C5 and Alzheimer disease: When comparing AD and MCI groups, neural cell-derived sEV Aβ42, Aβ42/40, t-Tau, p-Tau, p-Tau181, NfL, C4b, Factor D, fragment Bb, C5b-C9 TCC, and miR-29c-3p showed significant increases, while GAP43, neurogranin, SNAP25, and synaptotagmin 1 exhibited significant decreases.