How do microglia decide which synapses to remove? · Grey Matter

During development, weak or little-used synapses become coated with complement proteins (C1q, then C3), the same tags the immune system uses to mark bacteria for destruction.

How do microglia decide which synapses to remove?

During development, weak or little-used synapses become coated with complement proteins (C1q, then C3), the same tags the immune system uses to mark bacteria for destruction. Microglia carry the matching receptor, CR3, and engulf the tagged terminals; in the developing visual thalamus of mice, fragments of retinal terminals end up inside microglial lysosomes, and inputs that are less active are removed preferentially. Mice lacking C3 or CR3 keep too many synapses. Signals on healthy synapses that hold microglia back, such as CD47, protect the connections the circuit uses.