Pediatric researchers at the San Diego School of Medicine in California have discovered a link between a particular strain of the Streptococcus bacteria and premature births. The Strep family of bacteria may be more widely known as the cause of Strep throat but the strain in question — group B Streptococcus (GBS) — can cause life-threatening illness in babies born prematurely.

The study, led by Dr. Victor Nizet, a pediatrics and pharmacy professor at the California medical school, led the team that discovered a genetic interaction in the immune system between two proteins that determine how the body reacts to GBS. Roughly 15% to 20% of all healthy women of childbearing age have GBS colonization of their vagina or lower gastrointestinal tract.

The presence of GBS alone poses no threat to the woman but exposure to the bacteria during the birthing process can cause serious illness to the baby, especially if it is a premature baby. Meningitis and sepsis are two serious concerns.

The Nizet research team focused on two proteins that bind to the GBS bacteria:

  • Siglec-14, which activates an immune-system attack on GBS.
  • Siglec-5, which stops an immune-system attack on GBS.

The Nizet team describes the interaction between the protein and the bacteria as “GBS-Siglec crosstalk” which regulates Strep-induced inflammation of placental membranes. Excess inflammation of the placenta is a triggering factor for premature labor.

The researchers discovered that when Siglec-14 is missing, as it is naturally in some people, the risk of premature delivery is greater than in those with both Siglec proteins. The research suggests an absence of the Siglec-14 (the “attack” protein) increases placental inflammation to the point of threatening the health of the pregnancy.

Discovery of how the Siglec proteins work as a system of checks-and-balances for the immune system could lead to treatment options that rescue pregnancies in jeopardy of premature birth. Other applications are possible, too. The research team suggests a greater understanding of how the two proteins regulate the body’s immune response to the Strep bacteria could lead to improved treatment options for other medical conditions that include antibiotic-resistant bacterial infections, blood clots, certain chronic diseases, and HIV.

Dr. Ajit Varki, a co-author of the study, says the study “offers intriguing insights into why certain bacterial pathogens may produce uniquely human diseases.” Although humans share 99% of their genetic material with chimpanzees, chimps don’t harbor the GBS bacteria, nor do any other animals. It’s a strictly human phenomenon.

Source: Nizet, Victor, et al. “Siglec-5 and Siglec-14 are polymorphic paired receptors that modulate neutrophil and amnion signaling responses to group B Streptococcus.” JEM. The Rockefeller University Press. May 5, 2014. Web. Jun 3, 2014.