HIV transmitting mononuclear phagocytes; integrating the old and new

Abstract

In tissue, mononuclear phagocytes (MNP) are comprised of Langerhans cells, dendritic cells, macrophages and monocyte-derived cells. They are the first immune cells to encounter HIV during transmission and transmit the virus to CD4 T cells as a consequence of their antigen presenting cell function. To understand the role these cells play in transmission, their phenotypic and functional characterisation is important. With advancements in high parameter single cell technologies, new MNPs subsets are continuously being discovered and their definition and classification is in a state of flux. This has important implications for our knowledge of HIV transmission, which requires a deeper understanding to design effective vaccines and better blocking strategies. Here we review the historical research of the role MNPs play in HIV transmission up to the present day and revaluate these studies in the context of our most recent understandings of the MNP system.

Fig. 1. Current mononuclear phagocyte subsets represented in existing HIV literature.

A selection of existing literature describing HIV interactions with transmission site mononuclear phagocytes were selected for re-examination. Based on the phenotypic data that was presented (left column lists the publications that were assessed, the tissue studied, and the defining phenotypic characteristics presented by the authors), key HIV transmitting mononuclear phagocytes from each study were categorised into the current mononuclear subsets (the columns on the right). This does not consider the proportional contribution that each subset represents, only whether each described mononuclear phagocyte matches the phenotypic profile of the current subset.