Siglec-1 mediates HIV-1 trans-infection in myeloid cells isolated from lymphoid tissue. A. Workflow to enrich or isolate tonsillar myeloid cells. Red numbers on the right are used throughout the figure to identify isolation procedure. B. Hierarchical clustering (by Spearman correlation) of IFNα-treated sorted Siglec-1 positive tonsillar cells and primary cells based on protein-coding gene expression. C. Venn diagram of overlapping protein-coding genes in the indicated IFNα-treated cells. D. Expression heat maps of genes with antigen-presenting cell functions shared between IFNα-treated Siglec-1 sorted tonsillar cells and at least one myeloid cell type. Data in B-D show three donors for each cell type. E. Heat map-like representation of the theoretical presence/absence profile reported for markers proposed for myeloid cell classification  in the indicated cellular subsets (dark blue: presence; light blue: absence; blue: heterogeneous expression/unknown/unclear). Observed expression in sorted Siglec-1 tonsillar cells is also depicted (dark blue: >1.5; light blue: <1; blue: ≥1 and ≤1.5 log10). Boxes indicate markers of inflammatory myeloid cells . F. Representative FACS staining of selected myeloid markers in sorted Siglec-1 positive cells (top) and BDCA1-positive cells (bottom). G. Uptake of VLPs by BDCA1-positive tonsillar cells exposed to IFNα or left untreated. Cells were pre-incubated with indicated mAbs. Mean values and SEM from three experiments include cells from eight donors, assessed with a paired t-test. H. Confocal microscopy of IFNα-treated BDCA1-positive tonsillar cells (n = 2) pulsed with HIV-1Cherry and stained for Siglec-1. Representative viral pattern (maximum fluorescence intensity of three channels and bright field). I. HIV-1 transmission from IFNα-treated sorted BDCA1-positive tonsillar cells to a reporter CD4+ cell line. Cells were pre-incubated with indicated mAbs. Values are normalized to the level of HIV-1 trans-infected by isotype-treated cells. Mean values and SEM from two experiments include mixed cells from six donors, assessed with a one sample t-test.