TREM2 and Alzheimer disease: In order to evaluate the effect of AD-linked mutations on TREM2 binding to TREM2-L, we constructed a novel TREM2 protein cell-binding reagent containing a site-specific BirA-biotinylation sequence on the C-terminus of TREM2, which could then be complexed with PE-labeled streptavidin to create a tetrameric cell-staining reagent (Figure 4a).