Paper from 16th Conference on Retroviruses and Opportunistic Infections (2009).  A pdf file of the paper is available on the website.

Background:  Male circumcision has been shown to reduce rates of HIV acquisition in men in clinical trials, but few studies have explored the biological mechanism behind this protective effect, and even these have yielded conflicting results. Utilizing advanced immunofluorescence microscopy, our laboratory has successfully visualized the penetration of infectious HIV-1 particles into explanted tissue. We report here the findings from a study of 15 adult male foreskins that confirm the ability of HIV-1 to penetrate stratified squamous epithelium and infect underlying target cells.

Conclusions:  We have visualized HIV-1 particles breaching epidermal barriers and penetrating into both inner and outer foreskin. HIV-1 was seen penetrating to depths where high numbers of Langerhans cells (LC) are found, and infected LC were clearly identified in the tissue. This supports the notion that LC can play a direct role in mediating initial infection of HIV-1 in the male genital tract. Future studies characterizing viral interactions with other target cells as well as with penile tissue will continue to contribute to a better understanding of how HIV is sexually transmitted in men.