Scientists at Duke University Medical Center have gotten to the root of the damage that the deadly Salmonella bacterium does when it kills mice: the bacteria attack lymph nodes, where immune responses, including antibodies, are raised.

The finding may also be true for humans who suffer from the infection, said senior researcher Soman Abraham, about the work published in Nature Medicine online this week.

"Salmonella quickly gets into the draining lymph node, which is unfortunate because the nodes are what the immune system uses to combat bacteria" said Soman Abraham, Ph.D., a Duke professor of pathology, immunology, and molecular genetics and microbiology. "A lymph node has a specific architecture that allows immune cell types that are capable of recognizing pathogens like bacteria to enter and interact in particular parts of the node. This way the pathogen-specific cells can identify the pathogen and create just the right antibody." Once in the lymph node, Salmonella disrupts this underlying organization.

A Salmonella infection commonly arrives through infected food and sometimes from pets, like turtles.

Abraham said that Salmonella causes "chaotic responses" in the lymph nodes and shuts the nodes down, and the damage is even visible in the microscope images his laboratory captured. "The chaos that results is how Salmonella grows without stopping in mice. We suspect there is a similar scenario in humans."

This is the first proven case of a bacterium targeting lymph nodes and altering the architecture, to effectively shut down the immune response, Abraham said.

He said would like to study the Yersinia pestis bacteria, the pathogen responsible for the Bubonic plague (which killed so many people in the 14th Century), which also infects the lymph nodes, to see if it uses the same type of attack.

The findings from Duke suggest targets for therapies to relieve the suffering of those with Salmonella. "Another tactic would be to find a way to prevent Salmonella from getting into the nodes in the first place, because once they get in, they start this destruction" Abraham said.

Dr. Abraham did the research with co-author Ashley St. John, a graduate student in immunology at Duke, now at the Duke-NUS (National University of Singapore) Graduate Medical School, Singapore. The study was funded by the National Institutes of Health.

Further reading: Microbiology publications

Labels: Salmonella, Yersinia pestis