Figure 2: CD4 T cells and APC cluster around hair follicles at steady state.

(a) Naive flank skin, detecting peri-follicular CD4 T cells (orange). Scale bar, 100 μm. (b) Location of peri-follicular clusters; n=10, determined by (c) stains that recognize EpCAM (left image) or the arrector pilli muscle (identified by anti-smooth muscle actin) (right image). Scale bar, 30 and 100 μm, respectively. (d) Peri-follicular cluster, detecting CD4 (white), CD11c (green) and MHC class II (red) positive cells. Scale bar, 50 μm. (e) Naive skin of MHC II^−/− mice injected intradermally with in vitro activated wild-type GFP⁺ CD4 T cells (green). Scale bar, 100 μm. (f) Location of CD4 T cells within the dermis of naive skin; n=11. (g,h) Microscopy of healthy human skin staining for (g) CD3 (white) and CD11c (red) and (h) CD3 (white) and CD4 (green). Scale bar: 100 μm (g); and 50 μm (h). Graph in h shows the frequency of peri-follicular CD3⁺ cells that are CD4⁺, n=17. Each symbol in f represents the indicated CD4 T-cell population in a single mouse or skin sample from an individual person (graph of h). NS, not significant (two-tailed paired t-test). Data are representative of four (a) or two (c–e) experiments with two to five mice, or pooled from two (b) or three (f) experiments. Graph in (h) is pooled from 16 individual experiments. Line in f,h indicates mean.