Abstract
Ex vivo foreskin models have demonstrated that inner foreskin is more susceptible to HIV-1 infection than outer foreskin. In the present study we characterized the compartition of HIV-1 target cells and quantified these cells in the epidermis and dermis of inner and outer foreskins using immunohistochemistry and flow cytometry. Our data showed that the epidermis of the inner foreskin was more enriched with CD4+ T cells and Langerhans cells (LCs), with the co-expression of CCR5 and α4β7 receptors, than the outer foreskin. Interestingly, the vast majority of CD4+ T cells and LCs expressed CCR5, but not CXCR4, indicating that the inner foreskin might capture and transmit R5-tropic HIV strains more efficiently. In addition, lymphoid aggregates, composed of T cells, macrophages and dendritic cells (DCs) in the dermis, were closer to the epithelial surface in the inner foreskin than in the outer foreskin. As dendritic cells are able to capture and pass HIV particles to susceptible target cells, HIV may be able to more efficiently infect the inner foreskin by hijacking the augmented immune communication pathways in this tissue. After the inoculation of HIV-1 particles in a foreskin explant culture model, the level of p24 antigen in the supernatant from the inner foreskin was slightly higher than that from the outer foreskin, although this difference was not significant. The present study is the first to employ both CCR5 and α4β7 to identify HIV target cells in the foreskin. Our data demonstrated that the inner foreskin was more enriched with HIV target immune cells than the outer foreskin, and this tissue was structured for efficient communication among immune cells that may promote HIV transmission and replication. In addition, our data suggests the R5-tropism of HIV sexual transmission is likely shaped through the inherent receptor composition on HIV target cells in the mucosa.
Highlights
Sexual transmission accounted for 84.9% of newly infected HIV cases in 2012 [1], and the large majority of people living with HIV in China were male [2]
The surface markers employed for immunohistochemical staining to identifiy potential HIV-1 target cells included CD3, CD207, CD209, CD68, and the HIV-1 receptor CD4
It has been hypothesized that keratin provides an impermeable barrier to HIV-1 and the inner foreskin is more thinly keratinized; the removal of the inner foreskin through circumcision is protective against HIV-1
Summary
Sexual transmission accounted for 84.9% of newly infected HIV cases in 2012 [1], and the large majority of people living with HIV in China were male (only 28.6% were women) [2]. Other penile sites, such as the urethra, might play a role in HIV acquisition[11], the importance of the foreskin is shown by the observation that increased foreskin surface area is associated with an increased risk of HIV-1 infection[12]. The foreskin is retracted and this inner aspect is exposed to potentially infectious secretions. Both this inner aspect of the foreskin and a contiguous portion exposed on both the erect and non-erect penis, termed the ‘‘outer foreskin’’, are removed during circumcision. The inner surface of the foreskin, which is exposed to vaginal secretions during intercourse, contains both T cells and Langerhans cells (LCs) that express HIV receptors as potential targets for viral entry [15,16,17]
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