Cross-regulation of antibody responses against the SARS-CoV-2 Spike protein and commensal microbiota via molecular mimicry

The commensal microflora provides a repertoire of antigens that illicit mucosal antibodies. In some cases, these antibodies can cross-react with host proteins, inducing autoimmunity, or with other microbial antigens. We demonstrate that the oral microbiota can induce salivary anti-SARS-CoV-2 Spike IgG antibodies via molecular mimicry. Anti-Spike IgG antibodies in the saliva correlated with enhanced abundance of Streptococcus salivarius 1 month after anti-SARS-CoV-2 vaccination. Several human commensal bacteria, including S. salivarius, were recognized by SARS-CoV-2-neutralizing monoclonal antibodies and induced cross-reactive anti-Spike antibodies in mice, facilitating SARS-CoV-2 clearance. A specific S. salivarius protein, RSSL-01370, contains regions with homology to the Spike receptor-binding domain, and immunization of mice with RSSL-01370 elicited anti-Spike IgG antibodies in the serum. Additionally, oral S. salivarius supplementation enhanced salivary anti-Spike antibodies in vaccinated individuals. Altogether, these data show that distinct species of the human microbiota can express molecular mimics of SARS-CoV-2 Spike protein, potentially enhancing protective immunity.

TNF hampers intestinal tissue repair in colitis by restricting IL-22 bioavailability

Successful treatment of chronic inflammatory diseases integrates both the cessation of inflammation and the induction of adequate tissue repair processes. Strikingly, targeting a single proinflammatory cytokine, tumor necrosis factor (TNF), induces both processes in a relevant cohort of inflammatory bowel disease (IBD) patients. However, the molecular mechanisms underlying intestinal repair following TNF blockade during IBD remain elusive. Using a novel humanized model of experimental colitis, we demonstrate that TNF interfered with the tissue repair program via induction of a soluble natural antagonist of IL-22 (IL-22Ra2; IL-22BP) in the colon and abrogated IL-22/STAT3-mediated mucosal repair during colitis. Furthermore, membrane-bound TNF expressed by T cells perpetuated colonic inflammation, while soluble TNF produced by epithelial cells (IECs) induced IL-22BP expression in colonic dendritic cells (DCs) and dampened IL-22-driven restitution of colonic epithelial functions. Finally, TNF induced IL-22BP expression in human monocyte-derived DCs and levels of IL22-BP correlated with TNF in sera of IBD patients. Thus, our data can explain how anti-TNF therapy induces mucosal healing by increasing IL-22 availability and implicates new therapeutic opportunities for IBD.

SARS-CoV-2 in severe COVID-19 induces a TGF-β-dominated chronic immune response that does not target itself

The pathogenesis of severe COVID-19 reflects an inefficient immune reaction to SARS-CoV-2. Here we analyze, at the single cell level, plasmablasts egressed into the blood to study the dynamics of adaptive immune response in COVID-19 patients requiring intensive care. Before seroconversion in response to SARS-CoV-2 spike protein, peripheral plasmablasts display a type 1 interferon-induced gene expression signature; however, following seroconversion, plasmablasts lose this signature, express instead gene signatures induced by IL-21 and TGF-β, and produce mostly IgG1 and IgA1. In the sustained immune reaction from COVID-19 patients, plasmablasts shift to the expression of IgA2, thereby reflecting an instruction by TGF-β. Despite their continued presence in the blood, plasmablasts are not found in the lungs of deceased COVID-19 patients, nor does patient IgA2 binds to the dominant antigens of SARS-CoV-2. Our results thus suggest that, in severe COVID-19, SARS-CoV-2 triggers a chronic immune reaction that is instructed by TGF-β, and is distracted from itself.

Interplay Between Microbiota, Toll-Like Receptors and Cytokines for the Maintenance of Epithelial Barrier Integrity

The intestinal tract is densely populated by microbiota consisting of various commensal microorganisms that are instrumental for the healthy state of the living organism. Such commensals generate various molecules that can be recognized by the Toll-like receptors of the immune system leading to the inflammation marked by strong upregulation of various proinflammatory cytokines, such as TNF, IL-6, and IL-1β. To prevent excessive inflammation, a single layer of constantly renewing, highly proliferating epithelial cells (IEC) provides proper segregation of such microorganisms from the body cavities. There are various triggers which facilitate the disturbance of the epithelial barrier which often leads to inflammation. However, the nature and duration of the stress may determine the state of the epithelial cells and their responses to cytokines. Here we discuss the role of the microbiota-TLR-cytokine axis in the maintenance of the epithelial tissue integrity. In particular, we highlight discrepancies in the function of TLR and cytokines in IEC barrier during acute or chronic inflammation and we suggest that intervention strategies should be applied based on the type of inflammation.

Specific microbiota enhances intestinal IgA levels by inducing TGF-β in T follicular helper cells of Peyer's patches in mice

In humans and mice, mucosal immune responses are dominated by IgA antibodies and the cytokine TGF-β, suppressing unwanted immune reactions but also targeting Ig class switching to IgA. It had been suggested that eosinophils promote the generation and maintenance of mucosal IgA-expressing plasma cells. Here, we demonstrate that not eosinophils, but specific bacteria determine mucosal IgA production. Co-housing of eosinophil-deficient mice with mice having high intestinal IgA levels, as well as the intentional microbiota transfer induces TGF-β expression in intestinal T follicular helper cells, thereby promoting IgA class switching in Peyer's patches, enhancing IgA⁺ plasma cell numbers in the small intestinal lamina propria and levels of mucosal IgA. We show that bacteria highly enriched for the genus Anaeroplasma are sufficient to induce these changes and enhance IgA levels when adoptively transferred. Thus, specific members of the intestinal microbiota and not the microbiota as such regulate gut homeostasis, by promoting the expression of immune-regulatory TGF-β and of mucosal IgA.

Antibiotic treatment-induced secondary IgA deficiency enhances susceptibility to Pseudomonas aeruginosa pneumonia

Broad-spectrum antibiotics are widely used with patients in intensive care units (ICUs), many of whom develop hospital-acquired infections with Pseudomonas aeruginosa. Although preceding antimicrobial therapy is known as a major risk factor for P. aeruginosa-induced pneumonia, the underlying mechanisms remain incompletely understood. Here we demonstrate that depletion of the resident microbiota by broad-spectrum antibiotic treatment inhibited TLR-dependent production of a proliferation-inducing ligand (APRIL), resulting in a secondary IgA deficiency in the lung in mice and human ICU patients. Microbiota-dependent local IgA contributed to early antibacterial defense against P. aeruginosa. Consequently, P. aeruginosa-binding IgA purified from lamina propria culture or IgA hybridomas enhanced resistance of antibiotic-treated mice to P. aeruginosa infection after transnasal substitute. Our study provides a mechanistic explanation for the well-documented risk of P. aeruginosa infection following antimicrobial therapy, and we propose local administration of IgA as a novel prophylactic strategy.

[Analysis of the Specificity of IgA Antibodies Produced in the Mouse Small Intestine]

Intestinal microbiota controls multiple aspects of body homeostasis. The microbiota composition changes easily in response to internal or external factors, which may result in dysbiosis and associated inflammatory reactions. Thus, maintaining the microbiota composition by the host immune system is crucial, and one of the main mechanisms for microbiota control is production of immunoglobulin A (IgA) at mucosal surfaces. The molecular mechanisms regulating the interactions between the immune system and microbiota remain obscure. A panel of hybridoma cell lines was constructed to produce monoclonal IgA antibodies specific to various commensal bacteria present in intestinal microbiota. The panel can be used to further understand the mechanisms whereby the adaptive immune system controls the microbiota composition.

Altered polymorphonuclear neutrophilic granulocyte functions in patients with large burns

Multiparameter flow cytometric analyses of polymorphonuclear neutrophilic granulocyte (PMNL) functions have been performed longitudinally in ten patients with large burns. The percentage of phagocytosing PMNLs was increased at admission (within 24 hours after injury) and through the first 10 days of hospitalization. The surface binding capacity and the ingestion of Staphylococcus aureus by each PMNL was increased during the same time period, and at day 2 the number of S. aureus ingested per patient PMNL was 35% higher than in the controls. The intracellular killing of Candida albicans was reduced by about 25% at admission. The microbicidal capacity was further compromised during the first 2 weeks after injury, with a reduction of intracellular killing of about 35% 5-10 days after admission. The kinetics of patient PMNL phagolysosomal acidification was altered during the first 20 days, as the initial alkalinization of the phagolysosomes documented in control PMNLs could not be demonstrated in PMNLs from patients with burns. In addition, measurements of maximal phagolysosomal acidification showed a lower pH in patient phagolysosomes than in the controls during the first 5 days. The patient PMNL H2O2 production was reduced at admission and through the first 10 days, with an oxidative burst that was 46% lower than the controls at day 5. The intracellular degradation of S. aureus proteins and DNA was slightly but significantly reduced at day 5 and day 10 after admission. The impairment of PMNL microbicidal capacity correlated with total body surface area burn.(ABSTRACT TRUNCATED AT 250 WORDS)

Elastase and suppressor active peptide activity following burn injury

Proteolytic enzyme activity following trauma and inflammation plays a key role in the pathophysiology of injury. The precise mechanisms involved in the induction of protease release has not been determined. We show here that sera from burn patients with greater than 40% TBSA have significantly elevated levels of active elastase which correspond with significantly increased levels of suppressor active peptide (SAP) and suppression of neutrophil chemotaxis. The elastase inhibitory capacity of serum from burned or blunt trauma patients was within normal range, suggesting that the primary elastase inhibitor, alpha-1-proteinase inhibitor, is functionally active. Additionally, granulocytes exposed to suppressor active peptide in vitro resulted in a markedly elevated release of elastase into the culture supernatants. These data suggest that the suppressor peptide is capable of not only suppressing immune function but is also a potent mediator for the induction of proteolytic enzyme release from leukocytes.

The effect of exchange therapy on postburn lymphocyte suppression

Circulating mediators have been implicated in the pathophysiology of postburn immunologic depression, suggesting the restorative potential of exchange therapy. Previous reports have stressed the immunosuppressive effects of massive transfusions and major surgical procedures. The effect of plasma exchange (PLA/EX) and surgical excision and grafting (E/G) procedures on postburn lymphocyte function was evaluated retrospectively in one-way mixed lymphocyte reaction assays. Twenty one adult patients with a mean total body surface area (TBSA) burn of 52.6% underwent a total of 54 PLA/EX procedures without complications. The mean volume of plasma exchanged was 5079 ml. PLA/EX was performed at a mean time of 10.4 days after burn injury. Thirty adult patients with a mean TBSA burn of 42.8% underwent a total of 78 E/G procedures. The mean graft size was 2373 cm2 per E/G procedure or 7.25% TBSA. The mean transfusion requirement per E/G was 3355 ml. The initial E/G occurred at a mean of 7.5 days after burn injury. PLA/EX decreased suppression of normal lymphocyte blastogenesis by burn serum from 62.7% to 28.3% (p less than 0.001). The mean duration of improvement in lymphocyte function was 4.8 days. Similarly, the mean suppression by burn serum drawn pre-E/G was 42.2%, while serum suppressive activity post-E/G was 29.1% (p less than 0.05). The mean duration of mixed lymphocyte reaction improvement was 5.0 days. Both PLA/EX and E/G procedures have a significant beneficial effect in restoring lymphocyte function in burn patients.

Viability of frozen allografts

The use of meshed skin grafts allows an evaluation of the biologic properties of stored tissues such as skin. Frozen allograft may serve as an excellent biologic membrane, but it is not a satisfactory product for longer term allografting (intermediate allografting). The method of thawing (microwave oven versus water bath) appeared to have little effect on the ultimate viability and outcome of the frozen allograft.