bims-traimu Biomed News
on Trained immunity
Issue of 2022‒07‒03
five papers selected by
Yantong Wan
Southern Medical University

  1. Immunology. 2022 Jun 25.
      Trained immunity (TRAIM) may be defined as a form of memory where innate immune cells such as monocytes, macrophages, dendritic and natural killer (NK) cells undergo an epigenetic reprogramming that enhances their primary defensive capabilities. Cross-pathogen protective TRAIM can be triggered in different hosts by exposure to live microbes or microbe-derived products such as heat-inactivated Mycobacterium bovis or with the glycan α-Gal to elicit protective responses against several pathogens. We review the TRAIM paradigm using two models representing distinct scales of immune sensitization: the whole bacterial cell and one of its building blocks, the polysaccharides or glycans. Observations point out to macrophage lytic capabilities and cytokine regulation as two key components in nonspecific innate immune responses against infections. The study of the TRAIM response deserves attention to better characterize the evolution of host-pathogen cooperation both for identifying the etiology of some diseases and for finding new therapeutic strategies. In this field, the zebrafish provides a convenient and complete biological system that could help to deepen in the knowledge of TRAIM-mediated mechanisms in pathogen-host interactions. This article is protected by copyright. All rights reserved.
    Keywords:  Cross-protection; Glycan alpha-gal; Heat-inactivated Mycobacterium bovis; Macrophages; Trained innate immunity
  2. Front Immunol. 2022 ;13 824263
      Members of the innate immune system, innate lymphoid cells (ILCs), encompass five major populations (Natural Killer (NK) cells, ILC1s, ILC2s, ILC3s, and lymphoid tissue inducer cells) whose functions include defense against pathogens, surveillance of tumorigenesis, and regulation of tissue homeostasis and remodeling. ILCs are present in the uterine environment of humans and mice and are dynamically regulated during the reproductive cycle and pregnancy. These cells have been repurposed to support pregnancy promoting maternal immune tolerance and placental development. To accomplish their tasks, immune cells employ several cellular and molecular mechanisms. They have the capacity to remember a previously encountered antigen and mount a more effective response to succeeding events. Memory responses are not an exclusive feature of the adaptive immune system, but also occur in innate immune cells. Innate immune memory has already been demonstrated in monocytes/macrophages, neutrophils, dendritic cells, and ILCs. A population of decidual NK cells characterized by elevated expression of NKG2C and LILRB1 as well as a distinctive transcriptional and epigenetic profile was found to expand during subsequent pregnancies in humans. These cells secrete high amounts of interferon-γ and vascular endothelial growth factor likely favoring placentation. Similarly, uterine ILC1s in mice upregulate CXCR6 and expand in second pregnancies. These data provide evidence on the development of immunological memory of pregnancy. In this article, the characteristics, functions, and localization of ILCs are reviewed, emphasizing available data on the uterine environment. Following, the concept of innate immune memory and its mechanisms, which include epigenetic changes and metabolic rewiring, are presented. Finally, the emerging role of innate immune memory on reproduction is discussed. Advances in the comprehension of ILC functions and innate immune memory may contribute to uncovering the immunological mechanisms underlying female fertility/infertility, placental development, and distinct outcomes in second pregnancies related to higher birth weight and lower incidence of complications.
    Keywords:   innate lymphoid cells (ILCs); Endometrium; Natural Killer cells; innate immune memory; pregnancy; trained immunity; uterus
  3. Front Cell Infect Microbiol. 2022 ;12 898030
      Fungal-bacterial intra-abdominal infections (IAI) can lead to sepsis with significant morbidity and mortality. We have established a murine model of Candida albicans (Ca) and Staphylococcus aureus (Sa) IAI that results in acute lethal sepsis. Prior intraperitoneal or intravenous inoculation with low virulence Candida dubliniensis (Cd) confers high level protection against lethal Ca/Sa IAI and sepsis. Protection via Cd immunization is associated with decreased pro-inflammatory cytokines and mediated by Gr-1+ putative myeloid-derived suppressor cells (MDSCs) representing a novel form of trained innate immunity (TII). The objective of these studies was to determine the extent of Cd-mediated TII against sepsis of broad origin and explore the potential of fungal cell wall components as abiotic immunogen alternatives to induce TII, including zymosan depleted of TLR2 activity (d-zymosan), or purified preparations of β-glucan. Immunized mice were challenged 14 days post-immunization with a lethal array of live or abiotic inducers of sepsis, including Ca/Sa, Ca/Escherichia coli (Ca/Ec), LPS or untreated zymosan. Results showed that live Cd immunization was protective against sepsis induced by Ca/Ec and zymosan, but not LPS. Similar to protection against Ca/Sa, survival was dependent on Gr-1+ cells with no role for macrophages. Among the fungal cell wall compounds as immunogens, immunization with d-zymosan and an alkali-treated form of β-glucan also resulted in significant protection against sepsis induced by Ca/Sa or Ca/Ec, but not LPS sepsis. Again, there was a strong dependence on Gr-1+ cells for protection with one exception, an added role for macrophages in the case of protection induced by alkali-treated β-glucan. Overall, these results demonstrate that immunization with Cd as well as abiotic fungal cell components are capable of Gr-1+ cell-mediated trained innate immune protection against sepsis of broad microbial origin. In addition, abiotic β-glucans represent potential alternatives to live Cd for protection against lethal polymicrobial sepsis.
    Keywords:  Candida; lipopolysaccharide (LPS); myeloid derived suppressor cell (MDSC); polymicrobial intra-abdominal infection; sepsis; trained innate immunity; zymosan
  4. RSC Chem Biol. 2022 Jun 08. 3(6): 783-793
      Macrophages play a vital role in the innate immune system, identifying and destroying unwanted cells. However, it has been difficult to attain a comprehensive understanding of macrophage protein abundance due to technical limitations. In addition, it remains unclear how changes in proteome composition are linked to phagocytic activity. In this study we developed methods to derive human macrophages and prepare them for mass spectrometry analysis in order to more-deeply understand the proteomic consequences of macrophage stimulation. Interferon gamma (IF-g), an immune stimulating cytokine, was used to induce macrophage activation, increasing phagocytosis of cancer cells by 2-fold. These conditions were used to perform comparative shotgun proteomics between resting macrophages and stimulated macrophages with increased phagocytic activity. Our analysis revealed that macrophages bias their protein production toward biological processes associated with phagocytosis and antigen processing in response to stimulation. We confirmed our findings by antibody-based western blotting experiments, validating both previously reported and novel proteins of interest. In addition to whole protein changes, we evaluated active protein synthesis by treating cells with the methionine surrogate probe homopropargylglycine (HPG). We saw increased rates of HPG incorporation during phagocytosis-inducing stimulation, suggesting protein synthesis rates are altered by stimulation. Together our findings provide the most comprehensive proteomic insight to date into primary human macrophages. We anticipate that this data can be used as a launchpoint to generate new hypotheses about innate immune function.