Figure 8.

Combination therapy focuses the microglial response to amyloid. a, Immunostaining with Iba-1, a generic microglial marker, shows a dense gathering of microglia around amyloid cores in untreated mice. In the absence of continued amyloid deposition (dox-only and dox plus IgG), the concentration of microglia becomes less pronounced. In comparison, coadministration of Ab9 maintains the presence of microglia around amyloid foci (top row, 5×; bottom row, 63×). Nontransgenic animals show basal Iba-1 staining in the absence of pathology. b, Immunostaining with CD68, a marker of microglial lysosomes, confirmed that the cells concentrated around plaques are activated and potentially phagocytic (top row, 5×). Counterstaining with Congo red highlights the disparity between the size of plaques in each condition and the number of CD68-positive microglia surrounding them (bottom row, 63×). c, Quantitation of CD68 immunostaining indicates there is no difference in the area occupied by CD68+ microglia between dox plus Ab9-treated mice and age-matched controls. d, When considered in relation to the plaque burden carried by each treatment group, the dox plus Ab9-treated mice have significantly more CD68+ microglia per unit amyloid than any of the control groups (measured as CD68 area vs amyloid burden from Campbell–Switzer silver staining). Significant comparisons are shown for dox plus Ab9; other significant comparisons were as follows: microglial activation: pretreatment versus dox plus IgG (p < 0.001), dox only versus dox plus IgG (p < 0.01). e, The area occupied by phagocytic CD68+ microglia is relatively constant across amyloid burden and treatment condition, consistent with the idea that combination therapy focuses a fixed microglial response around less remaining amyloid. There is no correlation between percentage CD68 area and amyloid load measured by Campbell–Switzer silver stain [slope of the linear regression is not significantly different from 0 (p = 0.94, R² = 0.0001); dashed lines indicate the 95% confidence interval].