Abundant Expression of HIV Target Cells and C-Type Lectin Receptors in the Foreskin Tissue of Young Kenyan Men

A biological explanation for the reduction in HIV-1 (HIV) acquisition after male circumcision may be that removal of the foreskin reduces the number of target cells for HIV. The expression of potential HIV target cells and C-type lectin receptors in foreskin tissue of men at risk of HIV infection were thus analyzed. Thirty-three foreskin tissue samples, stratified by Herpes simplex virus type 2 status, were obtained from a randomized, controlled trial conducted in Kenya. The samples were analyzed by confocal in situ imaging microscopy and mRNA quantification by quantitative RT-qPCR. The presence and location of T cells (CD3⁺CD4⁺), Langerhans cells (CD1a⁺Langerin/CD207⁺), macrophages (CD68⁺ or CD14⁺), and submucosal dendritic cells (CD123⁺BDCA-2⁺ or CD11c⁺DC-SIGN⁺) were defined. C-type lectin receptor expressing cells were detected in both the epithelium and submucosa, and distinct lymphoid aggregates densely populated with CD3⁺CD4⁺ T cells were identified in the submucosa. Although the presence of lymphoid aggregates and mRNA expression of selected markers varied between study subjects, Herpes simplex virus type 2 serostatus was not the major determinant for the detected differences. The detection of abundant and superficially present potential HIV target cells and submucosal lymphoid aggregates in foreskin mucosa from a highly relevant HIV risk group demonstrate a possible anatomical explanation that may contribute to the protective effect of male circumcision on HIV transmission.Randomized, controlled trials in Africa have shown that male circumcision reduces HIV-1 (HIV) acquisition in men by approximately 60%.^1,2,3 Circumcision is now recommended as a component of HIV prevention strategies, particularly in countries with endemic, generalized HIV epidemics. One of the biological explanations for the reduction in HIV acquisition could be that removal of the foreskin reduces the number of target cells for HIV.In uncircumcised men, the foreskin is retracted over the shaft during intercourse, exposing the inner mucosa to genital secretions of the partner. Genital secretions contain HIV particles, and higher viral loads of HIV in blood and semen correlate with increased risk of transmission to the sexual partner.⁴ After intercourse, the subpreputial penile moistness in uncircumcised men may also increase the risk of HIV acquisition,⁵ whereas the relative dryness in the absence of this pocket-formed area in circumcised men is a less optimal environment for HIV viability. Furthermore, the foreskin tissue is vulnerable to trauma during intercourse, providing a portal for virus entry. Inflammatory conditions of the foreskin, including sexually transmitted diseases (STDs), may also act as cofactors for HIV transmission³ (reviewed in Gray et al⁶). Even though the unkeratinized urethral meatus may still be vulnerable to HIV after circumcision, this surface area is much smaller relative to the foreskin.Many subpopulations of mononuclear phagocytes have been defined in skin and mucosal tissue based on surface markers.⁷ Among these, dendritic cells (DCs) and C-type lectin receptor (CLR) expressing CD68⁺ macrophages are likely initial target cells for HIV in the genital tract mucosa, in addition to CD4⁺ T lymphocytes.^8,9,10,11 Foreskin mucosa has indeed a high density of such cells under the lightly keratinized surface.¹² Langerhans cells (LCs) are characterized based on the expression of Langerin/CD207 (Langerin), an endocytic CLR that localizes to and forms Birbeck granules. These cells also express CD1a, a HLA-class I-like molecule that presents glycolipids.¹³ In the stratified squamous epithelium of skin and genital mucosa, the LCs overlie interstitial or submucosal DCs. So-called myeloid or conventional DCs in many tissues are often identified on the basis of high expression of HLA-DR antigen-presenting molecules and the CD11c integrin. Dermal or submucosal DCs also express pattern recognition receptors such as DC-SIGN and mannose receptor (MR). HIV has been found to bind to the CLRs Langerin, DC-SIGN, and MR, in addition to the classical HIV receptors CD4 and CCR5, which can be expressed by the same cells.Previous studies have defined target cell populations in foreskin tissue of relevance for HIV transmission.^{12,14,15,16,17,18,19} To improve the biological understanding of the decreased HIV acquisition rates after male circumcision, we have here extended previous studies with a more detailed phenotypic characterization of both potential HIV target cells as well as CLRs in foreskin tissue. We selected a highly relevant study group by obtaining cryopreserved tissue samples representing young men of high risk for HIV infection participating in the Kenyan circumcision clinical trial.² Presence of STDs was carefully controlled for because the distribution and expression of phenotypic markers of mucosal cell populations is highly affected by inflammatory activity in the tissue. This also allowed a comparison between immune markers in asymptomatic Herpes simplex virus type 2 (HSV-2) seropositive versus seronegative men.