Mucosal‐associated invariant T (MAIT) cells are an abundant human T‐cell subset with antimicrobial properties. They can respond to bacteria presented via antigen‐presenting cells (APCs) such as macrophages, which present bacterially derived ligands from the riboflavin synthesis pathway on MR1. Moreover, MAIT cells are also highly responsive to cytokines which enhance and even substitute for T‐cell receptor‐mediated signaling. The mechanisms leading to an efficient presentation of bacteria to MAIT cells by APCs have not been fully elucidated. Here, we showed that the monocytic cell line THP‐1 and B cells activated MAIT cells differentially in response to Escherichia coli. THP‐1 cells were generally more potent in inducing IFNγ and IFNγ/TNF production by MAIT cells. Furthermore, THP‐1, but not B, cells produced TNF upon bacterial stimulation, which in turn supported IFNγ production by MAIT cells. Finally, we addressed the role of antibody‐dependent opsonization of bacteria in the activation of MAIT cells using in vitro models. We found that opsonization had a substantial impact on downstream MAIT cell activation by monocytes. This was associated with enhanced activation of monocytes and increased TNF release. Importantly, this TNF acted in concert with other cytokines to drive MAIT cell activation. These data indicate both a significant interaction between adaptive and innate immunity in the response to bacteria, and an important role for TNF in MAIT cell triggering.

Objective: HIV positive individuals, particularly men having sex with men (MSM), are at increased risk of sexually transmitted infections (STIs) at genital and extra-genital sites. Data on anorectal Ureaplasma infections are lacking. The aim of our study was to characterize anal Ureaplasma positivity among a cohort of HIV positive MSM and evaluate possible association with papillomavirus infection at the same site. Methods: Anal swab samples, collected as part of routine screening for Chlamydia trachomatis and Neisseria gonorrhea, were additionally tested for HPV genotypes as well as for Ureaplasma and Mycoplasma using nucleic acid amplification method. Results: Out of a total of 222 study participants, 195 (89%, 95% CI (84.9-93.2)) were positive for HPV, approximately three quarter being high-risk genotypes. Forty three individuals (19.4%,3)) harbored Ureaplasma spp. Infection with high-risk HPV types was significantly associated with copresence of Ureaplasma with an odds ratio (95% confidence-interval) of 2.59 (1.03-6.54), P = 0.04. Conclusion: Besides a high predominance of HPV infection, asymptomatic HIV positive MSM had a high prevalence of anal Ureaplasma positivity. Concomitant infections with high-risk HPV genotypes were common and statistically significant. The role of this co-existence as a potential risk factor for anal carcinogenesis needs further elucidation.