Figure 4.

Microglia are a sufficient source of MFG-E8. A, Reconstitution of microglia-depleted Mfge8 knock-out cultures with wild-type microglia is sufficient to restore LPS-induced neuronal loss (n = 3). B, MFG-E8 is largely expressed by astrocytes in vitro, although microglia are highly opsonized with MFG-E8 protein after treatment with LPS. Mfge8 knock-out cultures express β-galactosidase under control of the endogenous Mfge8 promoter. β-Galactosidase activity specific to Mfge8 knock-out cultures was largely associated with astrocytes (GFAP-positive, left). Immunocytochemistry for external MFG-E8 protein shows that wild-type microglia (IB4-positive) retain high amounts of MFG-E8 protein on their surface (right). C, Immunocytochemistry for external MFG-E8 protein shows that purified Mfge8 knock-out microglia (IB4-positive) can be opsonized with MFG-E8 protein (in red, top) present in conditioned medium from wild-type astroglial cultures. Scale bar, 10 μm.