The cellular requirements for the growth of BCR microclusters. (A–C) The μ-High J558L cells were treated with DMSO or the inhibitors shown (as detailed in Materials and methods), labeled with Alexa Fluor 568–Fab anti-IgM, and placed on lipid bilayers containing 10 nM NIP1-His12. TIRF images of Alexa Fluor 568 were obtained. The normalized FIs of Alexa Fluor 568–Fab anti-IgM BCR microclusters with time are shown, grouped according to the effect of the inhibitors on the growth of BCR microclusters during the early phase of the response (0–60 s; gray-shaded area) and the late phase (60–120 s; blue-shaded area). The data represent means ± SEM of the indicated numbers of BCR microclusters in three independent experiments.