A soluble proteoform of CCL21 (CCL21-ΔC) with chemotactic activity is present in murine skin and increased in CHS-inflamed skin. (A) Representative western blot of CCL21 performed on steady-state (CTR) and CHS-inflamed (CHS) murine ear skin protein extracts. Recombinant CCL21 was loaded as a CTR. (B) Western blot analysis of recombinant human full-length CCL21 and CCL21-ΔC protein. One out of two experiments is shown. (C) Quantification of the full-length CCL21 (gray) and CCL21-ΔC (white) relative band percentages. Pooled data from n = 4 independent biological replicates. (D) ELISA-based quantification of total CCL21 in tissue protein extracts, performed with antibody clone AF457, which detects full-length CCL21 and CCL21-ΔC. Pooled data from n = 5 mice/condition. Statistics: unpaired Student’s t test. (E–J) Skin elution assay and analyses were performed on the supernatants. (E) Schematic depiction of the assay and representative western blot analysis. (F) Image-based quantification of the CCL21-ΔC band intensity from western blots as in E. A.U., arbitrary units, as produced by the western blot imager (G) ELISA-based quantification of total CCL21, performed with antibody clone AF457. Pooled data from n = 6–7 mice/condition, with one CHS-inflamed and a contralateral CTR ear, are shown in E and F. Data from the same mouse are connected by a line. The mean is shown in red, paired Student’s t test. (H–J) Transwell chemotaxis assays were performed on elution assay supernatants (see E) with 1:1 mixtures of LPS-matured labelled WT and CCR7−/− DCs in presence/absence of a CCL21-blocking antibody. Flow cytometry–based quantification of the total numbers of transmigrated (H) WT DCs and (I) CCR7−/− DCs, as well as of (J) the ratio of transmigrated WT to CCR7−/− DCs. Data points from 3–7 experiments per condition are shown. Mixed effects statistical analysis. (K) Ratio of WT: CCR7−/− DCs measured in seven paired experiments performed for CTR and CHS-inflamed condition. Statistical analysis: paired Student's t test. (L and M) Western blot analysis of protein extracts of (L) steady-state human skin (CTR) and (M) donor-matched steady-state (CTR) and inflamed (INF) human skin from a psoriasis patient. Data from one out of two experiments in L and one experiment in M are shown. Recombinant human full-length CCL21 was loaded as a CTR. Source data are available for this figure: SourceData F3.