Immune cells found in breast ducts

Australian researchers have discovered a new type of immune cell they say helps keep breast tissue healthy by regulating a process within mammary ducts, where most breast cancers arise.

Using advanced 3D imaging techniques, they observed how the cells monitor for threats in the ducts and “eat” dying milk-producing cells needing to be cleared away once lactation stops.

The preclinical research, led by the Walter and Eliza Hall Institute, is described in a paper in the journal Nature Cell Biology.

Co-author Caleb Dawson says the team discovered the new population of specialised cells, which they named ductal macrophages, between two layers of the mammary duct wall.

“We watched incredulously as the star-shaped ductal macrophages probed with their arms and ate away at dying cells,” he says. 

“The clearing action performed by ductal macrophages helps redundant milk-producing structures to collapse, allowing them to successfully return to a resting state.”

When the researchers later removed ductal macrophages from the mammary ducts, they discovered that no other immune cells were able to swiftly carry out the process.

Dawson says the team plans to explore the function of ductal macrophages at different stages of mammary gland development, such as the transitions into adulthood and pregnancy.

“We also want to investigate the role that these duct-specific immune cells play in helping cancer to grow and spread,” he says.

“Ductal macrophages are spread throughout the mammary ducts. As cancer grows, these macrophages also increase in number. 

“We suspect that there’s the potential for ductal macrophages to inadvertently dampen the body’s immune response, which would have dangerous implications for the growth and spread of cancer in these already prone sites.”

The ultimate goal is to understand the cells well enough to manipulate them.