Siglec-1 mediates HIV-1 uptake into a storage compartment and enhances HIV-1 trans-infection specially in IFNα-treated monocytes and DCs. A. Uptake of HIV-1NL4–3 by different myeloid cells exposed to IFNα. Cells were cultured with HIV-1 to measure p24Gag by ELISA. Mean values and SEM from four experiments include cells from 12 donors. B. Fold change in HIV-1NL4–3 uptake of cells treated with bafilomycin A1 compared to untreated cells. Mean values and SEM include cells from three donors. C. Relative uptake of HIV-1NL4–3 by IFNα-treated myeloid cells pre-incubated with the indicated mAbs. Values are normalized to the level of HIV-1 uptake by mock-treated cells (set at 100%). Mean values and SEM from two experiments include cells from six donors. D. Confocal microscopy analysis of different IFNα-treated myeloid cells pulsed with HIV-1Cherry and stained for Siglec-1 (Alexa 488), HLA-DR (Alexa 647) and DAPI. (Top) Representative viral pattern for each kind of myeloid cell analyzed, showing maximum fluorescence intensity of four channels. (Bottom) Percentage of myeloid cells with distinct viral patterns: random distribution, polarized accumulation, and sac-like compartment formation, as illustrated in the left drawing. Mean values of 50 cells from two different donors are shown. E. HIV-1 transmission from IFNα-treated myeloid cells to a luciferase reporter CD4+ cell line. HIV-1 infection was determined by induced luciferase activity in relative light units (RLUs). Mean values and SEM from four experiments include cells from 12 donors. F. Relative HIV-1 transmission from IFNα-treated myeloid cells pre-incubated with the indicated mAbs. Values are normalized to the level of HIV-1 trans-infected by mock-treated cells. Mean values and SEM from two experiments include cells from six donors. Statistical differences were assessed with a paired t test in A and E, and with a one sample t-test in B, C and F.