(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
