Measuring Quality in Cultured Dairy Products

Norovirus disease is characterized by frequent vomiting and diarrhea over the course of one to two days. The most infamous norovirus, the Norwalk virus, was first identified after a 1968 outbreak at a school in Norwalk, Ohio. The Norwalk virus also caused a series of repeated outbreaks on cruise ships in 2002 and in military personnel in Afghanistan.

All previous attempts to culture human noroviruses in tissues in the laboratory have been unsuccessful, and Virgin says that as a group, noroviruses have defied characterization for decades because there has not been a way to get the virus to “grow outside of a human host.”

In 2003, Christianne Wobus, Ph.D., and Stephanie Karst, Ph.D., two postdoctoral fellows in Virgin’s lab, identified MNV-1, the first known mouse norovirus. Virgin’s group showed that mice’s ability to fight MNV-1 relied heavily on the innate immune system, the branch of the immune system that attacks invaders soon after they enter the body.

In its report, Virgin’s group reveals that MNV-1 likes to infect cells of the innate immune system. In tests in mice, the researchers found the virus thrived in macrophages, immune system cells that normally engulf and destroy pathogens, and in dendritic cells, sentry-like cells that pick up and display proteins from pathogens.

“We think there may be dendritic cells just beneath the lining of the human gut that are providing the gateway the virus needs to cause disease,” Virgin says. To grow the virus in the lab, researchers took dendritic cells and macrophages from mice with defective innate immune systems and exposed them to the virus.

“The virus grew beautifully,” Virgin says. “It’s a very facile and robust system.”