a, Simoa quantification of CD9, CD63, CD81, albumin and L1CAM levels in DGC fractions of CSF (left) and plasma (right). The density of fractions 1–11 were as follows in units of g ml−1: 1.012, 1.028, 1.045, 1.056, 1.065, 1.076, 1.097, 1.113, 1.138, 1.193 and 1.219. Data represent a single experiment in which a single pooled sample was used, and two technical replicates were averaged. This experiment was conducted twice with similar results. b, Schematic representation of putative L1CAM isoforms present in the human body. c, Western blotting of L1CAM immunocaptured in CSF and plasma using an antibody to the external domain of L1CAM (clone EPR23241-224). Staining was performed with one antibody to an external domain (clone UJ127) or one antibody to an internal domain (clone 2C2). This experiment was conducted twice with similar results.