Watching the macrophage at work

Research led by the University of Plymouth in the UK has shed new light on the science behind peripheral nerve repair by highlighting the novel function of a cell called a macrophage.

Their paper, published in the journal Cell Reports, reveals how these cells, which are part of our immune system and found in most tissues, use a specific signalling pathway to control the processes of nerve repair following damage.

The nerves that connect our bodies to the spinal cord and brain consist of cable-like bundles of nerve projections (known as axons) that are insulated and protected by Schwann cells. When a nerve is injured, the two ends may separate and new tissue, known as a nerve bridge, forms between the two nerve stumps.

This new tissue consists of several cell types, including migrating Schwann cells and macrophages. The interaction between Schwann cells and macrophages is vital if the new nerve projections are to reach the skin and muscle, allowing for regeneration and a full recovery of nerve function.

The new study, conducted in mice, shows how macrophages form a collar around the outside of the nerve bridge and secrete high levels of a repulsive nerve guidance cue called Slit3. The researchers also discovered that Schwann cells inside the nerve bridge express the Slit3 interacting protein called Robo1.

Through the interaction between Slit3 and Robo1, the macrophages keep migrating Schwann cells and the regrowing nerve projections inside the bridge area.

This is a vital part of the repair process; without it, the nerve projections cannot correctly get to their targets and will never reconnect with skin and muscle, leaving patients with a permanent loss of nerve function.

Note: The link to the paper now links to the retraction and why it was withdrawn.

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