Background
Cell-to-cell HIV-1 transmission is a potent mechanism of HIV-1 pathogenesis. B and CD4+ T cells frequently interact in secondary lymphoid organs (SLO), thus potentially promoting B cell mediated HIV-1 trans infection. In SLO, B cells are stimulated through both stromal (BAFF) and CD4+ T cell (IL-4, IFN-g, CD40L) signals, however the impact of these signals on the efficiency of HIV-1 binding and trans infection remains unknown.
Methods
Human B and CD4+ T cells were isolated from blood of people without HIV. B cells were left unstimulated or stimulated with CD40L/IL-4, CD40L/IFN-g, BAFF/IL-4, or BAFF/IFN-g. For trans infection, B cells were incubated with HIV-1BaL (MOI 10-3) prior to culture with CD4+ T cells. HIV-1 infection was measured by HIV-1 p24 ELISA on co-culture supernatants. For HIV-1 binding, B cells were incubated with HIV-1 Gag-iGFP-JRFL (MOI 10-1) and analyzed by flow cytometry. ScRNAseq was performed via the BD Rhapsody and Illumina platforms and data were analyzed using the Seurat package in R.
Results
CD40L/IL-4 stimulated B cells efficiently bound HIV-1 (p<0.0001) and mediated HIV-1 trans infection of CD4+ T cells (p<0.0001) as compared to the other stimulation conditions. Exposure to CD40L was the main driver of HIV-1 binding by B cells, although IL-4 also contributed to some extent (p=0.01). Single cell transcriptomics of B cells stimulated for 10h provided unique insights into the gene expression profiles associated with these conditions. CD40L/IL-4 stimulated B cells exhibited significantly higher expression of activation markers CD80/CD86 as well as C-type lectin CD205 (p<0.01), which flow cytometry confirmed (p<0.0001). Antibody-mediated blocking of CD205 on CD40L/IL-4 stimulated B cells reduced HIV-1 binding. Biological processes analysis further highlighted that CD40L/IL-4 upregulates genes involved in actin pathways in B cells, including actin filament organization (p<0.01). When actin polymerization was blocked in CD40L/IL-4 stimulated B cells, HIV-1 binding was also reduced.
Conclusions
B:T cell interactions in SLO likely play a key role in HIV-1 pathogenesis by facilitating HIV-1 trans infection. This study identifies the signals (CD40L/IL-4) and gene/receptor expression (CD205/actin) that enable B cells to bind HIV-1 and transfer virus to CD4+ T cells. This information could lead to the development of treatments to reduce persistent HIV-1 infection and maintenance of the viral reservoir.
Table or Figure
