Pulmonary immunity to viruses

B cells secrete functional antigen-specific IgG antibodies on extracellular vesicles

B cells and the antibodies they produce are critical in host defense against pathogens and contribute to various immune-mediated diseases. B cells responding to activating signals in vitro release extracellular vesicles (EV) that carry surface antibodies, yet B cell production of EVs that express antibodies and their function in vivo is incompletely understood. Using transgenic mice expressing the Cre recombinase in B cells switching to IgG1 to induce expression of fusion proteins between emerald green fluorescent protein (emGFP) and the EV tetraspanin CD63 as a model, we identify emGFP expression in B cells responding to foreign antigen in vivo and characterize the emGFP+ EVs they release. Our data suggests that emGFP+ germinal center B cells undergoing immunoglobulin class switching to express IgG and their progeny memory B cells and plasma cells, also emGFP+, are sources of circulating antigen-specific IgG+ EVs. Furthermore, using a mouse model of influenza virus infection, we find that IgG+ EVs specific for the influenza hemagglutinin antigen protect against virus infection. In addition, crossing the B cell Cre driver EV reporter mice onto the Nba2 lupus-prone strain revealed increased circulating emGFP+ EVs that expressed surface IgG against nuclear antigens linked to autoimmunity. These data identify EVs loaded with antibodies as a novel route for antibody secretion in B cells that contribute to adaptive immune responses, with important implications for different functions of IgG+ EVs in infection and autoimmunity.

Regulation of pulmonary plasma cell responses during secondary infection with influenza virus

During secondary infection with influenza virus, plasma cells (PCs) develop within the lung, providing a local source of antibodies. However, the site and mechanisms that regulate this process are poorly defined. Here, we show that while circulating memory B cells entered the lung during rechallenge and were activated within inducible bronchus-associated lymphoid tissues (iBALTs), resident memory B (BRM) cells responded earlier, and their activation occurred in a different niche: directly near infected alveoli. This process required NK cells but was largely independent of CD4 and CD8 T cells. Innate stimuli induced by virus-like particles containing ssRNA triggered BRM cell differentiation in the absence of cognate antigen, suggesting a low threshold of activation. In contrast, expansion of PCs in iBALTs took longer to develop and was critically dependent on CD4 T cells. Our work demonstrates that spatially distinct mechanisms evolved to support pulmonary secondary PC responses, and it reveals a specialized function for BRM cells as guardians of the alveoli.

Intraperitoneal versus intranasal administration of lipopolysaccharide in causing sepsis severity in a murine model: a preliminary comparison

Community-acquired respiratory infection is the commonest cause of sepsis presenting to emergency departments. Yet current experimental animal models simulate peritoneal sepsis with intraperitoneal (I.P.) injection of lipopolysaccharide (LPS) as the predominant route. We aimed to compare the progression of organ injury between I.P. LPS and intranasal (I.N.) LPS in order to establish a better endotoxemia murine model of respiratory sepsis. Eight weeks old male BALB/c mice received LPS-Escherichia coli doses at 0.15, 1, 10, 20, 40 and 100 mg per kg body weight (e.g. LPS-10 is a dose of 10 mg/kg body weight). Disease severity was monitored by a modified Mouse Clinical Assessment Score for Sepsis (M-CASS; range 0-21). A M-CASS score ≥ 10 or a weight reduction of ≥ 20%, was used as a criterion for euthanasia. The primary outcome was the survival rate (either no death or no need for euthanasia). The progression of disease was specified as M-CASS, body weight, blood glucose, histopathological changes to lung, liver, spleen, kidney, brain and heart tissues. Survival rate in I.P. LPS-20 mice was 0% (2/3 died; 1/3 euthanized with M-CASS > 10) at 24 h. Survival rate in all doses of I.N. LPS was 100% (20/20; 3-4 per group) at 96 h. 24 h mean M-CASS post-I.P. LPS-10 was 6.4/21 significantly higher than I.N. LPS-10 of 1.7/21 (Unpaired t test, P < 0.05). Organ injury was present at 96 h in the I.P. LPS-10 group: lung (3/3; 100%), spleen (3/3; 100%) and liver (1/3; 33%). At 24 h in the I.P. LPS-20 group, kidney injury was observed in the euthanized mouse. At 96 h in the post-I.N. LPS-20 group, only lung injury was observed in 2/3 (67%) mice (Kruskal-Wallis test with Dunn's, P < 0.01). At 24 h in the post-I.N. LPS-100 group all (4/4) mice had evidence of lung injury. Variable doses of I.N. LPS in mice produced lung injury but did not produce sepsis. Higher doses of I.P. LPS induced multi-organ injury but not respiratory sepsis. Lethal models of respiratory virus, e.g., influenza A, might provide alternative avenues that can be explored in future research.

Advances in immune response to pulmonary infection: Nonspecificity, specificity and memory

The lung immune response consists of various cells involved in both innate and adaptive immune processes. Innate immunity participates in immune resistance in a nonspecific manner, whereas adaptive immunity effectively eliminates pathogens through specific recognition. It was previously believed that adaptive immune memory plays a leading role during secondary infections; however, innate immunity is also involved in immune memory. Trained immunity refers to the long-term functional reprogramming of innate immune cells caused by the first infection, which alters the immune response during the second challenge. Tissue resilience limits the tissue damage caused by infection by controlling excessive inflammation and promoting tissue repair. In this review, we summarize the impact of host immunity on the pathophysiological processes of pulmonary infections and discuss the latest progress in this regard. In addition to the factors influencing pathogenic microorganisms, we emphasize the importance of the host response.

Blood heparin-binding protein and neutrophil-to-lymphocyte ratio as indicators of the severity and prognosis of community-acquired pneumonia

BACKGROUND

Community-acquired pneumonia (CAP) is particularly prevalent and has high mortality in severely ill patients, but the role of current biomarkers is limited. This study aimed to evaluate the importance of blood heparin-binding protein (HBP) and neutrophil-to-lymphocyte ratio (NLR) in assessing the severity and prognosis of CAP in adults.

METHODS

The clinical information of 206 CAP patients was retrospectively analyzed. Receiver operating characteristic (ROC) curves were created, and the accuracy of the diagnosis of severe pneumonia was evaluated by the area under the curve (AUC). Univariate and multivariate Cox regression analysis was used to examine independent factors affecting the 30-day prognosis. The Kruskal-Wallis test was utilized to contrast the variations among etiology.

RESULTS

Patients with severe pneumonia showed greater HBP and NLR compared to those with common pneumonia. The AUC of HBP was 0.723 (95% CI: 0.655-0.790) for the diagnosis of severe pneumonia, while NLR and HBP exhibited superior sensitivity (80.00%) and specificity (76.19%), respectively. Their combination boosted the diagnostic specificity (84.13%) while increasing the diagnostic sensitivity (86.25%) when combined with white blood cell (WBC) count. The 30-day mortality in CAP patients was independently predicted by HBP and NLR. However, there were no appreciable differences in HBP amongst patients with various etiologies.

CONCLUSION

HBP and NLR were also independent predictors of 30-day death in CAP patients and grew with increasing severity in these patients. Their combination opened up new possibilities. Furthermore, there is no connection between HBP and the etiology of CAP.

Rethinking next-generation vaccines for coronaviruses, influenzaviruses, and other respiratory viruses

Viruses that replicate in the human respiratory mucosa without infecting systemically, including influenza A, SARS-CoV-2, endemic coronaviruses, RSV, and many other "common cold" viruses, cause significant mortality and morbidity and are important public health concerns. Because these viruses generally do not elicit complete and durable protective immunity by themselves, they have not to date been effectively controlled by licensed or experimental vaccines. In this review, we examine challenges that have impeded development of effective mucosal respiratory vaccines, emphasizing that all of these viruses replicate extremely rapidly in the surface epithelium and are quickly transmitted to other hosts, within a narrow window of time before adaptive immune responses are fully marshaled. We discuss possible approaches to developing next-generation vaccines against these viruses, in consideration of several variables such as vaccine antigen configuration, dose and adjuventation, route and timing of vaccination, vaccine boosting, adjunctive therapies, and options for public health vaccination polices.

Integrating network pharmacology and experimental verification to decipher the immunomodulatory effect of Bu-Zhong-Yi-Qi-Tang against poly (I:C)-induced pulmonary inflammation

Pulmonary inflammation caused by respiratory tract viral infections is usually associated with acute exacerbation of respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD). Therefore, maintaining the pulmonary immune homeostasis is particular important for prevention of the acute exacerbation. Bu-Zhong-Yi-Qi-Tang (BZYQT), a traditional Chinese medicine formula, has been broadly used to improve respiratory and gastrointestinal disorders in China for over 700 years. Previously, we have found the regulatory activity of BZYQT on the lower respiratory immune system, while its potential effects during pulmonary inflammation remain unknown. Thus, the current study focused on deciphering its immunomodulatory effect and potential mechanism against pulmonary inflammation by using a viral RNA analogue, poly (I:C), induced murine pulmonary inflammation model and BEAS-2B cell model coupled with network pharmacology. Inflammatory cells in the bronchoalveolar lavage fluid were counted through microscope examination according to the cell’s morphology and staining characteristics; protein and gene levels of inflammatory mediators were determined with Elisa and quantitative PCR, respectively; network pharmacology was conducted based on 46 BZYQT-related potential bioactive components, pulmonary inflammation and immune-related targets. Our results indicated that the recruitment of neutrophils and the expression of Adgre1 (encoding the F4/80, which is a macrophage marker) in the lung induced by poly (I:C) were significantly reduced after BZYQT treatment, and these effects were further demonstrated to be related to the interference of leukocyte transendothelial migration from the decreased levels of CXCL10, IL-6, TNF-α, CXCL2, ICAM-1, VCAM-1, and E/P-selectins. Furthermore, BZYQT inhibited the CXCL10, TNF-α, and IFN-β expression of poly (I:C)-challenged BEAS-2B cells in a dose-dependent manner. Through integrating results from network pharmacology, experiments, and the published literature, isoliquiritigenin, Z-ligustilide, atractylenolide I, atractylenolide III, formononetin, ferulic acid, hesperidin, and cimigenoside were presumed as the bioactive components of BZYQT against pulmonary inflammation. Overall, our findings demonstrated that BZYQT possesses a pronounced immunomodulatory effect on poly (I:C)-induced pulmonary inflammation, which provides a pharmacological basis for BZYQT in the treatment of respiratory disorders.

Zinc and Respiratory Viral Infections: Important Trace Element in Anti-viral Response and Immune Regulation

Influenza viruses, respiratory syncytial virus (RSV), and SARS-COV2 are among the most dangerous respiratory viruses. Zinc is one of the essential micronutrients and is very important in the immune system. The aim of this narrative review is to review the most interesting findings about the importance of zinc in the anti-viral immune response in the respiratory tract and defense against influenza, RSV, and SARS-COV2 infections. The most interesting findings on the role of zinc in regulating immunity in the respiratory tract and the relationship between zinc and acute respiratory distress syndrome (ARDS) are reviewed, as well. Besides, current findings regarding the relationship between zinc and the effectiveness of respiratory viruses' vaccines are reviewed. The results of reviewed studies have shown that zinc and some zinc-dependent proteins are involved in anti-viral defense and immune regulation in the respiratory tract. It seems that zinc can reduce the viral titer following influenza infection. Zinc may reduce RSV burden in the lungs. Zinc can be effective in reducing the duration of viral pneumonia symptoms. Zinc may enhance the effectiveness of hydroxychloroquine in reducing mortality rate in COVID-19 patients. Besides, zinc has a positive effect in preventing ARDS and ventilator-induced lung damage. The relationship between zinc levels and the effectiveness of respiratory viruses' vaccines, especially influenza vaccines, is still unclear, and the findings are somewhat contradictory. In conclusion, zinc has anti-viral properties and is important in defending against respiratory viral infections and regulating the immune response in the respiratory tract.

Strong influenza-induced TFH generation requires CD4 effectors to recognize antigen locally and receive signals from continuing infection

Influenza infection elicits strong, long-lived protective antibodies, but most current influenza vaccines give weaker, short-lived protection. We noted that live virus is still replicating, making antigen and causing inflammation at 7 d postinfection (dpi), while an inactivated vaccine provides antigen for at most 4 dpi. We show that the generation of key T follicular helper cells (T_FH) requires they recognize antigen locally at 6 dpi in the presence of ongoing viral infection. This creates a checkpoint that restricts T_FH responses to dangerous infections that persist through the checkpoint. Using a live attenuated vaccine, akin to Flumist, we found that adding a second dose at 6 d generated a strong T_FH response, suggesting an approach to improve vaccine strategies.

While influenza infection induces robust, long-lasting, antibody responses and protection, including the T follicular helper cells (T_FH) required to drive B cell germinal center (GC) responses, most influenza vaccines do not. We investigated the mechanisms that drive strong T_FH responses during infection. Infection induces viral replication and antigen (Ag) presentation lasting through the CD4 effector phase, but Ag and pathogen recognition receptor signals are short-lived after vaccination. We analyzed the need for both infection and Ag presentation at the effector phase, using an in vivo sequential transfer model to time their availability. Differentiation of CD4 effectors into T_FH and GC-T_FH required that they recognize Ag locally in the site of T_FH development, at the effector phase, but did not depend on specific Ag-presenting cells (APCs). In addition, concurrent signals from infection were necessary even when sufficient Ag was presented. Providing these signals with a second dose of live attenuated influenza vaccine at the effector phase drove T_FH and GC-T_FH development equivalent to live infection. The results suggest that vaccine approaches can induce strong T_FH development that supports GC responses akin to infection, if they supply these effector phase signals at the right time and site. We suggest that these requirements create a checkpoint that ensures T_FH only develop fully when infection is still ongoing, thereby avoiding unnecessary, potentially autoimmune, responses.

Nanotechnologies in Delivery of DNA and mRNA Vaccines to the Nasal and Pulmonary Mucosa

Recent advancements in the field of in vitro transcribed mRNA (IVT-mRNA) vaccination have attracted considerable attention to such vaccination as a cutting-edge technique against infectious diseases including COVID-19 caused by SARS-CoV-2. While numerous pathogens infect the host through the respiratory mucosa, conventional parenterally administered vaccines are unable to induce protective immunity at mucosal surfaces. Mucosal immunization enables the induction of both mucosal and systemic immunity, efficiently removing pathogens from the mucosa before an infection occurs. Although respiratory mucosal vaccination is highly appealing, successful nasal or pulmonary delivery of nucleic acid-based vaccines is challenging because of several physical and biological barriers at the airway mucosal site, such as a variety of protective enzymes and mucociliary clearance, which remove exogenously inhaled substances. Hence, advanced nanotechnologies enabling delivery of DNA and IVT-mRNA to the nasal and pulmonary mucosa are urgently needed. Ideal nanocarriers for nucleic acid vaccines should be able to efficiently load and protect genetic payloads, overcome physical and biological barriers at the airway mucosal site, facilitate transfection in targeted epithelial or antigen-presenting cells, and incorporate adjuvants. In this review, we discuss recent developments in nucleic acid delivery systems that target airway mucosa for vaccination purposes.

Co-Ordination of Mucosal B Cell and CD8 T Cell Memory by Tissue-Resident CD4 Helper T Cells

Adaptive cellular immunity plays a major role in clearing microbial invasion of mucosal tissues in mammals. Following the clearance of primary pathogens, memory lymphocytes are established both systemically and locally at pathogen entry sites. Recently, resident memory CD8 T and B cells (T_RM and B_RM respectively), which are parked mainly in non-lymphoid mucosal tissues, were characterized and demonstrated to be essential for protection against secondary microbial invasion. Here we reviewed the current understanding of the cellular and molecular cues regulating CD8 T_RM and B_RM development, maintenance and function. We focused particularly on elucidating the role of a novel tissue-resident helper T (T_RH) cell population in assisting T_RM and B_RM responses in the respiratory mucosa following viral infection. Finally, we argue that the promotion of T_RH responses by future mucosal vaccines would be key to the development of successful universal influenza or coronavirus vaccines, providing long-lasting immunity against a broad spectrum of viral strains.

FcRn-Targeted Mucosal Vaccination against Influenza Virus Infection

The respiratory tract is constantly exposed to various airborne pathogens. Most vaccines against respiratory infections are designed for the parenteral routes of administration; consequently, they provide relatively minimal protection in the respiratory tract. A vaccination strategy that aims to induce the protective mucosal immune responses in the airway is urgently needed. The FcRn mediates IgG Ab transport across the epithelial cells lining the respiratory tract. By mimicking this natural IgG transfer, we tested whether FcRn delivers vaccine Ags to induce a protective immunity to respiratory infections. In this study, we designed a monomeric IgG Fc fused to influenza virus hemagglutinin (HA) Ag with a trimerization domain. The soluble trimeric HA-Fc were characterized by their binding with conformation-dependent HA Abs or FcRn. In wild-type, but not FcRn knockout, mice, intranasal immunization with HA-Fc plus CpG adjuvant conferred significant protection against lethal intranasal challenge with influenza A/PR/8/34 virus. Further, mice immunized with a mutant HA-Fc lacking FcRn binding sites or HA alone succumbed to lethal infection. Protection was attributed to high levels of neutralizing Abs, robust and long-lasting B and T cell responses, the presence of lung-resident memory T cells and bone marrow plasma cells, and a remarkable reduction of virus-induced lung inflammation. Our results demonstrate for the first time, to our knowledge, that FcRn can effectively deliver a trimeric viral vaccine Ag in the respiratory tract and elicit potent protection against respiratory infection. This study further supports a view that FcRn-mediated mucosal immunization is a platform for vaccine delivery against common respiratory pathogens.

Immunity to Influenza Infection in Humans

This review discusses the human immune responses to influenza infection with some insights from studies using animal models, such as experimental infection of mice. Recent technological advances in the study of human immune responses have greatly added to our knowledge of the infection and immune responses, and therefore much of the focus is on recent studies that have moved the field forward. We consider the complexity of the adaptive response generated by many sequential encounters through infection and vaccination.

Tissue-resident CD4+ T helper cells assist the development of protective respiratory B and CD8+ T cell memory responses

Much remains unknown about the roles of CD4⁺ T helper cells in shaping localized memory B cell and CD8⁺ T cell immunity in the mucosal tissues. Here, we report that lung T helper cells provide local assistance for the optimal development of tissue-resident memory B and CD8⁺ T cells after the resolution of primary influenza virus infection. We have identified a population of T cells in the lung that exhibit characteristics of both follicular T helper and T_RM cells, and we have termed these cells as resident helper T (T_RH) cells. Optimal T_RH cell formation was dependent on transcription factors involved in T follicular helper and resident memory T cell development including BCL6 and Bhlhe40. We show that T_RH cells deliver local help to CD8⁺ T cells through IL-21-dependent mechanisms. Our data have uncovered the presence of a tissue-resident helper T cell population in the lung that plays a critical role in promoting the development of protective B cell and CD8⁺ T cell responses.

Current Insights into the Host Immune Response to Respiratory Viral Infections

Respiratory viral infections often lead to severe illnesses varying from mild or asymptomatic upper respiratory tract infections to severe bronchiolitis and pneumonia or/and chronic obstructive pulmonary disease. Common viral infections, including but not limited to influenza virus, respiratory syncytial virus, rhinovirus and coronavirus, are often the leading cause of morbidity and mortality. Since the lungs are continuously exposed to foreign particles, including respiratory pathogens, it is also well equipped for recognition and antiviral defense utilizing the complex network of innate and adaptive immune cells. Immediately upon infection, a range of proinflammatory cytokines, chemokines and an interferon response is generated, thereby making the immune response a two edged sword, on one hand it is required to eliminate viral pathogens while on other hand it's prolonged response can lead to chronic infection and significant pulmonary damage. Since vaccines to all respiratory viruses are not available, a better understanding of the virus-host interactions, leading to the development of immune response, is critically needed to design effective therapies to limit the severity of inflammatory damage, enhance viral clearance and to compliment the current strategies targeting the virus. In this chapter, we discuss the host responses to common respiratory viral infections, the key players of adaptive and innate immunity and the fine balance that exists between the viral clearance and immune-mediated damage.

The Interplay Between Respiratory Microbiota and Innate Immunity in Flavor E-Cigarette Vaping Induced Lung Dysfunction

Global usage of electronic nicotine delivery systems (ENDS) has been increasing in the last decade. ENDS are non-combustible tobacco products that heat and aerosolize a liquid containing humectants, with added flavorings and often nicotine. Though ENDS are promoted as a less harmful alternative to smoking, current evidence links their use to a wide range of deleterious health effects including acute and chronic lung damage. ENDS can elicit an inflammatory response and impair the innate immune response in the lungs. Exposure to ENDS flavorings results in abnormal activation of the lung epithelial cells and β-defensins, dysfunction of the macrophage phagocytic activity, increased levels of mucin (MUC5AC) and abnormal activation of the neutrophilic response (NETosis). ENDS menthol flavorings disrupt innate immunity and might be associated with allergies and asthma through activation of transient receptor potential ankyrin 1 (TRAP1). Recent studies have expanded our understanding of the relationship between the homeostasis of lung innate immunity and the immunomodulatory effect of the host-microbiota interaction. Alterations of the normal respiratory microbiota have been associated with chronic obstructive pulmonary disease (COPD), asthma, atopy and cystic fibrosis complications which are strongly associated with smoking and potentially with ENDS use. Little is known about the short-and long-term effects of ENDS on the respiratory microbiota, their impact on the innate immune response and their link to pulmonary health and disease. Here we review the interaction between the innate immune system and the respiratory microbiota in the pathogenesis of ENDS-induced pulmonary dysfunction and identify future areas of research.

Evaluating ELISA, Immunofluorescence, and Lateral Flow Assay for SARS-CoV-2 Serologic Assays

Background

The SARS-CoV-2 outbreak has emerged at the end of 2019. Aside from the detection of viral genome with specific RT-PCR, there is a growing need for reliable determination of the serological status. We aimed at evaluating five SARS-CoV-2 serology assays.

Methods

An in-house immunofluorescence assay (IFA), two ELISA kits (EUROIMMUN^® ELISA SARS-CoV-2 IgG and NovaLisa^® SARS-CoV-2 IgG and IgM) and two lateral flow assays (T-Tek^® SARS-CoV-2 IgG/IgM Antibody Test Kit and Sure Bio-tech^® SARS-CoV-2 IgM/IgG Antibody Rapid Test) were compared on 40 serums from RT-PCR-confirmed SARS-CoV-2 infected patients and 10 SARS-CoV-2 RT-PCR negative subjects as controls.

Results

Control subjects tested negative for SARS-CoV-2 antibodies with all five systems. Estimated sensitivities varied from 35.5 to 71.0% for IgG detection and from 19.4 to 64.5% for IgM detection. For IgG, in-house IFA, EuroImmun, T-Tek and NovaLisa displayed 50–72.5% agreement with other systems except IFA vs EuroImmun and T-Tek vs NovaLisa. Intermethod agreement for IgM determination was between 30 and 72.5%.

Discussion

The overall intermethod agreement was moderate. This inconsistency could be explained by the diversity of assay methods, antigens used and immunoglobulin isotype tested. Estimated sensitivities were low, highlighting the limited value of antibody detection in CoVID-19.

Conclusion

Comparison of five systems for SARS-CoV-2 IgG and IgM antibodies showed limited sensitivity and overall concordance. The place and indications of serological status assessment with currently available tools in the CoVID-19 pandemic need further evaluations.

Systemic innate and adaptive immune responses to SARS-CoV-2 as it relates to other coronaviruses

The deadly pandemic caused by the novel coronavirus, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) represents one of the greatest threats humanity has faced in the last century. Infection with this easily transmissible virus can run the gamut from asymptomatic to fatal, and the disease caused by SARS-CoV-2 has been termed Coronavirus Disease 2019 (COVID-19). What little research that has already been conducted implicates pathological responses by the immune system as the leading culprit responsible for much of the morbidity and mortality caused by COVID-19. In this review we will summarize what is currently known about the systemic immune response to SARS-CoV-2 and potential immunotherapeutic approaches.

Mucosal immunity and tRNA, tRF, and tiRNA

Mucosal immunity has crucial roles in human diseases such as respiratory tract infection, inflammatory bowel diseases (IBD), and colorectal cancer (CRC). Recent studies suggest that the mononuclear phagocyte system, cancer cells, bacteria, and viruses induce the mucosal immune reaction by various pathways, and can be major factors in the pathogenesis of these diseases. Transfer RNA (tRNA) and its fragments, including tRNA-derived RNA fragments (tRFs) and tRNA-derived stress-induced RNAs (tiRNAs), have emerged as a hot topic in recent years. They not only are verified as essential for transcription and translation but also play roles in cellular homeostasis and functions, such as cell metastasis, proliferation, and apoptosis. However, the specific relationship between their biological regulation and mucosal immunity remains unclear to date. In the present review, we carry out a comprehensive discussion on the specific roles of tRNA, tRFs, and tiRNAs relevant to mucosal immunity and related diseases.

Integrative transcriptome and chromatin landscape analysis reveals distinct epigenetic regulations in human memory B cells

Memory B cells (MBCs) are long-lived and produce high-affinity, generally, class-switched antibodies. Here, we use a multiparameter approach involving CD27 to segregate naïve B cells (NBC), IgD⁺ unswitched (unsw)MBCs and IgG⁺ or IgA⁺ class-switched (sw)MBCs from humans of different age, sex and race. Conserved antibody variable gene expression indicates that MBCs emerge through unbiased selection from NBCs. Integrative analyses of mRNAs, miRNAs, lncRNAs, chromatin accessibility and cis-regulatory elements uncover a core mRNA-ncRNA transcriptional signature shared by IgG⁺ and IgA⁺ swMBCs and distinct from NBCs, while unswMBCs display a transitional transcriptome. Some swMBC transcriptional signature loci are accessible but not expressed in NBCs. Profiling miRNAs reveals downregulated MIR181, and concomitantly upregulated MIR181 target genes such as RASSF6, TOX, TRERF1, TRPV3 and RORα, in swMBCs. Finally, lncRNAs differentially expressed in swMBCs cluster proximal to the IgH chain locus on chromosome 14. Our findings thus provide new insights into MBC transcriptional programs and epigenetic regulation, opening new investigative avenues on these critical cell elements in human health and disease.

Human memory B cells differentiate from naïve B cells and can express different immunoglobulin (Ig) isotypes resulted from class-switch recombination. Here the authors describe, using transcriptional and epigenetic data from human memory B cells and integrated multi-omics analyses, the differentiation regulation and trajectory of IgG⁺, IgA⁺ and IgD⁺ memory B cells.

Circulating Th1 and Th2 Subset Accumulation Kinetics in Septic Patients with Distinct Infection Sites: Pulmonary versus Nonpulmonary

Background

Persistent peripheral CD4⁺T cell differentiation towards T helper (Th)2 rather than Th1 has been proved to be related to immunosuppression and poor prognosis in sepsis. However, it is unclear whether these circulating Th1 and Th2 subtype accumulations differed in septic populations of distinct infection sites and presented different associations with outcomes among patients with pulmonary versus nonpulmonary sepsis.

Methods

From a secondary analysis of a prospective observational study, seventy-four previously immunocompetent patients with community-acquired severe sepsis within 24 hours upon onset were enrolled. Whole blood was collected on the admission day (D0), 3rd day (D3), and 7th day (D7). The patients were classified as pulmonary (n = 52) and nonpulmonary sepsis (n = 22). Circulating Th1 and Th2 populations were evaluated by flow cytometry, and clinical data related to disease severity and inflammatory response were collected. The associations of circulating Th1 and Th2 subset accumulations with distinct infection sites or outcomes within subgroups were explored.

Results

Patients with pulmonary sepsis held similar disease severity and 28-day mortality with those of nonpulmonary sepsis. Of note is the finding that circulating Th2 levels on D7 (P = 0.04) as well as Th2/Th1 on D3 (P = 0.01) and D7 (P = 0.04) were higher in the pulmonary sepsis compared with nonpulmonary sepsis while Th1 levels were lower on D0, D3, and D7 (P = 0.01, <0.01, and =0.05, respectively). Compared to 28-day survivors, higher Th2/Th1 driven by increased Th2 were observed among 28-day nonsurvivors on D3 and D7 in both groups. The association between circulatory Th2 populations or Th2/Th1 and 28-day death was detected in pulmonary sepsis (P < 0.05, HR > 1), rather than nonpulmonary sepsis.

Conclusions

Circulating Th2 accumulation was more apparent among pulmonary sepsis while nonpulmonary sepsis was characterized with the hyperactive circulating Th1 subset among previously immunocompetent patients. This finding suggested that circulating Th1 and Th2 subset accumulations vary in septic subgroups with different infection sites.

Emerging Role of Mucosal Vaccine in Preventing Infection with Avian Influenza A Viruses

Avian influenza A viruses (AIVs), as a zoonotic agent, dramatically impacts public health and the poultry industry. Although low pathogenic avian influenza virus (LPAIV) incidence and mortality are relatively low, the infected hosts can act as a virus carrier and provide a resource pool for reassortant influenza viruses. At present, vaccination is the most effective way to eradicate AIVs from commercial poultry. The inactivated vaccines can only stimulate humoral immunity, rather than cellular and mucosal immune responses, while failing to effectively inhibit the replication and spread of AIVs in the flock. In recent years, significant progresses have been made in the understanding of the mechanisms underlying the vaccine antigen activities at the mucosal surfaces and the development of safe and efficacious mucosal vaccines that mimic the natural infection route and cut off the AIVs infection route. Here, we discussed the current status and advancement on mucosal immunity, the means of establishing mucosal immunity, and finally a perspective for design of AIVs mucosal vaccines. Hopefully, this review will help to not only understand and predict AIVs infection characteristics in birds but also extrapolate them for distinction or applicability in mammals, including humans.

Mechanisms of Virus-Induced Airway Immunity Dysfunction in the Pathogenesis of COPD Disease, Progression, and Exacerbation

Chronic obstructive pulmonary disease (COPD) is the integrated form of chronic obstructive bronchitis and pulmonary emphysema, characterized by persistent small airway inflammation and progressive irreversible airflow limitation. COPD is characterized by acute pulmonary exacerbations and associated accelerated lung function decline, hospitalization, readmission and an increased risk of mortality, leading to huge social-economic burdens. Recent evidence suggests ~50% of COPD acute exacerbations are connected with a range of respiratory viral infections. Nevertheless, respiratory viral infections have been linked to the severity and frequency of exacerbations and virus-induced secondary bacterial infections often result in a synergistic decline of lung function and longer hospitalization. Here, we review current advances in understanding the cellular and molecular mechanisms underlying the pathogenesis of COPD and the increased susceptibility to virus-induced exacerbations and associated immune dysfunction in patients with COPD. The multiple immune regulators and inflammatory signaling pathways known to be involved in host-virus responses are discussed. As respiratory viruses primarily target airway epithelial cells, virus-induced inflammatory responses in airway epithelium are of particular focus. Targeting virus-induced inflammatory pathways in airway epithelial cells such as Toll like receptors (TLRs), interferons, inflammasomes, or direct blockade of virus entry and replication may represent attractive future therapeutic targets with improved efficacy. Elucidation of the cellular and molecular mechanisms of virus infections in COPD pathogenesis will undoubtedly facilitate the development of these potential novel therapies that may attenuate the relentless progression of this heterogeneous and complex disease and reduce morbidity and mortality.

Resident Memory B Cells

In mammals, adaptive immunity is mediated by a broadly diverse repertoire of naive B and T lymphocytes that recirculate between secondary lymphoid organs. Initial antigen exposure promotes lymphocyte clonal expansion and differentiation, including the formation of memory cells. Antigen-specific memory cells are maintained at higher frequencies than their naive counterparts and have different functional and homing abilities. Importantly, a subset of memory cells, known as tissue-resident memory cells, is maintained without recirculating in nonlymphoid tissues, often at barrier surfaces, where they can be reactivated by antigen and rapidly perform effector functions that help protect the tissue in which they reside. Although antigen-experienced B cells are abundant at many barrier surfaces, their characterization as tissue-resident memory B (BRM) cells is not well developed. In this study, we describe the characteristics of memory B cells in various locations and discuss their possible contributions to immunity and homeostasis as bona fide BRM cells.

Host-Virus Interaction: How Host Cells Defend against Influenza A Virus Infection

Influenza A viruses (IAVs) are highly contagious pathogens infecting human and numerous animals. The viruses cause millions of infection cases and thousands of deaths every year, thus making IAVs a continual threat to global health. Upon IAV infection, host innate immune system is triggered and activated to restrict virus replication and clear pathogens. Subsequently, host adaptive immunity is involved in specific virus clearance. On the other hand, to achieve a successful infection, IAVs also apply multiple strategies to avoid be detected and eliminated by the host immunity. In the current review, we present a general description on recent work regarding different host cells and molecules facilitating antiviral defenses against IAV infection and how IAVs antagonize host immune responses.

CD4 T cells in protection from influenza virus: Viral antigen specificity and functional potential

CD4 T cells convey a number of discrete functions to protective immunity to influenza, a complexity that distinguishes this arm of adaptive immunity from B cells and CD8 T cells. Although the most well recognized function of CD4 T cells is provision of help for antibody production, CD4 T cells are important in many aspects of protective immunity. Our studies have revealed that viral antigen specificity is a key determinant of CD4 T cell function, as illustrated both by mouse models of infection and human vaccine responses, a factor whose importance is due at least in part to events in viral antigen handling. We discuss research that has provided insight into the diverse viral epitope specificity of CD4 T cells elicited after infection, how this primary response is modified as CD4 T cells home to the lung, establish memory, and after challenge with a secondary and distinct influenza virus strain. Our studies in human subjects point out the challenges facing vaccine efforts to facilitate responses to novel and avian strains of influenza, as well as strategies that enhance the ability of CD4 T cells to promote protective antibody responses to both seasonal and potentially pandemic strains of influenza.

ID2 and ID3 are indispensable for Th1 cell differentiation during influenza virus infection in mice

Antigen-specific Th1 cells could be a passage to the infection sites during infection to execute effector functions, such as help CD8⁺ T cells to localize in these sites by secretion of anti-viral cytokines-IFN-γ or direct cytotoxicity of antigen-bearing cells. However, the molecular components that modulate Th1 cell differentiation and function in response to viral infection remain incompletely understood. Here, we reported that both inhibitor of DNA binding 3(Id3) protein and inhibitor of DNA binding 2(Id2) protein promoted Th1 cell differentiation. Depletion of Id3 or Id2 led to severe defect of Th1 cell differentiation during influenza virus infection. Whereas depletion of both Id3 and Id2 in CD4⁺ T cells restrained Th1 cell differentiation to a greater extent, indicating that Id3 and Id2 nonredundantly regulate Th1 cell differentiation. Moreover, deletion of E-proteins, the antagonists of Id proteins, greatly enhanced Th1 cell differentiation. Mechanistic study indicated that E-proteins suppressed Th1 cell differentiation by directly binding to the regulatory elements of Th1 cell master regulator T-bet and regulate T-bet expression. Thus, our findings identified Id-protein's importance for Th1 cells and clarified the nonredundant role of Id3 and Id2 in regulating Th1 cell differentiation, providing novel insight that Id3-Id2-E protein axis are essential for Th1 cell polarization.

Distinct and complementary roles of CD4 T cells in protective immunity to influenza virus

CD4 T cells play a multiplicity of roles in protective immunity to influenza. Included in these functions are help for high affinity antibody production, enhancement of CD8 T cell expansion, function and memory, acceleration of the early innate response to infection and direct cytotoxicity. The influenza-specific CD4 T cell repertoire in humans established through exposures to infection and vaccination has been found to be highly variable in abundance, specificity and functionality. Deficits in particular subsets of CD4 T cells recruited into the response result in diminished antibody responses and protection from infection. Therefore, improved strategies for vaccination should include better methods to identify deficiencies in the circulating CD4 T cell repertoire, and vaccine constructs that increase the representation of CD4 T cells of the correct specificity and functionality.

CD4 T Cell Epitope Specificity and Cytokine Potential Are Preserved as Cells Transition from the Lung Vasculature to Lung Tissue following Influenza Virus Infection

Pulmonary CD4 T cells are critical in respiratory virus control, both by delivering direct effector function and through coordinating responses of other immune cells. Recent studies have shown that following influenza virus infection, virus-specific CD4 T cells are partitioned between pulmonary vasculature and lung tissue. However, very little is known about the peptide specificity or functional differences of CD4 T cells within these two compartments. Using a mouse model of influenza virus infection in conjunction with intravascular labeling in vivo, the cell surface phenotype, epitope specificity, and functional potential of the endogenous polyclonal CD4 T cell response was examined by tracking nine independent CD4 T cell epitope specificities. These studies revealed that tissue-localized CD4 cells were globally distinct from vascular cells in expression of markers associated with transendothelial migration, residency, and micropositioning. Despite these differences, there was little evidence for remodeling of the viral epitope specificity or cytokine potential as cells transition from vasculature to the highly inflamed lung tissue. Our studies also distinguished cells in the pulmonary vasculature from peripheral circulating CD4 T cells, providing support for the concept that the pulmonary vasculature does not simply reflect circulating cells that are trapped within the narrow confines of capillary vessels but rather is enriched in transitional cells primed in the draining lymph node that have specialized potential to enter the lung tissue.IMPORTANCE CD4 T cells convey a multitude of functions in immunity to influenza, including those delivered in the lymph node and others conveyed by CD4 T cells that leave the lymph node, enter the blood, and extravasate into the lung tissue. Here, we show that the transition of recently primed CD4 cells detected in the lung vasculature undergo profound changes in expression of markers associated with tissue localization as they establish residence in the lung. However, this transition does not edit CD4 T cell epitope specificity or the cytokine potential of the CD4 T cells. Thus, CD4 T cells that enter the infected lung can convey diverse functions and have a sufficiently broad viral antigen specificity to detect the complex array of infected cells within the infected tissue, offering the potential for more effective protective function.

Prostaglandin E2 as a Regulator of Immunity to Pathogens

The body is exposed to foreign pathogens every day, but remarkably, most pathogens are effectively cleared by the innate immune system without the need to invoke the adaptive immune response. Key cellular components of the innate immune system include macrophages and neutrophils and the recruitment and function of these cells are tightly regulated by chemokines and cytokines in the tissue space. Innate immune responses are also known to regulate development of adaptive immune responses often via the secretion of various cytokines. In addition to these protein regulators, numerous lipid mediators can also influence innate and adaptive immune functions. In this review, we cover one particular lipid regulator, prostaglandin E2 (PGE2) and describe its synthesis and signaling and what is known about the ability of this lipid to regulate immunity and host defense against viral, fungal and bacterial pathogens.

Diverse Epitope Specificity, Immunodominance Hierarchy, and Functional Avidity of Effector CD4 T Cells Established During Priming Is Maintained in Lung After Influenza A Virus Infection

One of the major contributions to protective immunity to influenza viruses that is provided by virus-specific CD4 T cells is delivery of effector function to the infected lung. However, there is little known about the selection and breadth of viral epitope-specific CD4 T cells that home to the lung after their initial priming. In this study, using a mouse model of influenza A infection and an unbiased method of epitope identification, the viral epitope-specific CD4 T cells elicited after infection were identified and quantified. We found that a very diverse specificity of CD4 T cells is primed by infection, including epitopes from hemagglutinin, neuraminidase, matrix protein, nucleoprotein, and non-structural protein-1. Using peptide-specific cytokine EliSpots, the diversity and immunodominance hierarchies established in the lung-draining lymph node were compared with specificities of CD4 T cells that home to the lung. Our studies revealed that CD4 T cells of all epitope specificities identified in peripheral lymphoid tissue home back to the lung and that most of these lung-homing cells are localized within the tissue rather than the pulmonary vasculature. There is a striking shift of CD4 T cell functionality that enriches for IFN-γ production as cells are primed in the lymph node, enter the lung vasculature, and finally establish residency in the tissue, but with no apparent shifts in their functional avidity. We conclude that CD4 T cells of broad viral epitope specificity are recruited into the lung after influenza infection, where they then have the opportunity to encounter infected or antigen-bearing antigen-presenting cells.

Host Immune Response to Influenza A Virus Infection

Influenza A viruses (IAVs) are contagious pathogens responsible for severe respiratory infection in humans and animals worldwide. Upon detection of IAV infection, host immune system aims to defend against and clear the viral infection. Innate immune system is comprised of physical barriers (mucus and collectins), various phagocytic cells, group of cytokines, interferons (IFNs), and IFN-stimulated genes, which provide first line of defense against IAV infection. The adaptive immunity is mediated by B cells and T cells, characterized with antigen-specific memory cells, capturing and neutralizing the pathogen. The humoral immune response functions through hemagglutinin-specific circulating antibodies to neutralize IAV. In addition, antibodies can bind to the surface of infected cells and induce antibody-dependent cell-mediated cytotoxicity or complement activation. Although there are neutralizing antibodies against the virus, cellular immunity also plays a crucial role in the fight against IAVs. On the other hand, IAVs have developed multiple strategies to escape from host immune surveillance for successful replication. In this review, we discuss how immune system, especially innate immune system and critical molecules are involved in the antiviral defense against IAVs. In addition, we highlight how IAVs antagonize different immune responses to achieve a successful infection.

DUSP1 regulates apoptosis and cell migration, but not the JIP1-protected cytokine response, during Respiratory Syncytial Virus and Sendai Virus infection

The host antiviral response involves the induction of interferons and proinflammatory cytokines, but also the activation of cell death pathways, including apoptosis, to limit viral replication and spreading. This host defense is strictly regulated to eliminate the infection while limiting tissue damage that is associated with virus pathogenesis. Post-translational modifications, most notably phosphorylation, are key regulators of the antiviral defense implying an important role of protein phosphatases. Here, we investigated the role of the dual-specificity phosphatase 1 (DUSP1) in the host defense against human respiratory syncytial virus (RSV), a pathogenic virus of the Pneumoviridae family, and Sendai virus (SeV), a model virus being developed as a vector for anti-RSV vaccine. We found that DUSP1 is upregulated before being subjected to proteasomal degradation. DUSP1 does not inhibit the antiviral response, but negatively regulates virus-induced JNK/p38 MAPK phosphorylation. Interaction with the JNK-interacting protein 1 scaffold protein prevents dephosphorylation of JNK by DUSP1, likely explaining that AP-1 activation and downstream cytokine production are protected from DUSP1 inhibition. Importantly, DUSP1 promotes SeV-induced apoptosis and suppresses cell migration in RSV-infected cells. Collectively, our data unveils a previously unrecognized selective role of DUSP1 in the regulation of tissue damage and repair during infections by RSV and SeV.