A strategy for selective, CD4+ T cell-independent activation of virus-specific memory B cells for limiting dilution analysis

CD4 T cell epitope abundance in ferritin core potentiates responses to hemagglutinin nanoparticle vaccines

Nanoparticle vaccines based on H. pylori ferritin are increasingly used as a vaccine platform for many pathogens, including RSV, influenza, and SARS-CoV-2. They have been found to elicit enhanced, long-lived B cell responses. The basis for improved efficacy of ferritin nanoparticle vaccines remains unresolved, including whether recruitment of CD4 T cells specific for the ferritin component of these vaccines contributes to cognate help in the B cell response. Using influenza HA-ferritin nanoparticles as a prototype, we have performed an unbiased assessment of the CD4 T cell epitope composition of the ferritin particles relative to that contributed by influenza HA using mouse models that express distinct constellations of MHC class II molecules. The role that these CD4 T cells play in the B cell responses was assessed by quantifying follicular helper cells (TFH), germinal center (GC) B cells, and antibody secreting cells. When mice were immunized with equimolar quantities of soluble HA-trimers and HA-Fe nanoparticles, HA-nanoparticle immunized mice had an increased overall abundance of TFH that were found to be largely ferritin-specific. HA-nanoparticle immunized mice had an increased abundance of HA-specific isotype-switched GC B cells and HA-specific antibody secreting cells (ASCs) relative to mice immunized with soluble HA-trimers. Further, there was a strong, positive correlation between CD4 TFH abundance and GC B cell abundance. Thus, availability of helper CD4 T cell epitopes may be a key additional mechanism that underlies the enhanced immunogenicity of ferritin-based HA-Fe-nanoparticle vaccines.

Angiotensin-converting enzyme 2 (ACE2): COVID 19 gate way to multiple organ failure syndromes

BACKGROUND

Globally, the current medical emergency for novel coronavirus 2019 (COVID-19) leads to respiratory distress syndrome and death.

PURPOSE

This review highlighted the effect of COVID-19 on systemic multiple organ failure syndromes. This review is intended to fill a gap in information about human physiological response to COVID-19 infections. This review may shed some light on other potential mechanisms and approaches in COVID -19 infections towards systemic multiorgan failure syndromes.

FINDING

SARS-CoV-2 intervened mainly in the lung with progression to pneumonia and acute respiratory distress syndrome (ARDS) via the angiotensin-converting enzyme 2(ACE2) receptor. Depending on the viral load, infection spread through the ACE2 receptor further to various organs such as heart, liver, kidney, brain, endothelium, GIT, immune cell, and RBC (thromboembolism). This may be aggravated by cytokine storm with the extensive release of proinflammatory cytokines from the deregulating immune system.

CONCLUSION

The widespread and vicious combinations of cytokines with organ crosstalk contribute to systemic hyper inflammation and ultimately lead to multiple organ dysfunction (Fig. 1). This comprehensive study comprises various manifestations of different organs in COVID-19 and may assist the clinicians and scientists pertaining to a broad approach to fight COVID 19.

Adaptive B Cell Responses to Influenza Virus Infection in the Lung

Adaptive B cell response is a key arm of protective immunity against influenza viruses. Owing to the acutely infectious and cytopathic nature of these viruses, efficient containment of viral spread relies on the prompt provision of protective antibodies to the site of virus infection, the respiratory tract (RT). To accelerate the protective antibody response, B cell responses can be ectopically induced, maintained, and reactivated in the lungs after primary and secondary infection, thereby providing an anatomical advantage in supplying neutralizing antibodies against reinfecting viruses with faster kinetics. However, the prompt supply of protective antibodies may be insufficient to protect against reinfection because influenza viruses can easily change their antigenic profiles to escape antibody surveillance. B cell responses have multiple strategies for adjusting antibody repertoires according to viral fitness, one of which is the formation of local germinal centers capable of selecting B cell repertoires for antigenically subdominant, but conserved, epitopes. In this review, we discuss several unique aspects of B cell responses that take place at local sites to combat acutely infectious and rapidly mutating influenza viruses.

Memory B Cells of Mice and Humans

We comprehensively review memory B cells (MBCs), covering the definition of MBCs and their identities and subsets, how MBCs are generated, where they are localized, how they are maintained, and how they are reactivated. Whereas naive B cells adopt multiple fates upon stimulation, MBCs are more restricted in their responses. Evolving work reveals that the MBC compartment in mice and humans consists of distinct subpopulations with differing effector functions. We discuss the various approaches to define subsets and subset-specific roles. A major theme is the need to both deliver faster effector function upon reexposure and readapt to antigenically variant pathogens while avoiding burnout, which would be the result if all MBCs generated only terminal effector function. We discuss cell-intrinsic differences in gene expression and signaling that underlie differences in function between MBCs and naive B cells and among MBC subsets and how this leads to memory responses.

Host differences in influenza-specific CD4 T cell and B cell responses are modulated by viral strain and route of immunization

The antibody response to influenza infection is largely dependent on CD4 T cell help for B cells. Cognate signals and secreted factors provided by CD4 T cells drive B cell activation and regulate antibody isotype switching for optimal antiviral activity. Recently, we analyzed HLA-DR1 transgenic (DR1) mice and C57BL/10 (B10) mice after infection with influenza virus A/New Caledonia/20/99 (NC) and defined epitopes recognized by virus-specific CD4 T cells. Using this information in the current study, we demonstrate that the pattern of secretion of IL-2, IFN-γ, and IL-4 by CD4 T cells activated by NC infection is largely independent of epitope specificity and the magnitude of the epitope-specific response. Interestingly, however, the characteristics of the virus-specific CD4 T cell and the B cell response to NC infection differed in DR1 and B10 mice. The response in B10 mice featured predominantly IFN-γ-secreting CD4 T cells and strong IgG2b/IgG2c production. In contrast, in DR1 mice most CD4 T cells secreted IL-2 and IgG production was IgG1-biased. Infection of DR1 mice with influenza PR8 generated a response that was comparable to that in B10 mice, with predominantly IFN-γ-secreting CD4 T cells and greater numbers of IgG2c than IgG1 antibody-secreting cells. The response to intramuscular vaccination with inactivated NC was similar in DR1 and B10 mice; the majority of CD4 T cells secreted IL-2 and most IgG antibody-secreting cells produced IgG2b or IgG2c. Our findings identify inherent host influences on characteristics of the virus-specific CD4 T cell and B cell responses that are restricted to the lung environment. Furthermore, we show that these host influences are substantially modulated by the type of infecting virus via the early induction of innate factors. Our findings emphasize the importance of immunization strategy for demonstrating inherent host differences in CD4 T cell and B cell responses.

Quantitative analysis of influenza virus-specific B cell memory generated by different routes of inactivated virus vaccination

We consider both Ab-secreting cell (ASC) and memory B cell (B(Mem)) populations in a quantitative analysis of virus-specific B cell memory generated by intramuscular or intranasal vaccination of mice with inactivated influenza virus. After both forms of vaccination, the memory phase was characterized by localization of ASCs in the bone marrow and dispersion of B(Mem) to organized lymphoid tissues. The stronger IgG response to intramuscular vaccination correlated with larger numbers of IgG ASCs in the bone marrow and IgG B(Mem). IgA production was only prominent in the response to intranasal vaccination and was associated with IgA ASC localization in the lung and IgA B(Mem) formation. Notably, few IgG ASCs or B(Mem) localized in the lung after intramuscular vaccination, in contrast to the situation following influenza pneumonia. Our analysis links the nature of immunization to characteristics of the state of B cell memory that may relate to protective immunity.

The generation of influenza-specific humoral responses is impaired in ST6Gal I-deficient mice

Posttranslational modification of proteins, such as glycosylation, can impact cell signaling and function. ST6Gal I, a glycosyltransferase expressed by B cells, catalyzes the addition of alpha-2,6 sialic acid to galactose, a modification found on N-linked glycoproteins such as CD22, a negative regulator of B cell activation. We show that SNA lectin, which binds alpha-2,6 sialic acid linked to galactose, shows high binding on plasma blasts and germinal center B cells following viral infection, suggesting ST6Gal I expression remains high on activated B cells in vivo. To understand the relevance of this modification on the antiviral B cell immune response, we infected ST6Gal I(-/-) mice with influenza A/HKx31. We demonstrate that the loss of ST6Gal I expression results in similar influenza infectivity in the lung, but significantly reduced early influenza-specific IgM and IgG levels in the serum, as well as significantly reduced numbers of early viral-specific Ab-secreting cells. At later memory time points, ST6Gal I(-/-) mice show comparable numbers of IgG influenza-specific memory B cells and long-lived plasma cells, with similarly high antiviral IgG titers, with the exception of IgG2c. Finally, we adoptively transfer purified B cells from wild-type or ST6Gal I(-/-) mice into B cell-deficient (microMT(-/-)) mice. Recipient mice that received ST6Gal I(-/-) B cells demonstrated reduced influenza-specific IgM levels, but similar levels of influenza-specific IgG, compared with mice that received wild-type B cells. These data suggest that a B cell intrinsic defect partially contributes to the impaired antiviral humoral response.

Broad dispersion and lung localization of virus-specific memory B cells induced by influenza pneumonia

Although memory B cells (B(Mem)) contribute significantly to resistance to infection, B(Mem) population characteristics that may relate to protective efficacy have received little attention. Here, we report a comprehensive quantitative analysis of virus-specific IgG and IgA B(Mem) dispersion after transient influenza pneumonia in mice. From early in the response, B(Mem) circulated continuously and dispersed widely to secondary lymphoid tissues. However, a complicated picture emerged with B(Mem) frequency differences between secondary lymphoid tissues indicating an influence of local tissue factors on trafficking. B(Mem) numbers increased and stabilized at tissue-specific frequencies without contraction of the B(Mem) pool during the period of analysis. The lung was notable as a nonsecondary lymphoid tissue where a rapid influx of IgG and IgA B(Mem) established relatively high frequencies that were maintained long term. Our findings provide insights into the pattern of B(Mem) dispersion, and emphasize the lung as a complex repository of immune memory after local infection.

Quantitative analysis of herpes simplex virus type 1-specific memory B cells generated by different routes of infection

We compared the herpes simplex virus type 1 (HSV)-specific memory B cell (MBC) populations generated by footpad and intranasal infection in mice. Both routes of infection generated transient antibody-secreting cell responses in the draining lymph nodes and spleen, and sustained circulating IgG. HSV-specific IgG MBCs, analyzed by limiting dilution assay approximately 8 weeks after infection, were distributed in a range of lymph nodes and in the spleen and Peyer's patches. Overall, the route of infection had little effect on the MBC frequency in each anatomical location. Interestingly, after both routes of infection there was a trend towards preferential MBC accumulation in the mediastinal lymph node. Intravaginal challenge of mice primed by footpad or intranasal infection generated similar secondary IgG responses. Our findings indicate that the widespread dispersion of MBCs to lymphoid tissues throughout the body is largely independent of the route of infection, but may be influenced by tissue-specific factors.