Scientists at the University of Washington have discovered that a common type of cell in the vertebrate immune system plays a unique role in communication between other cells. It turns out that these cells, called macrophages, can transmit messages between non-immune cells.

Their paper, published online Feb. 16 in the journal Science, describes how pigment cells in a species of fish have co-opted macrophages to deliver messages important for pigment patterning in skin. This is the first reported instance of macrophages relaying messages over a long distance between non-immune cells. But since the macrophages are common to all vertebrates, the researchers believe their discovery is no quirk of aquatic life. Macrophages may be common interlocutors for long-distance messages among cells.

“If pigment cells have figured out how to use macrophages for signaling, it stands to reason that others have as well,” said senior author and UW biology professor David Parichy. “This could occur in a variety of cells and animals.”

Parichy and lead author Dae Seok Eom, a UW postdoctoral researcher, discovered this new role for macrophages while studying zebrafish. They had wanted to understand how the zebrafish gets its telltale stripes of silver-yellow and black. Each color — black, yellow and silver — arises from a different type of pigment cell. When zebrafish are juveniles, these pigment cells migrate to the right spot to create the stripes.

“As they migrate, communication among these three populations of pigment cells is critical to forming the stripes we see in adult zebrafish,” said Parichy.

Eom and Parichy used laboratory genetic tools to make zebrafish pigment cells glow fluorescent colors — making these cells easier to track using a microscope. In the process, they discovered that xanthoblasts — the precursors to yellow pigment cells — produced unique, elaborate projections during the peak time for pigment pattern formation.

Read the full article on UW Today.