CSF1R

CSF1R (Colony Stimulating Factor 1 Receptor) is the absolute, non-redundant survival receptor for the entire microglial lineage. The sheer existence of microglia in the brain relies on continuous trophic signaling through this axis via its ligands, IL-34 and CSF-1.

When CSF1R signaling is pharmacologically blocked (e.g., via PLX3397), microglia rapidly and uniformly undergo apoptosis, allowing researchers to essentially "delete" microglia from the brain within a matter of days. Astoundingly, upon drug withdrawal, the brain repopulates the entire microglial compartment from surviving nestin-positive progenitors, entirely resetting the myeloid landscape.

Clinically, heterozygous mutations in CSF1R lead to ALSP (Adult-onset Leukoencephalopathy with Axonal Spheroids and Pigmented Glia), an aggressive neurodegenerative condition caused by primary microglial failure. In Alzheimer's and MS, CSF1R is often targeted by pharmaceutical inhibitors to "wipe out" neurotoxic, hyper-inflammatory microglial populations, with the hypothesis that forcing a repopulation might restore a younger, more homeostatic immune environment.