Cell type, HIV transmission, and circumcision

This is taken from a paper I did in a capstone course for my undergrad studies. I happened to come across it recently and I thought it would be interesting to post here.

Cell type matters in HIV infection. Transmission is higher amongst homosexual men who engage in rectal intercourse where the cells there are different as compared to cells on the genitals. Thin columnar epithelium that lines the rectum is assumed to facilitate the transmission of HIV; thick stratified squamous epithelium lines the vaginal and oral mucosa and appears to transfer protective properties against HIV acquisition. Video image analysis has shown that the latter is nine to twelve times thicker than the former [2]. In addition, intercourse causes more severe trauma to the former, thus allowing viruses better access not only beyond the mucosa, but, for the rectum, a richer bed of blood vessels.

Keratinized cells are a known protector against HIV. Like the body surface of a scorpion, they prevent attachment and entry of foreign agents. In both circumcised and uncircumcised men a keratinized, stratified squamous epithelium covers the penile shaft and outer surface of the foreskin. This acts as a protective barrier against HIV. However, the inner mucosal surface of the foreskin is not keratinized [1]. Furthermore, this surface is rich with Langerhans’ cells, cells which have been associated with higher rates of HIV infection due to their expression of CD4 glycoprotein which bind directly to gpl20 on the surface of HIV [2]. Since the foreskin is pulled back during intercourse, the surface area containing Langerhans’ cells is increased, thus giving HIV more opportunities to infect a host.

Observational studies back up the hypothesis that circumcised men are less susceptible to HIV infection. A 1989 study found uncircumcised men to be over 8 times more likely to be infected versus circumcised men [3]. A 1996 Ugandan study compared HIV infection between religious groups. Once abstinence, alcohol consumption, and number of sexual partners were accounted for, it was found that the likely reason Muslim men had lower rates of HIV infection versus other religious groups was due to higher rates of circumcision [4]. A 1999 study found that circumcision amongst rural Ugandans provided significant protection against HIV infection, but only if it occurred prior to the age of 20 [5].

Another 1999 study looked interviewed close to 200 uncircumcised men and close to 200 circumcised men. Amongst non-Muslims, circumcised men were found to have a greater risk profile than uncircumcised men. That is, those who were circumcised engaged in riskier behavior and had more partners on average. However, particular sex practices and hygienic behaviors were not notably different, and so they did not account for the higher risk of HIV infection amongst uncircumcised men [6].

~~~

The paper continues with a discussion germane to the requirements for the particular assignment, so I won’t reproduce any more here. However, it should be noted that the science on the matter does continue into more recent years, resulting in most major health organizations (WHO, UNAIDS, etc) supporting male circumcision in developing nations as one valuable method in the fight against HIV/AIDS.

Citations:

1. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1127372/?tool=pubmed

2. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1383923/pdf/immunology00069-0131.pdf

3. http://www.sciencedirect.com/science/article/pii/S0140673689905898
4. Kiwanuka, Noah; Gray R., Sewankambo N.K., Serwadda D., Wawer M., Li C. (7–12 July 1996). “International Conference AIDS.”. Religion, behaviours, and circumcision as determinants of HIV dynamics in rural Uganda. Vancouver, British Columbia. Retrieved 2008-09-25

5. Kelly R, Kiwanuka N, Wawer MJ, et al (February 1999). “Age of male circumcision and risk of prevalent HIV infection in rural Uganda”. AIDS 13 (3): 399–405.

6. Bailey RC, Neema S, Othieno R (November 1999). “Sexual behaviors and other HIV risk factors in circumcised and uncircumcised men in Uganda”. J Acquir Immune Defic Syndr. 22 (3): 294–301.

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