Figure 2. Microglial caspase-8 deficiency ameliorates proinflammatory microglia activation in the substantia nigra in response to intranigral LPS injection. Panel (a) shows an illustration of Iba1 and CD16/32-labeled microglia in the ventral mesencephalon in response to either saline or intranigral LPS in Casp8fl/fl mice and CreLysMCasp8fl/fl mice. The effect of LPS and caspase-8 deficiency on the number of total microglia (Iba1) or proinflammatory microglia (CD16/32) in the substantia nigra is shown in panels (b) and (c). Results are the mean ± SD of a minimum of four independent experiments and are expressed as number of cells per mm2. Statistical significance was calculated by analysis of variance followed by the least significant difference post hoc test for multiple range comparisons (p <0.05). Panel (d) shows an illustration of dual immunofluorescence of Iba1 and CD16/32-labeled microglia in the ventral mesencephalon in response to saline or intranigral LPS in Casp8fl/fl mice and CreLysMCasp8fl/fl mice. Merge photographs shown in (d) are higher magnification photographs of dot boxes depicted in the left column. Note the completely different morphological features of microglia in response to saline or LPS (d). No apparent differences in terms of Iba1 were detected between Casp8fl/fl mice and CreLysMCasp8fl/fl mice (a, b, d). Also note the specific labeling of CD16/32, a proinflammatory marker of microglia activation, which is located in the membrane of microglia (d). Also note how the expression of CD16/32 is clearly down-regulated in response to caspase-8 deficiency (a, c, d). Scale bar: a, 100 μm; d: Iba1 and CD16/32 staining: 50 μm; merge: 20 μm.