Human anogenital mucosae contain various tissue types, which represent unique opportunities and barriers for transmission of viruses, and each of these tissues should be considered separately in terms of how transmission occurs. Dendritic cells (DCs) and macrophages present in these tissues are two of the first cell types to encounter viruses during sexual intercourse. Furthermore, these cells play a direct role in the transmission of some viruses such as HIV where they transfer the virus to T cells in which explosive replication occurs.

Different anogenital tissues are likely to contain unique combinations of DC and macrophage subsets however very little human data is available concerning these differences. Therefore, we have gained access to all the anogenital tissues that HIV encounters during transmission (labia, vagina, cervix, glans penis, foreskin, anus and rectum). Using flow cytometry we have thoroughly characterised the immune populations found in these tissues. Critically, we have identified key differences in specific immune cell subsets present in different anogenital sites and in the viral binding receptors they express. Furthermore we identified which cell subsets are most efficient at transferring HIV to T cells.

Understanding the differences in composition of immune cells that interact with viruses in anogenital tissues is critical in the development of strategies to block transmission and in mucosal vaccine development. This is particularly the case for anorectal tissue as there is little knowledge available on its immune cell composition. This represents a key gap in our understanding as transmission across this tissue is hundreds of times more efficient in the case of HIV.