovered that the bacteria have evolved to use a trick we call ‘molecular mimicry,'” Victor Nizet, MD, UCSD professor of pediatrics and pharmacy is quoted as saying. “Like a wolf in sheep’s clothing, GBS can enter our body without activating the immune cells that are normally programmed to kill foreign invaders.”
The findings represent a collaborative effort between the laboratories of senior authors Nizet and Ajit Varki, MD, distinguished professor of medicine and cellular and molecular medicine. Varki is also co-director of the UCSD Glycobiology Research and Training Center, where the investigators have been exploring the interaction of bacterial pathogens with the innate immune system. Their most recent focus has been on the special role of antibodies known as Siglecs — short for sialic acid binding Ig-like lectins.
Siglecs sense a chemical structure known as sialic acid a sugar molecule that is abundant on the surface of all human cells. Many specialized Siglecs receptors recognize sialic acids as “self,” which helps keep the immune cells turned off in healthy individuals to avoid unnecessary inflammation in the absence of infection or injury.
Knowledge of how these crafty pathogens are able to fool the immune system may reveal new targets for medical therapy. According to Dr. Nizet, “Blocking engagement of the Siglecs could help boost the immune system and aid in clearing GBS infection in the critically ill newborn.”
SOURCE: Journal of Experimental Medicine, July 13, 2009