Fig. 3. In situ division of CD8⁺ T cells in the FRT.

a,b, Accumulation of P14 CD8⁺ T cells after local T_RM cell reactivation in FRT. a, Representative maximal projections of 3D z-stack images of GFP⁺CD8⁺ P14 T cells (cyan) after trans-cervical challenge with gp33. Scale bars, 30 μm. b, The abundance of P14 CD8⁺ T cells enumerated by QIM in 7-μm sections of FRT. c, Top, representative time-lapse images (time stamps in minutes and seconds are shown above the images) of GFP⁺CD8⁺ P14 T cells (cyan) undergoing division beginning ~36 h after gp33 challenge. Scale bars, 40 μm. Bottom, magnified views (4× magnification compared with the images above) of dividing cells, indicated by white arrowheads (or two yellow arrowheads for cells after cytokinesis). Magnified cells are outlined by white rectangles in the images above. d, P14 immune chimeras were challenged with peptides (gp33 or SIINFEKL) or mock-challenged (with PBS), and tissues were harvested 48 h after challenge. Animals received 2 mg of BrdU i.p. before cell collection. e, OT-I immune chimeras were challenged with viruses (VV-OVA and VV-gp33) or mock-challenged, and tissues were harvested 48 h after recall. In d and e, numbers in corners indicate the percentage of cells in each quadrant. f,g, The frequency of Ki67⁺ cells in FRT of the mice described in d (see f) and e (see g). SIIN, SIINFEKL. h, Instantaneous track speed versus time, beginning 15min before cytokinesis, for four representative dividing and four nondividing P14 CD8⁺ T cells. i, The mean track speed of dividing and nondividing cells 36h after recall. *P< 0.05, ***P< 0.001, Mann-Whitney U-test. Data in b,f-i are shown as the mean ± s.e.m. Data are representative of two separate experiments with 3 (a,b) or 4 (f,g) mice per group per experiment or are pooled from 6 individual movies and 3 animals (i).