HTLV biofilm-like structures trigger a robust activation of pDC-IFN-I response.

A. Representative confocal imaging of pDC/HTLV-1 infected cell contact with 3 consecutive Z-stack sections (left to right, all immunodetections were performed without permeabilization). Upper panels, confocal analysis of HTLV-1 Env gp46 (green) that form cluster at the contact between HTLV-1 infected cells and pDCs (stained with DiI, a lipophilic dye, red). Carbohydrate-rich structures are stained by the WGA lectin (Triticum vulgaris, purple), and nuclei are stained with Hoescht (blue). Middle and lower panels, single detections of WGA lectin and HTLV-1 Env gp46, respectively. B. Quantification of the presence or not of Env gp46 and WGA co-clusters at the cell-cell contact (analysis of 16 cell-cell contacts in 3 independent experiments). C-D. Parallel quantification of IFN-I activity in SNs of pDCs co-cultured with HTLV-1-infected cells (C91-PL) versus biofilm-like structures isolated from HTLV-1-infected cells (C91-PL) and infectivity transmission levels, determined as in Figs 1G and 2D (mean ± SD; 3 independent experiments performed with similar viral capsid levels in the isolated HTLV-1 biofilm-like structure as determined by p19gag levels, i.e. 2.9 ng). Asterisks indicate statistically significant differences calculated using ANOVA followed by Sidak’s multiple comparison test: **** pE. Surface Env gp46 detection on HTLV-1 infected cells (C91-PL) treated or not with metalloproteinase 9 (MMP-9; 20 nM). F-G. Parallel quantifications of IFN-I activity in SNs of pDCs co-cultured with HTLV-1-infected cells (C91-PL) treated or not with MMP-9 as in C, and infectivity transmission levels to Jurkat reporter cells co-cultured with HTLV-1-infected cells (C91-PL) treated or not with MMP-9 determined as in Fig 2D. The results are representative of 3 independent experiments.