Human MAIT cell cytolytic effector proteins synergize to overcome carbapenem resistance in Escherichia coli

Abstract

Mucosa-associated invariant T (MAIT) cells are abundant antimicrobial T cells in humans and recognize antigens derived from the microbial riboflavin biosynthetic pathway presented by the MHC-Ib-related protein (MR1). However, the mechanisms responsible for MAIT cell antimicrobial activity are not fully understood, and the efficacy of these mechanisms against antibiotic resistant bacteria has not been explored. Here, we show that MAIT cells mediate MR1-restricted antimicrobial activity against Escherichia coli clinical strains in a manner dependent on the activity of cytolytic proteins but independent of production of pro-inflammatory cytokines or induction of apoptosis in infected cells. The combined action of the pore-forming antimicrobial protein granulysin and the serine protease granzyme B released in response to T cell receptor (TCR)-mediated recognition of MR1-presented antigen is essential to mediate control against both cell-associated and free-living, extracellular forms of E. coli. Furthermore, MAIT cell-mediated bacterial control extends to multidrug-resistant E. coli primary clinical isolates additionally resistant to carbapenems, a class of last resort antibiotics. Notably, high levels of granulysin and granzyme B in the MAIT cell secretomes directly damage bacterial cells by increasing their permeability, rendering initially resistant E. coli susceptible to the bactericidal activity of carbapenems. These findings define the role of cytolytic effector proteins in MAIT cell-mediated antimicrobial activity and indicate that a1111111111 a1111111111 a1111111111 a1111111111 a1111111111

Mucosal-Associated Invariant T (MAIT) Cells Are Highly Activated and Functionally Impaired in COVID-19 Patients

“…In contrast, expression of TNFα and IL-17A was similar in MAIT cells from patients with mild and patients with severe COVID-19, irrespective of the way of stimulation ( Figure S4B ). It has been shown previously that MAIT cells develop a cytotoxic profile characterised by expression of cytolytic proteins, such as granzyme B and perforin, upon stimulation [ 14 , 30 ], thereby rendering them able to kill bacterially infected cells [ 14 , 15 , 16 , 17 ]. We therefore analysed the expression of granzyme B and perforin in MAIT cells from COVID-19 patients and healthy controls upon in vitro stimulation with E. coli , or IL-12/IL-18, respectively.…”

“…One might even speculate that this hints towards beginning MAIT cell exhaustion due to chronic activation in vivo. MAIT cells are considered important antimicrobial effectors and have been shown to contribute to controlling bacterial infections both by recruitment of other immune cell populations and by lysis of bacterially infected cells [ 14 , 15 , 16 , 17 , 43 , 44 ]. Our data suggest that the antibacterial effector function of MAIT cells might be impaired in COVID-19.…”

“…Upon activation, MAIT cells express the pro-inflammatory cytokines IFNγ, TNFα and IL-17A. Moreover, they can eliminate bacterially infected cells by secretion of cytolytic proteins [ 14 , 15 , 16 , 17 ]. Hence, MAIT cells have been shown to protect against pulmonary infection with various bacteria (reviewed in [ 18 ]) and to inflict IL-17A-mediated inflammation in pulmonary infection [ 19 ].…”

Expansion of donor-unrestricted MAIT cells with enhanced cytolytic function suitable for TCR redirection

“…The metabolites recognized by MAIT cells are byproducts of the riboflavin biosynthesis pathway expressed by diverse species of bacteria, mycobacteria, and fungi ( 12 ); therefore, in association with their location at sites of pathogen entry, MAIT cells are viewed as early sentinels responding to microbial infections. In response to antigen, MAIT cells produce proinflammatory cytokines, such as IFN-γ, TNF, and IL-17A, and can release cytolytic effector molecules, including granzymes and perforin, leading to the lysis of the infected cells, the inhibition of bacterial growth, and the shaping of the local immune response ( 9 , 13 – 15 ). MAIT cells can also be activated in a TCR- and MR1-independent way via the proinflammatory cytokines IL-12 and IL-18, triggering mainly IFN-γ production ( 16 – 18 ).…”

Pathophysiological Roles of Mucosal-Associated Invariant T Cells in the Context of Gut Microbiota-Liver Axis

“…Additionally, because of their innate-like nature, they are activated by the proinflammatory cytokines interleukin (IL)-12 and IL-18 in a TCR-independent manner [ 16 ]. Upon activation, MAIT cells are involved in immune responses in various ways, including expression of activation markers CD69 and CD25, secretion of proinflammatory cytokines such as interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), and IL-17 as well as exerting cytotoxic properties via granzyme B and perforin secretion [ 17 , 18 , 19 ]. When they were first discovered, MAIT cells were localized in the lamina propria of the intestinal mucosa in relative abundance [ 7 ].…”