Figure 5. Bacterial infection in neonatal male rats alters long-term microglial morphology, surface antigen expression, and function.

(A) Male rats treated on P4 with PBS or live E. coli were injected systemically as adults with saline (SAL) or 25 µg/kg lipopolysaccharide (LPS), and microglia were rapidly isolated from whole HP 24 h later following cold saline perfusion to eliminate infiltrating cells as described in detail previously (Frank et al.; Henry et al., 2009). Isolated microglia were stained for APC-conjugated CD11b. Cell size (forward light scatter) and CD11b+ expression were assessed using a FACSCanto™ II flow cytometer (Becton, Dickinson and Co.) and FlowJo™ software (Treestar, Inc.). The gating strategy and representative contour plot are shown. (B) There is a greater proportion of large, CD11b^bright microglia in adult rats infected neonatally with E. coli. Mean fluorescence of CD11b+ staining in gated cells was also greater on a per cell basis in rats infected neonatally with E. coli. *Overall effect of E. coli for each, p<0.01. (C) Sensitized/primed microglia in neonatally-infected rats produce more IL-1β in response to LPS in adulthood compared to controls (Bilbo et al., 2005a; 2007; Bilbo et al., submitted data).