Several studies have shown that HIV infection is associated with alterations in gut microbiota composition. Recent findings from a European cohort suggest that the main alterations are associated with sexual behavior of men who have sex with men (MSM) rather than with infection itself. Given that MSM are at higher risk of becoming infected with HIV, it is of importance to understand the impact of MSM-associated microbiota on immune cells in the gut as it relates to disease and HIV transmission.
The fecal microbiota of a U.S. cohort (n=210), including HIV-negative high-risk MSM (n=42) and low-risk heterosexual men (n=22), were analyzed using 16S rRNA gene sequencing. Feces from three representative MSM and three representative heterosexual men were used to gavage gnotobiotic mice (n≥4 mice per fecal sample), and mice were analyzed for immune activation following colonization. Bacterial cells were isolated from original fecal samples (n=8 MSM, 8 heterosexual men) using density centrifugation, and used to stimulate human peripheral blood mononuclear cells (PBMCs) and gut lamina propria cells (LPMCs). After stimulation, PBMC were analyzed for activation, and LPMCs were infected with HIV[sub]bal[/sub] and stained for p24 expression at 5 days post infection.
Within our cohort of HIV-negative MSM in the U.S., the majority of subjects harbor a Prevotella-rich/Bacteroides-poor microbiome, similar to that of HIV-infected subjects and compositionally distinct from low risk HIV-negative subjects which harbor a Prevotella-poor/Bacteroides-rich microbiome. Following fecal microbial transplantation to gnotobiotic mice, T cells in the lamina propria exhibited higher CD69 expression (p=0.017), and macrophages in the mesenteric lymph node showed higher CD86 expression (p=0.006), when mice were colonized with feces from MSM. Stimulation of human PBMCs with bacteria isolated from MSM feces resulted in higher levels of HLA-DR+ CD38+ CD4+ T cells when compared with PBMCs stimulated with fecal bacteria from heterosexual men (p=0.001). Finally, stimulation of LPMCs with MSM-associated bacteria induced higher infection levels with HIVbal compared with LPMCs stimulated with fecal bacteria from heterosexual men (p=0.008).
Our data support previous findings of gut microbiome compositional differences between MSM and heterosexual men, and suggest that microbiota of MSM may play a role in increasing their risk to HIV infection by inducing immune activation.