Fig 1.
Activation of microglia by small amyloid plaques.
On brain slices of 12-month- old APP-PS1(dE9) mice microglial cells were immunohistochemically labelled for Iba1 (green) and amyloid plaques were stained with Methoxy-X04 (red). Small amyloid plaques were imaged and classified according to the microglial status. A Image projections of an amyloid plaque lacking any microglial contact (level 0) at three magnifications. Below, the single x-y-planes clarifying that no microglial process touches the plaque. B Exemplary images of the stages of plaque-associated microglial (MG) activation (level 1 to level 4). The upper lower magnification illustrates the microglial environment around the plaque, the higher magnification below highlights the individual plaque. Notice that, although each plaque has a similar size, microglial reaction is diverse. C Small plaques were classified according to their microglial activation level and plotted against the plaque volume. D The number of microglial cells associated to the individual plaques was plotted against the plaque volume. (The brains of five animals were analysed with a total of 188 small plaques. Red bars show mean with standard deviation.)
Fig 2.
In vivo monitoring of amyloid plaque induced microglial activation.
In the cortex of PS1(dE9)xCX3CR1+/- mice, individual new appearing plaques (red, Methoxy-X04 stained) and the subsequent microglia activation (green) were followed using two-photon microscopy. A Time series of image projections of a newly formed plaque (starting with day 1) and the corresponding microglial reaction. The upper row indicates the microglial environment, the lower row shows the plaque in higher magnification. Notice, at day 1 a microglial process is already contacting the plaque (level 1). At day 9 this plaque was classified as level 3 and level 4 was reached at day 29. Interestingly, at day 88 the plaque is mainly liberated from enclosing microglia, which at day 92 is reverted to level 4 again. B Time dependent development of microglial activation level for each plaque (colour coded) beginning with the time point of appearance. The box plots below indicate the distribution of initial time points when microglia activation was reached (level 3 and 4). C Size dependent development of microglial activation for individual plaques (colour coded). The box plots below indicate the distribution of initial volume when microglia activation was reached (level 3 and 4). D No correlation between plaque lifetime and plaque volume when microglial activation level 3 or 4 are reached.