Trichomonas vaginalis: Pathogenesis, Symbiont Interactions, and Host Cell Immune Responses

• Published in: Trends in parasitology 2018-08, Vol.34 (8), p.683-693
• Main Authors: Mercer, Frances, Johnson, Patricia J.
• Format: Article
• Language: English
• Subjects: cytokines; Humans; immunity; Immunity, Cellular - immunology; microbiota; neutrophils; pathogenesis; Symbiosis; Trichomonas Infections - immunology; Trichomonas Infections - pathology; Trichomonas vaginalis; Trichomonas vaginalis - immunology
• ISSN: 1471-4922; 1471-5007
• DOI: 10.1016/j.pt.2018.05.006

The parasite Trichomonas vaginalis (Tv) causes a highly prevalent sexually transmitted infection. As an extracellular pathogen, the parasite mediates adherence to epithelial cells to colonize the human host. In addition, the parasite interfaces with the host immune system and the vaginal microbiota. Modes of Tv pathogenesis include damage to host tissue mediated by parasite killing of host cells, disruption of steady-state vaginal microbial ecology, and eliciting inflammation by activating the host immune response. Recent Tv research has uncovered new players that contribute to multifactorial mechanisms of host–parasite adherence and killing, and has examined the relationship between Tv and vaginal bacteria. Mechanisms that may lead to parasite recognition and killing, or the evasion of host immune cells, have also been revealed. New players in the multifactorial process of host–parasite interactions have been identified, including parasite-secreted vesicles (exosomes) and various surface and secreted proteases and effector proteins. Tv is associated with disruption of the vaginal microbiota; specific interactions with vaginal microbes representative of the healthy and disrupted-state are being examined. Neutrophils were found to kill Tv using a novel antimicrobial mechanism, trogocytosis. Identification of the mechanisms immune cells use to kill Tv allows analysis of modes that the parasite might use to evade immune elimination. A holistic view of how Tv modulates host immunity is emerging. New roles for three microbial symbionts, a parasite-derived cytokine mimic (TvMIF), exosomes, a surface glycoconjugate, and the selective targeting of lymphocyte populations for killing have been revealed.