Fig. 6. Cell type–specific induction of immunity induces invasion of macrophages.

(A) Pan-glial activation of immunity response triggers invasion of many macrophages into the CNS (n = 10 for repo>>PGRP-LE; n = 4 for all other genotypes). When pan-glial PGRP-LE expression was blocked in various glial subtypes, the number of invading macrophages is reduced. The color coding of the different glial subtypes is indicated below. For further information about the different Gal4 drivers, see Materials and Methods, Table 3. (B) Concomitant silencing in cortex and ensheathing glia using nrv2-Gal80 causes a similar reduction in the number of invading macrophages as concomitant silencing in astrocyte-like glial cells using alrm-Gal80. (C) Upon PGRP-LE expression in all glial cells but the BBB, only very few macrophages entered the brain (arrowhead) (repo-Gal4, moody-Gal80, and Tret1-1-Gal80 UAS-PGRP-LE). (D) Average number of invading macrophages in different expression regimes (n = 10 for repo>>Pvf2; otherwise, n = 4). Color coding is as in (A). In all expression regimes, macrophages enter the brain, except for moodyB4-Gal4–driven Pvf2 expression. (E) Notably, even expression of Pvf2 in only few neurons (GMR14F11-Gal4 is active in the mushroom bodies only, shown by concomitant expression of UAS-CD8-GFP), is able to recruit macrophages into the brain lobes [open arrowhead indicates macrophage associated with mushroom body, and filled arrowhead indicates macrophage located in some distance (E and E′)]. Scale bars, 100 μm.