Changes in neural circuitry after brain injury can help the nervous system to heal. In a recent study, researchers have demonstrated that molecules known for their functions in the immune system can constrain brain plasticity after stroke (Neuron 73, 1100–1107).

Major histocompatibility class I (MHCI) molecules present antigens on the surface of cells to stimulate the immune system, and paired immunoglobulin-like receptor B (PirB) is a receptor for MHCI molecules. MHCI and PirB are both expressed on neurons and are known to have a role in neural plasticity during development, so Jaimie D. Adelson et al. asked whether they could also be targeted to induce functional recovery after stroke.

The researchers found that stroke increased the expression of two MHCI subtypes as well as PirB in the mouse brain; mice lacking these proteins had better functional outcomes and less brain damage after stroke. This improvement seemed to be linked to an increase in axon projections from the uninjured cortex of these mice to the affected side of the body, although exactly how the MHCI molecules and PirB receptor affect this process remains to be determined.