ABSTRACT
With a global tally of more than 500 million cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections to date, there are growing concerns about the post-acute sequelae of SARS-CoV-2 infection (PASC), also known as long COVID. Recent studies suggest that exaggerated immune responses are key determinants of the severity and outcomes of the initial SARS-CoV-2 infection as well as subsequent PASC. The complexity of the innate and adaptive immune responses in the acute and post-acute period requires in-depth mechanistic analyses to identify specific molecular signals as well as specific immune cell populations which promote PASC pathogenesis. In this review, we examine the current literature on mechanisms of immune dysregulation in severe COVID-19 and the limited emerging data on the immunopathology of PASC. While the acute and post-acute phases may share some parallel mechanisms of immunopathology, it is likely that PASC immunopathology is quite distinct and heterogeneous, thus requiring large-scale longitudinal analyses in patients with and without PASC after an acute SARS-CoV-2 infection. By outlining the knowledge gaps in the immunopathology of PASC, we hope to provide avenues for novel research directions that will ultimately lead to precision therapies which restore healthy immune function in PASC patients.
Subject(s)
COVID-19 , Post-Acute COVID-19 Syndrome , Humans , COVID-19/complications , Disease Progression , SARS-CoV-2ABSTRACT
Tuberculosis (TB) is a serious global disease. The fatality rate attributed to TB is among the highest of infectious diseases, with approximately 2 million deaths occurring per year worldwide. Identification of individuals infected with Mycobacterium tuberculosis and screening of their immediate contacts is crucial for controlling the spread of TB. Current methods for detection of M. tuberculosis infection are not efficient, in particular, for testing large numbers of samples. We report a novel and efficient multiplex microbead immunoassay (MMIA), based on Luminex technology, for profiling antibodies to M. tuberculosis. Microbead sets identifiable by unique fluorescence were individually coated with each of several M. tuberculosis antigens and tested in multiplex format for antibody detection in the experimental nonhuman primate model of TB. Certain M. tuberculosis antigens, e.g., ESAT-6, CFP-10, and HspX, were included to enhance the specificity of the MMIA, because these antigens are absent in nontuberculous mycobacteria and the vaccine strain Mycobacterium bovis bacillus Calmette-Guérin. The MMIA enabled simultaneous detection of multiple M. tuberculosis plasma antibodies in several cohorts of macaques representing different stages of infection and/or disease. Antibody profiles were defined in early and latent/chronic infection. These proof-of-concept findings demonstrate the potential clinical use of the MMIA. In addition, the MMIA serodetection system has a potential for mining M. tuberculosis open reading frames (about 4,000) to discover novel target proteins for the development of more-comprehensive TB serodiagnostic tests.
Subject(s)
Antibodies, Viral/blood , Antigens, Bacterial/immunology , Immunoassay/methods , Microspheres , Mycobacterium tuberculosis/immunology , Tuberculosis/diagnosis , Animals , Bacterial Proteins/immunology , Fluorescence , Humans , Macaca fascicularis , Macaca mulatta , Tuberculosis/immunology , Tuberculosis/microbiologyABSTRACT
Mycobacterium tuberculosis, a Gram-positive bacterium, encodes a secreted Dsb-like protein annotated as Mtb DsbE (Rv2878c, also known as MPT53). Because Dsb proteins in Escherichia coli and other bacteria seem to catalyze proper folding during protein secretion and because folding of secreted proteins is thought to be coupled to disulfide oxidoreduction, the function of Mtb DsbE may be to ensure that secreted proteins are in their correctly folded states. We have determined the crystal structure of Mtb DsbE to 1.1 A resolution, which reveals a thioredoxin-like domain with a typical CXXC active site. These cysteines are in their reduced state. Biochemical characterization of Mtb DsbE reveals that this disulfide oxidoreductase is an oxidant, unlike Gram-negative bacteria DsbE proteins, which have been shown to be weak reductants. In addition, the pK(a) value of the active site, solvent-exposed cysteine is approximately 2 pH units lower than that of Gram-negative DsbE homologs. Finally, the reduced form of Mtb DsbE is more stable than the oxidized form, and Mtb DsbE is able to oxidatively fold hirudin. Structural and biochemical analysis implies that Mtb DsbE functions differently from Gram-negative DsbE homologs, and we discuss its possible functional role in the bacterium.
Subject(s)
Antigens, Bacterial/chemistry , Antigens, Bacterial/physiology , Bacterial Proteins/chemistry , Bacterial Proteins/physiology , Gram-Negative Bacteria/metabolism , Gram-Positive Bacteria/metabolism , Amino Acid Sequence , Binding Sites , Catalysis , Crystallography, X-Ray , Cysteine/chemistry , Cytoplasm/metabolism , Databases, Genetic , Dimerization , Disulfides/chemistry , Dose-Response Relationship, Drug , Escherichia coli/metabolism , Hirudins/chemistry , Hydrogen-Ion Concentration , Kinetics , Models, Biological , Models, Molecular , Molecular Sequence Data , Mycobacterium tuberculosis/metabolism , Oxidation-Reduction , Oxidoreductases/chemistry , Oxygen/metabolism , Plasmids/metabolism , Protein Conformation , Protein Folding , Protein Structure, Secondary , Protein Structure, Tertiary , Sequence Homology, Amino Acid , Structure-Activity Relationship , Sulfhydryl Compounds , Thermodynamics , X-Ray DiffractionABSTRACT
Tuberculosis (TB) in cattle remains a major zoonotic and economic problem in many countries. Since the standard diagnostic assay, the intradermal test (IDT) with bovine PPD tuberculin, has less than optimal accuracy in all situations, other diagnostic methods such as serological assays have been investigated. Because of fundamental concerns for the low sensitivity and specificity of previous ELISA protocols, a profiling ELISA with nine purified, recombinant proteins of TB complex mycobacteria, was employed on samples from four groups of cattle: (a) naturally Mycobacterium avium-exposed and experimentally Mycobacterium bovis-infected, (b) officially-certified TB-free herds, (c) exposed to M. bovis in two field TB outbreaks and scored as bovine reactors in the gamma-IFN assay for bovine TB, (d) paratuberculosis (para TB)-infected. The described ELISA proved to be highly specific. In fact, the antibody (Ab) response could be consistently detected in 3 out of 3 endotracheally-infected calves and in 1 out of 3 contact-infected calves. There was also a very low prevalence of low-titered, non-specific Ab responses in paraTB-infected animals. As for the animals exposed to field TB outbreaks, 16 out of 28 gamma-IFN positive cattle were also Ab-positive; importantly, 7 out of 12 gamma-IFN positive, IDT-negative cattle showed Ab responses to TB proteins. In general, the profile of the Ab response varied among animals; the reaction to single recombinant antigens was sometimes transient and fluctuating, whereas the panel of antigens on the whole was indeed more effective in Ab detection.
