B cell receptor (BCR) mobility is reduced in Rictor knockout (KO) B cells after antigenic stimulation.

The primary B cells labeled with low concentration Alexa Fluor 647–Fab anti-immunoglobulin M (IgM) (Fc fragment antibody [Fc] specific) and high concentration Alexa Fluor 647–Fab anti-IgM (Fc specific) was placed on planar lipid bilayers containing anti-major histocompatibility complex (MHC) or anti-IgM, and single BCR molecule total internal reflection fluorescent (TIRF) images were acquired. Individual BCR molecules in TIRF images from 1 typical primary B cell indicate the instant diffusion coefficient (D0) by pseudocolored spots from 5 min to 15 min after stimulation. The display range of the pseudocolor is based on the D0 value of 10–4–0 μm²/s, a range that included most of the D0 values of the tracked BCRs. The accumulated trajectory footprints of individual BCR molecules in the entire time course (A–D). All of the D0 values were displayed as mean-square displacement (MSD) plots (E and F), single BCR molecules of the indicated numbers (G and H), and cumulative distribution probability (CDP) plots (I and J) from 3 independent experiments. Mann–Whitney U test was used to do the statistics, *p < 0.01. The numerical data (for A, B, C, D, E, F, G, H, I, and J) can be found in S1 Data.