. Samples were stained for HIV-1 target cells with antibodies against CD4 (T cells), CD68 (macrophages), and CD1a (LCs) (Figure 1) . In all foreskin samples, quantitative immunohistochemistry revealed 0.4 to 3.1% CD4+ T cells, 1.9 to 15.6% LCs, whereas macrophages were less abundant (0.1 to 2.7%). These percentages were based on the number of brown staining cells indicating a specific immunophenotypic marker divided by the total number of nucleated cells. The overwhelming majority of the T cells were found in the submucosa whereas the majority of LCs were found in the epithelium. Additional studies using frozen tissue confirmed that the T cells were memory cells by expression of the CD45RO antigen (data not shown). The proportions of all three types of HIV-1 target cells increased with the age of the patients: CD4, r = 0.69, P = 0.007; CD68, r = 0.61, P = 0.02; CD1a, r = 0.40, P = 0.16, despite the two oldest men (ages 56 and 65 years) having lower proportions of target cells than some children. The mean proportions of each cell type were greater for adults than for children and infants. Adult men had approximately four times as many CD4+ T cells, five times as many macrophages, and 50% more LCs than children. These differences between adults and children were significant for CD4+ T cells (P < 0.01) and macrophages (P < 0.002), but not for LCs (P < 0.11). Two adult patients had notably elevated CD4+ T cells, macrophage and LC proportions: patient no. 12 had a recent history of balanitis and patient no.9 reported more than 10 lifetime sexual partners, had a history of chlamydia, and had genital warts at time of circumcision. The pediatric patient (Table 1 , no. 6) with the highest proportion of CD4+ T cells also had a documented history of balanitis.
| Table 1. Percent of Total Cells in Foreskin Tissues that are T Cells (CD4), Macrophages (CD68), and Langerhans’ Cells (CD1a) by Age of Subjects and Reported History of Infection |
| Figure 1.Immunohistochemical staining of LCs (CD1a), T cells (CD4), and macrophages (CD68) in foreskin tissue from an adult (Table 1 , no. 12) and pediatric (Table 1 , no. 8) patient. Cells expressing the appropriate antigen appear brown. Tissues (more ...) |
In a subset of individuals with foreskins that included the external surface (adults), quantitative immunohistochemistry was performed as well. As shown in Table 2 , the external foreskin mucosa contained fewer CD4+ T cells (P = 0.002) and LCs (P = 0.007) than the inner, mucosal surface as shown in Table 1 . The percentage of macrophages was similar in the external foreskin compared to the inner, mucosal surface. Further, the extent of keratinization was much greater in the external foreskin surface compared to the inner mucosal surface (data not shown). Taken together, a decrease in the number of HIV-1 target cells and an increase in the keratinization of the external foreskin suggest that susceptibility to HIV-1 infection should be significantly less in the outer compared to the inner surface of foreskin.
| Table 2. Percent of Total Cell in the External Surface of Foreskin Tissues that Are T Cells (CD4), Macrophages (CD68), and Langerhans’ Cells (CD1a) by Age of Subjects and Reported History of Infection |
Compared to the ectocervix, an HIV-1 susceptible, mucosal tissue with similar types of HIV-1 target cells, the proportion of CD1a+ LCs in adult foreskin (9.7%) is significantly greater (1.1%, P = 0.003). The proportion of LCs in pediatric foreskin was also greater than in the cervix, with a mean of 6.1% compared to 1.1% (P < 0.001). The percentage of LCs in the cervix was similar to our previous estimates of HIV-1 target cells in the cervix from a sample of 12 adult women from our Chicago cohort. 7 These data suggest that foreskin may be more susceptible to HIV-1 infection than the cervix because of an increased percentage of LCs.
HIV-1 Co-Receptor Expression in Human Foreskin
To determine chemokine receptor expression, we stained six adult foreskin specimens and six cervical samples simultaneously with phycoerythrin-labeledanti-CCR5 and fluorescein isothiocyanate-labeled anti-CXCR4 (Table 3) . In six of six adult male foreskin specimens and five of six cervical specimens, the majority of cells expressed CCR5 while a minority of cells expressed CXCR4 (Table 2) . Cells expressing the highest levels of CCR5 were found in the submucosa both on small round cells of 10-μm diameter consistent with lymphocytes and on long processes consistent with LCs (Figure 2) . The percentage of cells expressing CCR5 was significantly increased compared to the number of cells expressing CCR5 in the cervix (P < 0.05), however the percentage of cells expressing CXCR4 was greater in the foreskin but not to statistically significant levels. These data demonstrate high level expression of the necessary HIV-1 co-receptors in the foreskin. | Table 3. Percent of Total Cells in Foreskin Tissue Expressing the Major HIV-1 Co-Receptors CCR5 and CXCR4 |
| Figure 2.Representative laser confocal image of two-color immunofluorescence staining for the HIV-1 co-receptors CCR5 and CXCR4 in adult male foreskin. Red, CCR5+ cells (arrowheads); green, CXCR4+ cells (arrows). The dotted line represents the (more ...) |
Susceptibility of Human Foreskin to HIV-1 Infection
To investigate the infectivity of target cells by HIV-1, we cultured fresh, 4-mm foreskin and ectocervical biopsies in organotypic culture, infected with cell-free HIV-1, and quantified HIV-1 pol DNA copies per 1000 cells as previously described for cervical tissue culture. 8 The foreskin samples from two adults (no. 10 and no. 11) exhibited much higher levels of HIV-1 DNA than the foreskin of the 22-month-old infant (no. 3, Table 4 ). The mean HIV-1 DNA in adult foreskin tissue with no known previous exposure to sexually transmitted infections was nine times greater than in cervical tissue. Qualitative assessment of immunophenotypically identified, HIV-1-infected cells showed that infection was predominant in CD4+ T cells and in LCs at the base of the epithelial layer (Figure 3) . Consistent with our finding few HIV-1 target cells and increased keratinization in the external foreskin (Figure 4) , HIV-1 DNA was below the limits of detection in the outer surfaces of foreskin tissues infected in vitro. Consistent with the percentage of target cells and the expression of HIV-1 co-receptors on the inner mucosal surface, foreskin was more susceptible to HIV-1 infection than cervical tissue. Compatible with the chemokine receptor expression determined in this study (Table 3) and the known predilection for memory T cells and LCs to express CCR5, 10 foreskin tissue explants were far more infectable by the R5 isolate HIV-1Bal than with the X4 isolate HIV-1Lai (Table 4) . | Table 4. Quantification of HIV-1 DNA in Foreskin and Cervical Tissues 1 Day after ex Vivo Infection in Explant Culture |
| Figure 3.A: Representative laser confocal image from the inner (mucosal) surface of foreskin (Table 1 , no. 10) infected by HIV-1Bal in explant culture demonstrating infection of T cells (small, green, round cells; large arrowheads) and LCs (large, wavy, (more ...) |
| Figure 4. Representative photomicrograph of H&E-stained foreskin tissue from the outer surface (left) and the inner surface (right) of the foreskin. The extent of the keratin layer is identified by the black and white arrows. |
Discussion Repeated epidemiological studies from Africa, India, and North America have reported significant elevated risks of HIV-1 acquisition in uncircumcised compared to circumcised men. 3,4 A reason that the international health community has so far been hesitant to endorse male circumcision as a potential HIV-1 prevention strategy despite calls for its consideration 3,11,12 is that the biological mechanisms by which the presence of a foreskin increases susceptibility to HIV-1 infection in men has not been previously evaluated. Hussain and Lehner 6 previously described high densities of LCs in the mucosal surface of the foreskin, and others have suggested that the thin keratin layer on the inner mucosal surface predisposes the foreskin to infection. 13 In this study, we have confirmed that LCs are present at high densities in the mucosal epithelium of the foreskin—several times greater than in cervical tissue. Further, previously activated memory CD4+ T cells are abundant in the foreskin’s mucosal surface. These HIV-1 target cells expressed both the CCR5 and CXCR4 HIV-1 co-receptors, with CCR5 being predominant. When HIV-1 was introduced to the foreskin tissue, there was extensive infection of both the CD4+ T cells and LCs by the CCR5-using isolate HIV-1Bal, whereas infection with HIV-1Lai was ineffective in all tissue samples. Paralleling the differences in target cell proportions, the infectivity of the inner mucosal surface of the adult foreskin was several times greater than in cervical tissue. Remarkably, there was no HIV-1 infiltration of tissue taken from the outer surface of the foreskin. These results demonstrate that the inner surface of the human foreskin is highly susceptible to HIV-1 infection, much more susceptible even than the cervix, which is a known site of HIV-1 acquisition in women. 14 In addition, these results suggest that the highly keratinized outer surface of the foreskin is an unlikely site for efficient HIV-1 acquisition in men, as evidenced by the absence of detectable HIV-1 DNA in this portion of the tissue infected in explant culture. A limitation of this study is that comparable results are not available for tissue from the circumcised penis. Thus it is not possible to demonstrate that the foreskin increases risk of HIV-1 infection compared to skin from the penile shaft. In the absence of biopsies of fresh penile shaft tissue, we used the outer surface of the foreskin for comparison, and no infiltration by HIV-1 of this tissue was detected. In so far as the penile shaft is likely to be covered by a keratinized stratified squamous epithelium similar to what we found in the outer surface of the foreskin, 13 this comparison is likely to be valid. Some have speculated that the route for HIV-1 infection in the uncircumcised male is through the epithelium of the glans, which, because it is protected by the foreskin, is likely to be less keratinized in adults than the glans of the circumcised penis. However, in a study of Australian cadavers, the epithelia of the glans in circumcised and uncircumcised men were equally keratinized. 2 A logical but as yet unproven conclusion concerning routes of HIV-1 acquisition in the circumcised penis is that infection occurs through the urethral mucosa or through disruptions of the penile shaft epithelia caused by genital ulcer disease or trauma. The two adult patients who had recent penile infections (patients no. 9 and no. 12) had highly elevated proportions of HIV-1 target cells. Because the levels of infiltration by HIV-1 of foreskin tissue in this study paralleled the levels of target cells in the tissue, active infection with sexually transmitted infections or other pathogens would likely elevate target cell activity and result in increased risk of HIV-1 acquisition. This is consistent with epidemiological evidence that infection with a sexually transmitted infection increases risk of HIV-1 acquisition more in uncircumcised than in circumcised men. 15 That HIV-1 target cells increased with age in the patients suggests that there is a developmental trajectory of the immune response. However, these findings are also consistent with the hypothesis that exposure to pathogens stimulates increases in target cell recruitment. The levels of CD4+ T cells, macrophages, and LCs were variable in the children, and the highest levels of CD4+ T cells and LCs were in sexually active adult men. Remarkably, the two oldest patients, who reported little sexual activity, had target cell levels comparable to children. Previous studies report HIV-1 in women to be genetically heterogeneous, but the virus detected in men soon after sexual contact is homogeneous. 16 Here, we have demonstrated that, at least in this small sample, the adult male foreskin contains much greater numbers of LCs and memory T cells than the ectocervix of women. These two cell types have previously been demonstrated to express almost exclusively CCR5 on their surfaces, 10,17 a finding also supported by results in this study. The predominant expression of CCR5 in foreskin tissue is consistent with infection by homogeneously macrophage-tropic isolates of HIV-1. Further, recent studies have demonstrated that the interactions of dendritic cells and T cells through the lectin-receptor DCSIGN enhance productive HIV-1 infection and dissemination of the virus to regional lymph nodes. 18 A recent study of 187 HIV-1 serodiscordant couples in Uganda in which females were infected and males were initially uninfected, reported that, during just less than 2 years of follow-up, 40 of 137 uncircumcised men seroconverted, while 0 of 50 circumcised men seroconverted. 19 Those results combined with our findings showing vigorous infiltration by HIV-1 of target cells in foreskin tissue suggest that the presence of a foreskin is a true biological cause of increased HIV-1 susceptibility in uncircumcised men. The implications of these findings are that strong consideration should be given to integrating male circumcision information and services with the currently limited armamentarium of other HIV-1 prevention tools. This will require considerations of the acceptability and operational feasibility of introducing safe, affordable services in currently noncircumcising societies where most infections are transmitted heterosexually. 20 Attention must be given to counseling parents and men against increasing sexual risk behaviors in the belief that circumcision fully protects against HIV-1 acquisition. In addition, the development of topically active agents capable of blocking HIV-1 binding sites and that can be applied to the penis or vagina should proceed. 21 |
|
References 1. : Joint United Nations Programme on HIV-1/AIDS (UNAIDS) and World Health Organization (WHO): AIDS Epidemic Update—December 2001 2002 UNAIDS, Geneva . 2. Szabo R, Short R: How does male circumcision protect against HIV-1 infection? Br Med J 2000, 320:1592-1594 [PubMed]. 3. Bailey RC, Plummer FA, Moses S: Male circumcision and HIV prevention: current knowledge and future research directions. Lancet Infect Dis 2002, 1:223-231. 4. Moses S, Bailey R, Ronald A: Male circumcision: assessment of health benefits and risks. Sexually Transmitted Infections 1998, 74:368-373 [PubMed]. 5. Weiss HA, Quigley MA, Hayes RJ: Male circumcision and risk of HIV-1 infection in sub-Saharan Africa: a systematic review and meta-analysis. AIDS 2000, 14:2261-2370. 6. Hussain L, Lehner T: Comparative investigation of Langerhans’ cells and potential receptors for HIV-1 in oral, genitourinary and rectal epithelia. Immunology 1995, 85:475-484 [PubMed]. 7. Patterson BK, Landay A, Anderson Brown C, Behbanhani H, Jiyamapa D, Burki Z, Stanislawski D, Czerniewski M, Garcia P: Repertoire of chemokine receptor expression in the female genital tract. Am J Pathol 1998, 153:481-490 [PubMed]. 8. Collins K, Patterson BK, Naus G, Landers D, Gupta P: Development of an in vitro organ culture model to study transmission of HIV-1 in the female genital tract. Nat Med 2000, 6:475-479 [PubMed]. 9. Behbahani H, Popek E, Garcia P, Andersson J, Spetz A-L, Landay A, Flener Z, Patterson BK: Up-regulation of CCR5 expression in the placenta is associated with human immunodeficiency virus-1 vertical transmission. Am J Pathol 2000, 157:1811-1818 [PubMed]. 10. Bleul CC, WU L, Hoxie JA, Springer TA, Mackay CR: The HIV coreceptors CXCR4, and CCR5 are differentially expressed and regulated on human T-lymphocytes. Proc Natl Acad Sci USA 1997, 94:1925-1930 [PubMed]. 11. Fink A: A possible explanation for heterosexual male infection with AIDS. N Engl J Med 1986, 314:1167. 12. Buve A, Auvert B, Langarde E, Kahindo M, Hayes R, Carael M: Male circumcision and HIV-1 spread in sub-Saharan Africa. In Abstracts, XIII International Conference on AIDS. (MoOrC192). Durban, South Africa, August, 2000. 13. Fussell EN, Kaak MB, Cherry R, Roberts J: Adherence of bacteria to human foreskin. J Urol 1988, 140:997-1001 [PubMed]. 14. Alexander NJ: Sexual transmission of human immunodeficiency virus: virus entry into the male and female genital tract. Fertil Steril 1990, 54:1-18 [PubMed]. 15. Cameron D, Simonsen J, D’Costa L, Ronald A, Maitha G, Gakinya M, Cheang M, Ndinya-Achola J, Piot P, Brunham R, Plummer F: Female to male transmission of human immunodeficiency virus type 1: risk factors for seroconversion. Lancet 1989, 2:403-407 [PubMed]. 16. Long EM, Martin HL, Kreiss JK, Rainwater SMJ, Lavreys L, Jackson DJ, Rakwar J, Mandaliya K, Overbaugh J: Gender differences in HIV-1 diversity at time of infection. Nat Med 2000, 6:71-75 [PubMed]. 17. Zaitseva M, Blauvelt A, Lee S, Lapham CK, Klaus-Kovtun V, Mostowski H, Manischewitz J, Golding H: Expression and function of CCR5 and CXCR4 on human Langerhan’s cells and macrophages: implications for HIV-1 primary infection. Nat Med 1997, 3:1369-1375 [PubMed]. 18. Geijtenbeek T, Kwon D, Torensma R, van Vliet S, van Duijnhoven G, Middel J, Cornelissen I, Nottet H, Kewalromani V, Littman D, Figdor C, van Kooyk Y: DC-SIGN, a dendritic cell-specific HIV-1 binding protein that enhances trans-infection of T cells. Cell 2000, 100:587-597 [PubMed]. 19. Quinn T, Wawer M, Sewankambo N, Serwadda D, Li C, Wabwire-Mangen F, Meehan M, Lutalo T, Gray RH: For the Rakai Project Study Group. Viral load and heterosexual transmission of human immunodeficiency virus type 1. N Engl J Med 2000, 342:921-929 [PubMed]. 20. Bailey RC, Muga R, Poulussen, R. Trial intervention introducing male circumcision to reduce HIV-1/STD infections in Nyanza Province, Kenya: baseline results. In Abstract Book, Volume I, XIII International Conference on AIDS, Durban, South Africa, August, 2000. 21. UNAIDS: Microbicides for HIV infection: UNAIDS technical update. UNAIDS Best Practice Collection: Technical Update. Geneva, UNAIDS, April, 1998. |
| |