Enzyme linked immunosorbent assay

Briefly, an optional baseline, fasting, lumbar puncture procedure aided CSF collection using a polypropylene syringe and a Sprotte 25-gauge spinal needle from an intervertebral lumbar space. CSF supernatant was immediately extracted and stored at -80 °C. Commercially available kits were used for the measurement of CSF total tau, p-tau181, Aβ_x-40, Aβ_x-42, Aβ_1-42, neurofilament light (NfL) and albumin concentrations, performed in batch, as previously described. Albumin was measured in both CSF and plasma by immunonephelometry [15 (link)]. A Meso Scale Discovery (MSD) assay (Rockville, MD) was used to measure sTREM2 levels in CSF, described by Jensen et al., 2019 [27 (link)]. Commercially available enzyme-linked immunosorbent assays (Fujirebio, Ghent, Belgium) were used to determine the levels of Aβ₄₂ (INNOTEST β-AMYLOID(1–42)) and the subsequent Aβ₄₂/Aβ₄₀ ratio [24 (link)]. Biotinylated polyclonal goat anti-human TREM2 capture antibodies (R&D Systems BAF1828) were incubated with recombinant human TREM2 protein (Sino Biological Inc. 11084-H08H) and a SULFO-TAG–labeled anti-mouse secondary antibody was used for detection. More detailed kit information is provided in Supplemental Table 1.

A subset of participants completed an optional morning fasting lumbar puncture at enrollment (n = 55, Supplementary Figure 1). CSF was collected with polypropylene syringes using a Sprotte 25-gauge spinal catheter. Samples were immediately centrifuged, aliquoted into 0.5 mL polypropylene tubes, and stored at −80°C. Samples were analyzed in single batch, and commercially available enzyme-linked immunosorbent assays (Fujirebio, Ghent, Belgium) were used to measure CSF concentrations of Aβ₄₂ [INNOTEST^® β-AMYLOID_(1–42)], phosphorylated tau [p-tau, INNOTEST^® PHOSPHO-TAU_(181P)], total tau (t-tau, INNOTEST^® hTAU), neurogranin (Kvartsberg et al., 2015 (link)), and NFL (Uman Diagnostics). Board certified laboratory technicians processed samples blinded to clinical information (Palmqvist et al., 2014 (link)). Intra-assay coefficients of variation were < 10% (Kvartsberg et al., 2015 (link)).

A subset of participants completed a fasting lumbar puncture (n = 104). CSF was collected with polypropylene syringes using a Sprotte 25-gauge spinal needle in an intervertebral lumbar space. Samples were immediately mixed and centrifuged, and supernatants were aliquoted in 0.5 mL polypropylene tubes and stored at −80 °C. Samples were analyzed in batch using commercially available enzyme-linked immunosorbent assays (Fujirebio, Ghent, Belgium) to determine the levels of Aβ₄₂ (INNOTEST β-AMYLOID_(1–42)), p-tau (INNOTEST PHOSPHO-TAU_(181P)), and t-tau (INNOTEST hTAU) (Osborn et al., 2018 (link)). Board-certified laboratory technicians processed data blinded to clinical information, as previously described (Palmqvist et al., 2014 (link)).