Fig. 8

Antigen is internalized through a myosin II-dependent mechanism. a Antigen gathering over time in control and para-Nitroblebbistatin treated cells (error bars show mean ± SEM, n = 15 DMSO, n = 9 Blebbistatin). b Scheme of the inside–out experiment and relative quantification: ratio of internalized (inside) and not internalized (outside) antigen in myosin II KO and WT B cells (error bars show mean ± SEM, n = 29 Myosin II WT, n = 21, Myosin II KO, three independent experiments, t test). c Scanning electron microscopy images showing internalized antigens and its proximity to myosin II (scale bar 0.2 µm). d Statistics of plateau of strain energy for MLSA1-treated (MLSA1) and untreated (DMSO) cells (error bar show median ± IQR, n = 41 for DMSO and n = 30 for MLSA1, three independent experiments, three mice, Mann–Whitney test): contractile energy is strongly increased in the treated cells. e Statistics of the bead displacement in the coordinated and uncoordinated compartment for treated and untreated cells: both coordinated and uncoordinated movements are significantly increased in treated cells (in red median ± IQR, Mann–Whitney test, n = 41 for DMSO and n = 30 for MLSA1, three independent experiments, three mice, total of > 4400 beads). f Average distribution of actin patches (obtained by tracking and convoluting the results with a Gaussian kernel): internal circle (2/3 cell diameter) corresponds to the central portion of the cell (scale bar represents the integrated density as number/cell/5 min). The distribution in MLSA1-treated cells is different compared with the untreated (DMSO) cells neither in number of beads (it increases but not significantly) nor g in radial profile (Mann–Withney test, Median ± IQR, N = 34 DMSO, N = 38 MLSA1, three independent experiments, three mice). h Apparent diffusion coefficient of actin patches: MLSA1-treated cells exhibit less mobile patches (number of tracks: N DMSO=301, N MLSA1=492, Mann–Whitney test). i Antigen extraction profile for MLSA1-treated and untreated cells: treated cells extract antigen faster than untreated (N = 55 DMSO, N = 53 MLSA1, three independent experiments, three mice). j Model: myosin II-driven global peripheral contractions (shear coordinated forces) allow the endocytic machinery to build up in the center, where antigen is extracted through actin protrusions associated to the generation of localized forces. Source data are provided as a Source Data file