Immune milieu and microbiome of the distal urethra in Ugandan men: impact of penile circumcision and implications for HIV susceptibility

Abstract

Background Coronal sulcus (CS) anaerobe abundance and IL-8 levels are linked to HIV acquisition, and are dramatically reduced after penile circumcision (PC). The distal urethra may be the site of some HIV acquisition before PC, and presumably most acquisition post PC. We describe the immune milieu and microbiome of the distal urethra in uncircumcised Ugandan men, and define the impact of PC. Participants consisted of HIV-negative, genital symptom-free adult Ugandan men undergoing PC (n = 51). Urethral and coronal sulcus swabs were collected at baseline and at 6- and 12-months post-PC. Soluble immune factors were quantified by multiplex ELISA, and bacterial abundance assessed by 16S rRNA qPCR and sequencing. Results At baseline, the urethra was enriched compared to the CS for most cytokines (including IL-8 and MIP-1β) and soluble E-cadherin (sE-cadherin, an epithelial disruption marker), although CS levels of IL-1α and IL-1β were higher. Baseline total bacterial abundance was ≥ 20-fold higher in the CS than the urethra (median 27,100 vs. 1200 gene copies/swab, p = 0.001), and anaerobes comprised 58% of CS bacteria vs. 42% of urethral bacteria. PC did not alter urethral IL-8 (median 806 at baseline vs. 1130 pg/ml at 12 months; p = 0.062) and urethral sE-cadherin increased (113,223 vs. 158,385 pg/ml, p = 0.009), despite five- and sevenfold drops in total bacterial and anaerobe abundance after PC, respectively. However, PC dramatically reduced CS levels of sE-cadherin (15,843 vs. 837 pg/ml, p < 0.001) and most cytokines (IL-8; 34 vs. 3 pg/ml, p < 0.001), while reducing total bacterial and anaerobe abundance by 13-fold and 60-fold, respectively (both P ≤ 0.004). Conclusions The urethra is immunologically rich with characteristics of an HIV-susceptible tissue site. However, PC had no impact on urethral immunology and may have reduced epithelial integrity, despite modest reductions in total bacteria and anaerobes, suggesting that HIV protection from PC is not mediated via immune or microbiome alterations in the urethra.

Bacterial Microbiome and Host Inflammatory Gene Expression in Foreskin Tissue

“…When examining gene expression between the participant groups with higher and lower diversity bacterial communities, we did not confirm previous findings in the penis ( 4, 6, 12 ) and vagina ( 55 ) that high bacterial diversity, particularly with anaerobic taxa, is associated with increased inflammation. While we frequently identified anaerobic taxa, individual species showed lower prevalence than in studies using surface swabs.…”

“…Previous work has shown a predominance of anaerobic species in the microbiota of swabs taken from the coronal sulcus or urethra (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11) and associated species such as Prevotella with increased mucosal inflammation, HIV target cell density and risk of HIV acquisition (4,12). Following circumcision, the surface microbiota shifts to be dominated by more aerobic species as found on other skin surfaces (6,13,14). Thus far, no data exist as to the microbiota of the foreskin itself, and its relation to tissue inflammation.…”

“…While condom use (1,2), pre-exposure prophylaxis (PrEP) (3), and medical penile circumcision (4) are effective at reducing HIV incidence in men, the contribution of the penile microbiome to these mechanisms has not been fully explored. Previous work has shown a predominance of anaerobic species in the microbiota of swabs taken from the coronal sulcus or urethra (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) and have reported associations between species such as Prevotella and increased mucosal inflammation, HIV target cell density and risk of HIV acquisition (8,16).…”

“…Following circumcision, the surface microbiota shifts to be dominated by more aerobic species as found on other skin surfaces (10,17,18). Thus far, no data exist as to the microbiota of the foreskin itself, and its relation to tissue inflammation.…”

The Penis, the Vagina and HIV Risk: Key Differences (Aside from the Obvious)

“…Specifically, penile circumcision leads to a decrease in HSV-2 and HPV in men and HPV, BV and Trichomonas vaginalis in women and also a chronic decrease in the concentration of inflammatory cytokines on the coronal sulcus [29,[112][113][114][115], and also induces an aerobic tissue environment that leads to a rapid and near-complete loss of pro-inflammatory anaerobic penile bacteria from the coronal sulcus. Interestingly, these effects are specific to the coronal sulcus since penile circumcision induces minimal change in the immunology of the urethra despite a moderate reduction in anaerobic bacteria at this site [116].…”