Penile circumcision (PC) reduces HIV risk by approximately 60%. This may relate to the stochastic reduction in susceptible foreskin tissue and/or alterations in the coronal sulcus (CS) microbiome and associated inflammatory cytokines/chemokines, particularly levels of IL8. However, it is also possible that circumcision mediates protection through effects on the urethral microbiome and immune milieu. Therefore we performed a prospective analysis of the impact of PC on the microbiome and immune milieu of both the urethra and CS.
HIV-negative, STI symptom-free adult Ugandan men (n=51) undergoing elective PC were enrolled. Swabs were collected from the urethra and either the inner foreskin (pre-PC) or CS (post PC), at baseline and 12 months after PC. Multiplex ELISA quantified chemoattractant chemokines (IL-8, MIP-1b), proinflammatory cytokines (IL-1a, IL-1b) and an epithelial integrity biomarker (E-cadherin). Bacterial abundance was assessed by 16S rRNA qPCR and sequencing. The intra-individual impact of PC was assessed using the paired Wilcoxon test.
At baseline the urethra was enriched for IL-8, MIP-1b and E-cadherin, while the inner foreskin was enriched for IL-1a, IL-1b with a greater total bacterial abundance (median 27,100 vs. 1,200, gene copies/swab, p=0.001). Anaerobes made up 49% of inner foreskin bacteria, but only 26% of urethral bacteria. PC did not alter urethral IL-8 (median 1058 vs. 818 pg/ml at 12 months and baseline, respectively; p=0.057) or other chemokines/ cytokines, and urethral E-cadherin increased (155,750 vs. 111,928 pg/ml, p=0.012) suggesting reduced epithelial integrity; urethral total bacterial abundance and anaerobe abundance dropped by 5-fold and 7-fold, respectively. In contrast at the CS, where there were dramatic reductions in E-cadherin (900 vs. 15,843 pg/ml, p<0.001) and most proinflammatory chemokines/cytokines (eg: IL-8, 3 vs. 34 pg/ml; p<0.001). IL-1a was increased post-PC at the CS coupled with a 14-fold reduction in total bacterial abundance (p=0.004) and 200-fold reduction in anaerobes (p<0.001).
PC had no impact on urethral immunology and may have reduced epithelial integrity despite some reductions in total bacterial load and anaerobes; in the CS there was enhanced epithelial integrity, near total loss of anaerobes and dramatic immune alterations. This suggests that HIV protection post-PC is mediated through removal of inflamed, HIV-susceptible inner foreskin tissues rather than via the urethra.