MAPT and Alzheimer disease: Because FcγRIIb itself did not affect Aβ levels in these mice (Figure 1—figure supplement 3A) and the hippocampus of 3xTg-AD mice at nine months of age was plaque-free (Hirata-Fukae et al., 2008), we next examined the role of FcγRIIb in tau pathology in the mouse brains.