Intestinal immune responses to commensal and pathogenic protozoa

Abstract

The physical barrier of the intestine and associated mucosal immunity maintains a delicate homeostatic balance between the host and the external environment by regulating immune responses to commensals, as well as functioning as the first line of defense against pathogenic microorganisms. Understanding the orchestration and characteristics of the intestinal mucosal immune response during commensal or pathological conditions may provide novel insights into the mechanisms underlying microbe-induced immunological tolerance, protection, and/or pathogenesis. Over the last decade, our knowledge about the interface between the host intestinal mucosa and the gut microbiome has been dominated by studies focused on bacterial communities, helminth parasites, and intestinal viruses. In contrast, specifically how commensal and pathogenic protozoa regulate intestinal immunity is less well studied. In this review, we provide an overview of mucosal immune responses induced by intestinal protozoa, with a major focus on the role of different cell types and immune mediators triggered by commensal (Blastocystis spp. and Tritrichomonas spp.) and pathogenic (Toxoplasma gondii, Giardia intestinalis, Cryptosporidium parvum) protozoa. We will discuss how these various protozoa modulate innate and adaptive immune responses induced in experimental models of infection that benefit or harm the host.

Uncovering the diversity of pathogenic invaders: insights into protozoa, fungi, and worm infections

“…Additionally, this type of hypersensitivity is linked to several complications, such as edoema, blood hyperviscosity, and hypotension. Similar kinds of humoral immune responses are also observed in other infections caused by protozoa that are listed in Table 1 ( Gurung and Kanneganti, 2016 ; Sardinha-Silva et al, 2022 ).…”

Giardia intestinalisreshapes mucosal immunity toward a Type 2 response that attenuates inflammatory bowel-like diseases

“…Giardiasis is one of the most prevalent enteric diseases associated with stunting in children under 2 years of age (Rogawski et al, 2018), with prevalence estimates ranging from 2% to in excess of 30% from high and low-middle income countries, respectively (Dixon, 2021). More recently referred to as a commensal pathogen (Sardinha-Silva et al ., 2022), the degree to which Giardia persists as a natural member of the host gut microbiome has not been systematically studied. To investigate the prevalence of asymptomatic carriage of Giardia infection in susceptible school-aged children, we screened 664 fecal samples collected across 6 health districts along a longitudinal transect from the North to the South of Nigeria that comprised vastly different ecotypes and was a mix of rural and semi-urban sites (Supp.Fig.1 and Table 1).…”

The commensal protistTritrichomonas musculusexhibits a dynamic life cycle that induces extensive remodeling of the gut microbiota

“…Research into host-associated microbiomes has established the critical role of gut bacteria in health and disease 1,2 . Emerging data supports an appreciable presence of gut-dwelling protists with host immunomodulatory capabilities and influence over resident bacterial communities, suggesting these microbes are essential players in organizing the gut environment 3–7 . Studies in this discipline are in their infancies however and lack understanding of both the ability of protists to colonize and persist and protist:bacterial cross-talk in the context of host immunity.…”

“…Intestinal microbiota are key regulators of host health and the development of disease 1,2 . The majority of studies currently address roles of bacteria and fungi, however emerging data supports an appreciable presence of protists in the gut [3][4][5] . These include species considered commensals, diarrheagenic parasites and pathobionts that exert influential roles on resident bacterial communities.…”