The mucosal barriers and HIV/SIV target cell composition. (A) Immunofluorescent micrographs (200×) of endocervix, ectocervix/vagina, and rectum stained for CD3⁺ T cells (green) and CD11c⁺ DCs (red) from a representative SIV-negative RM. The 2 different columns show the diversity and abundance of potential target cells in the same animal along the different mucosal barriers. The thickness of the respective epithelial barriers (in micrometers) is indicated in each image to highlight the heterogeneity that can exist in the thickness of the barrier that separates the host from its environment. (B) Immunofluorescent micrograph (200×) of vagina stained for CD3⁺ T cells (green) and CD11c⁺ DCs (red) from a SIV-negative RM with subclinical mucosal inflammation. The arrows point to regions of epithelial thinning where potential target cells are directly juxtaposed to the lumen. Note the densely packed T-cell infiltrate with numerous DCs beneath what remains of the epithelial barrier.