APP and Alzheimer disease: At least two factors, in addition to the lack of NFTs, mitigate against complement activation in the APP mouse being equivalent to that in AD: (a) the mouse complement system is functionally deficient, as mouse C4 lacks C5 convertase activity [93] and many mouse strains have low complement levels relative to other mammals [94], and (b) mouse C1q binds less efficiently to human Aβ than does human C1q, resulting in less activation of mouse complement than of human complement in the presence of human Aβ [95].