Interacting effects of HIV infection and sexual behavior on the male gut microbiota and host immune-inflammatory responses

Both human immunodeficiency virus (HIV) infection and sexual behaviors, particularly among men who have sex with men (MSM), are known to influence gut microbial composition and immune regulation. However, their interacting effects on the gut microbiome and systemic immune-inflammatory responses remain unclear. This cross-sectional study included 378 adult men classified into 4 groups: HIV-positive MSM (PMSM), HIV-positive men who have sex with women (PMSW), HIV-negative MSM (NMSM), and HIV-negative MSW (NMSW). Fecal samples were analyzed via 16S rRNA (V3-V4) sequencing, and microbial diversity and composition were analyzed using QIIME2, LEfSe, and MaAsLin2. Immune and inflammatory markers (CD4 count, CD4/CD8 ratio, IL-1β, IL-10, hsCRP, D-lactate, and IP-10) were quantified and correlated with microbial features. HIV infection and sexual behavior each significantly shaped gut microbial diversity and composition, with observable interaction effects. Alpha diversity indices (Shannon and Simpson) were highest in the PMSM group ( p < 0.001), and beta diversity differed significantly among all four groups (PERMANOVA, p = 0.001). Prevotella , Succinivibrio , and Alloprevotella were enriched in MSM compared with MSW, whereas Bacteroides and Ruminococcus gnavus group predominated in MSW. HIV infection was associated with enrichment of pro-inflammatory and opportunistic genera ( Succinivibrio , Fusobacterium , Escherichia–Shigella ) and depletion of short-chain fatty acid (SCFA)-producing genera ( Faecalibacterium , Blautia , Lachnospira ). Significant interaction effects were observed for Erysipelatoclostridium (positive) and Butyricicoccus (negative), indicating synergistic modulation of the microbiome by HIV and sexual behavior. Reduced SCFA producers correlated with lower CD4/CD8 ratios and elevated IL-1β, IP-10, and D-lactate levels, reflecting impaired mucosal barrier function and chronic immune activation. HIV infection and MSM sexual behavior exert independent and synergistic effects on the gut microbiome. Loss of SCFA-producing commensals and expansion of pro-inflammatory taxa may contribute to mucosal barrier disruption and systemic inflammation in HIV-positive men. These findings suggest the gut microbiome could be a potential therapeutic target to mitigate immune activation and enhance mucosal health in people living with HIV.