Interactions between pattern recognition receptors (PRRs) shape innate immune responses to particular classes of pathogens. Here, we review interactions between TLRs and nucleotide‐binding ...oligomerization domain 1 and 2 (NOD1 and NOD2) receptors, two major groups of PRRs involved in innate recognition of bacteria. Most of experimental data both in vitro and in vivo suggest that NODs and TLRs synergize with each other at inducing the production of cytokines and antimicrobial peptides. Molecular mechanisms of this synergy remain poorly understood, although several scenarios can be proposed: (i) direct interactions of signaling pathways downstream of NODs and TLRs; (ii) mutual transcriptional regulation of unique components of NOD‐dependent and TLR‐dependent signaling pathways; and (iii) interactions at the post‐transcriptional level. Potential practical implications of NOD‐TLR synergy are dual. In sepsis, where synergistic effects probably contribute to excessive proinflammatory cytokine production, blockade of NOD1, and/or NOD2 in addition to TLR4 blockade may be required to achieve therapeutic benefit. On the other hand, synergistic combinations of relatively small doses of NOD and TLR agonists administered before infection could be used to boost innate resistance against bacterial pathogens.
NOD1/NOD2 and TLRs synergize at induction of innate immune responses, which can be beneficial (boosting protective immunity) or deleterious (in sepsis).
Upon activation with pathogen-associated molecular patterns, metabolism of macrophages and dendritic cells is shifted from oxidative phosphorylation to aerobic glycolysis, which is considered ...important for proinflammatory cytokine production. Fragments of bacterial peptidoglycan (muramyl peptides) activate innate immune cells through nucleotide-binding oligomerization domain (NOD) 1 and/or NOD2 receptors. Here, we show that NOD1 and NOD2 agonists induce early glycolytic reprogramming of human monocyte-derived macrophages (MDM), which is similar to that induced by the Toll-like receptor 4 (TLR4) agonist lipopolysaccharide. This glycolytic reprogramming depends on Akt kinases, independent of mTOR complex 1 and is efficiently inhibited by 2-deoxy-d-glucose (2-DG) or by glucose starvation. 2-DG inhibits proinflammatory cytokine production by MDM and monocyte-derived dendritic cells activated by NOD1 or TLR4 agonists, except for tumor necrosis factor production by MDM, which is inhibited initially, but augmented 4 h after addition of agonists and later. However, 2-DG exerts these effects by inducing unfolded protein response rather than by inhibiting glycolysis. By contrast, glucose starvation does not cause unfolded protein response and, in normoxic conditions, only marginally affects proinflammatory cytokine production triggered through NOD1 or TLR4. In hypoxia mimicked by treating MDM with oligomycin (a mitochondrial ATP synthase inhibitor), both 2-DG and glucose starvation strongly suppress tumor necrosis factor and interleukin-6 production and compromise cell viability. In summary, the requirement of glycolytic reprogramming for proinflammatory cytokine production in normoxia is not obvious, and effects of 2-DG on cytokine responses should be interpreted cautiously. In hypoxia, however, glycolysis becomes critical for cytokine production and cell survival.
Interactions between pattern-recognition receptors shape innate immune responses to pathogens. NOD1 and TLR4 are synergistically interacting receptors playing a pivotal role in the recognition of ...Gram-negative bacteria. However, mechanisms of their cooperation are poorly understood. It is unclear whether synergy is produced at the level of signaling pathways downstream of NOD1 and TLR4 or at more distal levels such as gene transcription. We analyzed sequential stages of human macrophage activation by a combination of NOD1 and TLR4 agonists (
-acetyl-d-muramyl-l-alanyl-d-isoglutamyl-meso-diaminopimelic acid M-triDAP and LPS, respectively). We show that events preceding or not requiring activation of transcription, such as activation of signaling kinases, rapid boost of glycolysis, and most importantly, nuclear translocation of NF-κB, are regulated nonsynergistically. However, at the output of the nucleus, the combination of M-triDAP and LPS synergistically induces expression of a subset of M-triDAP- and LPS-inducible genes, particularly those encoding proinflammatory cytokines (
,
,
,
, and
). This synergistic response develops between 1 and 4 h of agonist treatment and requires continuous signaling through NOD1. The synergistically regulated genes have a lower basal expression and higher inducibility at 4 h than those regulated nonsynergistically. Both gene subsets include NF-κB-inducible genes. Therefore, activation of the NF-κB pathway does not explain synergistic gene induction, implying involvement of other transcription factors. Inhibition of IKKβ or p38 MAPK lowers agonist-induced
mRNA expression but does not abolish synergy. Thus, nonsynergistic activation of NOD1- and TLR4-dependent signaling pathways results in the synergistic induction of a proinflammatory transcriptional program.
In a prospective study involving 5340 individuals, humoral and cellular responses revealed magnitude-dependent protection from COVID-19. Antibodies alone significantly decreased infection rates; ...isolated cellular response provided an intermediate level of protection. The lowest COVID-19 incidence was in the double-positive group.
Abstract
Background
During the ongoing coronavirus disease 2019 (COVID-19) pandemic, many individuals were infected with and have cleared the virus, developing virus-specific antibodies and effector/memory T cells. An important unanswered question is what levels of T-cell and antibody responses are sufficient to protect from the infection.
Methods
In 5340 Moscow residents, we evaluated anti–severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunoglobulin M (IgM)/immunoglobulin G (IgG) titers and frequencies of the T cells specific to the membrane, nucleocapsid, and spike proteins of SARS-CoV-2, using interferon gamma (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) assay. Additionally, we evaluated the fractions of virus-specific CD4+ and CD8+ T cells using intracellular staining of IFN-γ and interleukin 2 followed by flow cytometry. We analyzed the COVID-19 rates as a function of the assessed antibody and T-cell responses, using the Kaplan–Meier estimator method, for up to 300 days postinclusion.
Results
We showed that T-cell and antibody responses are closely interconnected and are commonly induced concurrently. Magnitudes of both responses inversely correlated with infection probability. Individuals positive for both responses demonstrated the highest levels of protectivity against the SARS-CoV-2 infection. A comparable level of protection was found in individuals with antibody response only, whereas the T-cell response by itself granted only intermediate protection.
Conclusions
We found that the contribution of the virus-specific antibodies to protection against SARS-CoV-2 infection is more pronounced than that of the T cells. The data on the virus-specific IgG titers may be instructive for making decisions in personalized healthcare and public anti–COVID-19 policies.
Clinical Trials Registration. NCT04898140.
During the ongoing coronavirus disease COVID-19 pandemic, many individuals were infected with and have cleared the virus, developing virus-specific antibodies and effector/memory T cells. An ...important unanswered question is what levels of T cell and antibody responses are sufficient to protect from the infection.
In 5340 Moscow residents, we evaluated anti-SARS-CoV-2 IgM/IgG titers and frequencies of the T cells specific to the membrane, nucleocapsid, and spike proteins of SARS-CoV-2, using IFNγ ELISpot assay. Additionally, we evaluated the fractions of virus-specific CD4+ and CD8+ T cells using intracellular staining of IFNγ and IL2 followed by flow cytometry. We analyzed the COVID-19 rates as a function of the assessed antibody and T cell responses, using the Kaplan-Meyer estimator method, for up to 300 days post-inclusion.
We showed that T cell and antibody responses are closely interconnected and are commonly induced concurrently. Magnitudes of both responses inversely correlated with infection probability. Individuals positive for both responses demonstrated the highest levels of protectivity against the SARS-CoV-2 infection. A comparable level of protection was found in individuals with antibody response only, while the T cell response by itself granted only intermediate protection.
We found that the contribution of the virus-specific antibodies to protection against the SARS-CoV-2 infection is more pronounced than that of the T cells. The data on the virus-specific IgG titers may be instructive for making decisions in personalized health care and public anti-COVID-19 policies.
The ability of biological fluids to kill microbes is an important feature of the human immune system. Following incubation of fluorescein isothiocyanate-labeled Staphylococcus aureus with biological ...specimens and subsequent staining with propidium iodide, the proportions of killed bacteria were estimated by flow cytometry. FACScan is a simple, quick and reliable method to evaluate bactericidal activity of biological fluids. The results of the cytometric method correlated well with the results of the classic microbiological method. The proposed method is highly informative for evaluating bactericidal activity of sera in immunocompromised patients.
The killing of microorganisms by neutrophils causes degranulation of azurophilic, specific, and gelatinase granules into the formed phagolysosomes. During the degranulation process, increased surface ...expression of CD63 (localized in the azurophilic granules of resting neutrophils) and CD66b/CD67 (from specific granules) can be detected. This results from the fusion of the granule membrane, containing these markers, with a plasma membrane. Release of granule content into the phagolysosomes or the extracellular environment occurs not only upon proper cell activation but also upon tissue injury. We compared expression of degranulation markers on neutrophils from chronic granulomatous disease (CGD) patients and healthy volunteers. Surface expression of CD63 in non-stimulated and phorbol 12-myristate 13-acetate (PMA)-stimulated neutrophils, bactericidal activity of serum, and alpha-defensins level (HNP 1–3) in plasma of CGD patients were significantly higher in comparison with healthy volunteers. At the same time, the levels of intracellular HNP 1–3 in CGD neutrophils were lower than in normal neutrophils. Thus, our data revealed augmented degranulation of azurophilic neutrophil granules in CGD, which might play a role in tissue destruction observed in this disease.
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