# Gut microbiome as a potential mediator linking sexual behaviors to immune profiles in HIV-negative men who have sex with men: a multi-omics study

## TL;DR

This study shows that sexual behaviors in men who have sex with men (MSM) can change gut bacteria and immune responses, which may increase HIV risk.

## Contribution

The study reveals that the gut microbiome partially mediates how sexual behaviors influence immune profiles and HIV susceptibility in HIV-negative MSM.

## Key findings

- Receptive anal intercourse alters gut microbiome diversity and affects immune cell ratios and gene expression.
- Bilophila and Bifidobacterium are potential mediators linking sexual behaviors to immune outcomes and HIV susceptibility.
- The gut-immune axis is identified as a target for HIV prevention strategies in high-risk MSM.

## Abstract

The effects of sexual behaviors on the gut microbiome and immune system in men who have sex with men (MSM) remain unclear. Here, we conducted a multi-omics study in MSM to investigate how sexual behaviors shape gut microbiome composition and immune profiles in this population. The interplay among high-risk sexual behaviors, gut microbiome, and systemic immune activation was also explored.

HIV-negative MSM were enrolled in this study. Fecal samples were collected and subjected to 16S rRNA gene sequencing. Bulk and single-cell transcriptome sequencing of peripheral blood mononuclear cells (PBMCs) were performed to investigate the systemic immune profiles. Primary component analysis and spearman correlation analysis were used to assess the associations between gut microbiome and immune signatures. BayesPrism algorithm was applied to predict cellular composition and gene expression in individual cell types by integrating bulk RNA sequencing and sc-RNA sequencing. Causal mediation analysis evaluated the contribution of gut microbiome in linking sexual behaviors to immune outcomes.

The gut microbiome of HIV-negative MSM was dominated by Segatella. Receptive anal intercourse had the most significant impact on the gut microbiome, characterized by increased diversity, depletion of Xylanibacter, and enrichment of Holdemania. We also identified altered immune gene expression, an elevated CD8:CD4 ratio, distinctive CD4+ T cell communications, and higher expression of CXCR4 in CD4+ T cells in MSM engaged in receptive anal intercourse. Mediation analysis indicated that Bilophila potentially mediated the effects of receptive anal intercourse on CD4+ T cell proportions (P = 0.026). MSM exposed to group sex and illicit drug had elevated HIV susceptibility index, possibly mediated by Bifidobacterium (P = 0.012, P = 0.02 respectively).

Our study indicates that gut microbiome partially mediates the immunomodulatory effects of sexual behaviors, providing mechanistic insights into HIV susceptibility. These findings underscore the gut-immune axis as a potential target for HIV prevention strategies in high-risk MSM.