IL-6 Impairs Vaccine Responses in Neonatal Mice

State of pneumococcal vaccine immunity

Like the other invasive encapsulated bacteria, Streptococcus pneumoniae is also covered with a polysaccharide structure. Infants and elderly are most vulnerable to the invasive and noninvasive diseases caused by S. pneumoniae. Although antibodies against polysaccharide capsule are efficient in eliminating S. pneumoniae, the T cell independent nature of the immune response against polysaccharide vaccines renders them weakly antigenic. The introduction of protein conjugated capsular polysaccharide vaccines helped overcome the weak immunogenicity of pneumococcal polysaccharides and decreased the incidence of pneumococcal diseases, especially in pediatric population. Conjugate vaccines elicit T cell dependent response which involve the interaction of specialized CD4+ T cells, called follicular helper T cells (Tfh) with germinal center B cells in secondary lymphoid organs. Despite their improved immunogenicity, conjugate vaccines still need to be administered three to four times in infants during the first 15 month of their life because they mount poor Tfh response. Recent studies revealed fundamental differences in the generation of Tfh cells between neonates and adults. As the portfolio of pneumococcal conjugate vaccines continues to increase, better understanding of the mechanisms of antibody development in different age groups will help in the development of pneumococcal vaccines tailored for different ages.

Sustained antigen delivery improves germinal center reaction and increases antibody responses in neonatal mice

Neonates and young infants are known to have limited responses to pediatric vaccines due to reduced germinal center formation. Extended vaccine antigen dosing was previously shown to expand germinal center formation and improve humoral responses in adult mice. We report that sustained antigen delivery through sequential dosing overcomes neonatal limitations to form germinal center reactions and improves humoral immunity. Thus, vaccine strategies that extend the release of vaccine antigens may reduce the number of doses, and time needed, to achieve protective immunity in neonates and young infants.

IL6 suppresses vaccine responses in neonates by enhancing IL2 activity on T follicular helper cells

The inability of neonates to develop CD4+FoxP3-CXCR5hiPD-1hi T follicular helper (TFH) cells contributes to their weak vaccine responses. In previous studies, we measured diminished IgG responses when IL-6 was co-injected with a pneumococcal conjugate vaccine (PCV) in neonatal mice. This is in sharp contrast to adults, where IL-6 improves vaccine responses by downregulating the expression of IL-2Rβ on TFH cells and protecting them from the inhibitory effect of IL-2. In this study, we found that splenic IL-6 levels rapidly increased in both adult and neonatal mice following immunization, but the increase in neonatal mice was significantly more than that of adult mice. Moreover, immunized neonatal TFH cells expressed significantly more IL-2 as well as its receptors, IL-2Rα and IL-2Rβ, than the adult cells. Remarkably, IL-6 co-injection with PCV vaccine further increased the production of IL-2 and the expression of its receptors by neonatal TFH cells, whereas excess IL-6 had totally opposite effect in immunized adult mice. Underscoring the role of IL-6 in activating the IL-2 mediated suppression of vaccine responses, immunization of IL-6 knock-out neonates led to improved antibody responses accompanied by expanded TFH cells as well as lower levels of IL-2 and IL-2 receptors on TFH cells. Moreover, CpG containing PCV improved TFH response in neonates by suppressing the expression of IL-2 receptors on TFH cells and inhibiting IL-2 activity. These findings unveil age-specific differences in IL-6 mediated vaccine responses and highlight the need to consider age-related immunobiological attributes in designing vaccines.

C-type lectin receptor agonists elicit functional IL21-expressing Tfh cells and induce primary B cell responses in neonates

Introduction

C-type lectin receptor (CLR) agonists emerged as superior inducers of primary B cell responses in early life compared with Toll-like receptor (TLR) agonists, while both types of adjuvants are potent in adults.

Methods

Here, we explored the mechanisms accounting for the differences in neonatal adjuvanticity between a CLR-based (CAF®01) and a TLR4-based (GLA-SE) adjuvant administered with influenza hemagglutinin (HA) in neonatal mice, by using transcriptomics and systems biology analyses.

Results

On day 7 after immunization, HA/CAF01 increased IL6 and IL21 levels in the draining lymph nodes, while HA/GLA-SE increased IL10. CAF01 induced mixed Th1/Th17 neonatal responses while T cell responses induced by GLA-SE had a more pronounced Th2-profile. Only CAF01 induced T follicular helper (Tfh) cells expressing high levels of IL21 similar to levels induced in adult mice, which is essential for germinal center (GC) formation. Accordingly, only CAF01- induced neonatal Tfh cells activated adoptively transferred hen egg lysozyme (HEL)-specific B cells to form HEL+ GC B cells in neonatal mice upon vaccination with HEL-OVA.

Discussion

Collectively, the data show that CLR-based adjuvants are promising neonatal and infant adjuvants due to their ability to harness Tfh responses in early life.

Maternal infection causes dysfunctional BCR signaling in male offspring due to aberrant Xist expression

Infections during pregnancy with pathogens such as helminths correlate with altered immune responses to common childhood immunizations. However, the molecular mechanisms that underlie this remain unknown. Using our murine model of maternal schistosomiasis, when immunized, males from infected mothers had a lower frequency of antigen-specific germinal center B cells and downregulation of transcripts downstream of BCR signaling compared to males from uninfected mothers. This is driven by a reduction in developing B cell populations within the bone marrow of pups from infected mothers. Males from infected mothers were impacted to a greater extent than their female littermate counterparts. We found this defect to be caused by aberrant expression of the long non-coding RNA Xist in males leading to dysregulated Igα expression on developing B cells. This, for the first time, links dysfunctional BCR signaling with Xist expression, while also proposing a detrimental function for Xist expression in males.

Impaired long-term anti-HBs responses in choronic hepatitis C patients: Results from a five-year follow-up study with healthy control

Although hepatitis B virus (HBV) vaccination is recommended for hepatitis C virus (HCV)-infected individuals to avoid HBV superinfection, the persistence of their humoral and cell-mediated immunity responses to HBV vaccination is still under investigation. Patients with chronic hepatitis C (CHC) and matched healthy controls, who completed three doses of hepatitis B vaccine (HepB) in 2014, were followed up five years later. One booster dose of HepB was given to those with antibody against hepatitis B surface antigen (anti-HBs) lower than 10mIU/mL. Anti-HBs was tested at follow-up and on the 14th day after the booster dose, as well as HBsAg specific spot-forming cells of interferon γ and interleukin (IL) 2, 4, 5, and 6. At five years, only 56.58% of the CHC patients had sero-protective titers (≥10mIU/mL) of anti-HBs, compared to 70.83% in the controls (P < .05). Similarly, the geometric mean concentration (GMC) of anti-HBs in CHC patients was significantly lower than that in controls (16.95 vs 37.34 mIU/mL, P < .05). After the booster, both GMC and the rate of anamnestic response increased to a very high level in the two groups and the difference between them disappeared (P > .05). Multivariable analysis showed that HCV infection was an independent predictor factor to anti-HBs level at follow-up. HBsAg specific IL-6 was stronger in the CHC patients compared to the controls (P < .05). The data indicate that the durability of protective anti-HBs is poorer in CHC patients compared to healthy individuals, and impaired long-term anti-HBs responses might be associated with the increased HBsAg specific IL-6 responses.

B cell receptor-induced IL-10 production from neonatal mouse CD19+CD43- cells depends on STAT5-mediated IL-6 secretion

Newborns are unable to reach the adult-level humoral immune response partly due to the potent immunoregulatory role of IL-10. Increased IL-10 production by neonatal B cells has been attributed to the larger population of IL-10-producting CD43⁺ B-1 cells in neonates. Here, we show that neonatal mouse CD43^- non-B-1 cells also produce substantial amounts of IL-10 following B cell antigen receptor (BCR) activation. In neonatal mouse CD43^- non-B-1 cells, BCR engagement activated STAT5 under the control of phosphorylated forms of signaling molecules Syk, Btk, PKC, FAK, and Rac1. Neonatal STAT5 activation led to IL-6 production, which in turn was responsible for IL-10 production in an autocrine/paracrine fashion through the activation of STAT3. In addition to the increased IL-6 production in response to BCR stimulation, elevated expression of IL-6Rα expression in neonatal B cells rendered them highly susceptible to IL-6-mediated STAT3 phosphorylation and IL-10 production. Finally, IL-10 secreted from neonatal mouse CD43^- non-B-1 cells was sufficient to inhibit TNF-α secretion by macrophages. Our results unveil a distinct mechanism of IL-6-dependent IL-10 production in BCR-stimulated neonatal CD19⁺CD43^- B cells.

TLR agonists induce sustained IgG to hemagglutinin stem and modulate T cells following newborn vaccination

The newborn immune system is characterized by diminished immune responses that leave infants vulnerable to virus-mediated disease and make vaccination more challenging. Optimal vaccination strategies for influenza A virus (IAV) in newborns should result in robust levels of protective antibodies, including those with broad reactivity to combat the variability in IAV strains across seasons. The stem region of the hemagglutinin (HA) molecule is a target of such antibodies. Using a nonhuman primate model, we investigate the capacity of newborns to generate and maintain antibodies to the conserved stem region following vaccination. We find adjuvanting an inactivated vaccine with the TLR7/8 agonist R848 is effective in promoting sustained HA stem-specific IgG. Unexpectedly, HA stem-specific antibodies were generated with a distinct kinetic pattern compared to the overall response. Administration of R848 was associated with increased influenza-specific T follicular helper cells as well as Tregs with a less suppressive phenotype, suggesting adjuvant impacts multiple cell types that have the potential to contribute to the HA-stem response.

A comparative study of adjuvants effects on neonatal plasma cell survival niche in bone marrow and persistence of humoral immune responses

The neonatal immune system is distinct from the immune system of older individuals rendering neonates vulnerable to infections and poor responders to vaccination. Adjuvants can be used as tools to enhance immune responses to co-administered antigens. Antibody (Ab) persistence is mediated by long-lived plasma cells that reside in specialized survival niches in the bone marrow, and transient Ab responses in early life have been associated with decreased survival of plasma cells, possibly due to lack of survival factors. Various cells can secrete these factors and which cells are the main producers is still up for debate, especially in early life where this has not been fully addressed. The receptor BCMA and its ligand APRIL have been shown to be important in the maintenance of plasma cells and Abs. Herein, we assessed age-dependent maturation of a broad range of bone marrow accessory cells and their expression of the survival factors APRIL and IL-6. Furthermore, we performed a comparative analysis of the potential of 5 different adjuvants; LT-K63, mmCT, MF59, IC31 and alum, to enhance expression of survival factors and BCMA following immunization of neonatal mice with tetanus toxoid (TT) vaccine. We found that APRIL expression was reduced in the bone marrow of young mice whereas IL-6 expression was higher. Eosinophils, macrophages, megakaryocytes, monocytes and lymphocytes were important secretors of survival factors in early life but undefined cells also constituted a large fraction of secretors. Immunization and adjuvants enhanced APRIL expression but decreased IL-6 expression in bone marrow cells early after immunization. Furthermore, neonatal immunization with adjuvants enhanced the proportion of plasmablasts and plasma cells that expressed BCMA both in spleen and bone marrow. Enhanced BCMA expression correlated with enhanced vaccine-specific humoral responses, even though the effect of alum on BCMA was less pronounced than those of the other adjuvants at later time points. We propose that low APRIL expression in bone marrow as well as low BCMA expression of plasmablasts/plasma cells in early life together cause transient Ab responses and could represent targets to be triggered by vaccine adjuvants to induce persistent humoral immune responses in this age group.

Targeted Delivery of Nanovaccine to Dendritic Cells via DC-Binding Peptides Induces Potent Antiviral Immunity in vivo

Background

Methods

Results

Conclusion

Effect of Dietary Bacillus licheniformis Supplementation on Growth Performance and Microbiota Diversity of Pekin Ducks

This experiment was conducted to investigate the effects of different concentrations of Bacillus licheniformis (B. licheniformis) on growth performance and microbiota diversity of Pekin ducks. Three hundred 1-day-old healthy Pekin ducks were randomly divided into 5 groups with 6 replicates per group and 10 ducks per replicate. The five treatments supplemented with basal diets containing: either 0 (group CON), 200 (group LLB), 400 (group MLB), and 800 (group HLB) mg/kg B. licheniformis or 150 mg/kg aureomycin (group ANT) for 42 days, respectively, and were sacrificed and sampled in the morning of the 42nd day for detection of relevant indexes. The results showed as follows: The feed conversion ratio of the LLB group and MLB groups were lower than the CON group (P < 0.05). The body weight and average daily feed intake of the MLB group were significantly higher than that of the CON group and ANT group (P < 0.05). Compared with the CON group, the MLB group significantly increased the content of IgA (P < 0.05) and proinflammatory IL-6 were significantly decreased (P < 0.05), besides, the activity of SOD and T-AOC were also significantly increased in the MLB group (P < 0.05). The 16S rRNA analysis showed that B. licheniformis treatments had no effect (P > 0.05) on the alpha diversities of the intestine. The addition of B. licheniformis had a dynamic effect on the abundance of cecal microflora of Pekin ducks, and 1-21 d increased the diversity of microflora, while 21d-42 d decreased it. Compared with the CON group, the relative abundance of Epsilonbacteraeota in the MLB group was significantly increased on Day 21 (P < 0.05), and that of Tenericutes in the LLB group was significantly increased as well (P < 0.05). At 42 d, the relative abundance of Bacteroidetes in LLB, MBL, HBL, and ANT groups was significantly increased (P < 0.05). In addition, the addition of B. licheniformis increased the amount of SCAF-producing bacteria in the intestinal microbiota, such as Lachnospiraceae, Collinsella, Christensenellaceae, and Bilophila. The PICRUSt method was used to predict the intestinal microbiota function, and it was found that lipid transport and metabolism of intestinal microbiota in the MLB group were significantly affected. Overall, these results suggest diet supplemented with B. licheniformis improved growth performance, immune status, antioxidant capacity, and modulated intestinal microbiota in Pekin ducks. The optimal dietary supplement dose is 400 mg/kg.

Understanding Antibody Responses in Early Life: Baby Steps towards Developing an Effective Influenza Vaccine

The immune system of young infants is both quantitatively and qualitatively distinct from that of adults, with diminished responsiveness leaving these individuals vulnerable to infection. Because of this, young infants suffer increased morbidity and mortality from respiratory pathogens such as influenza viruses. The impaired generation of robust and persistent antibody responses in these individuals makes overcoming this increased vulnerability through vaccination challenging. Because of this, an effective vaccine against influenza viruses in infants under 6 months is not available. Furthermore, vaccination against influenza viruses is challenging even in adults due to the high antigenic variability across viral strains, allowing immune evasion even after induction of robust immune responses. This has led to substantial interest in understanding how specific antibody responses are formed to variable and conserved components of influenza viruses, as immune responses tend to strongly favor recognition of variable epitopes. Elicitation of broadly protective antibody in young infants, therefore, requires that both the unique characteristics of young infant immunity as well as the antibody immunodominance present among epitopes be effectively addressed. Here, we review our current understanding of the antibody response in newborns and young infants and discuss recent developments in vaccination strategies that can modulate both magnitude and epitope specificity of IAV-specific antibody.

Coronavirus-specific antibody production in middle-aged mice requires phospholipase A2G2D

Worse outcomes occur in aged compared with young populations after infections with respiratory viruses, including pathogenic coronaviruses (SARS-CoV, MERS-CoV, and SARS-CoV-2), and are associated with a suboptimal lung milieu ("inflammaging"). We previously showed that a single inducible phospholipase, PLA2G2D, is associated with a proresolving/antiinflammatory response in the lungs, and increases with age. Survival was increased in naive Pla2g2d-/- mice infected with SARS-CoV resulting from augmented respiratory dendritic cell (rDC) activation and enhanced priming of virus-specific T cells. Here, in contrast, we show that intranasal immunization provided no additional protection in middle-aged Pla2g2d-/- mice infected with any of the 3 pathogenic human coronaviruses because virtually no virus-specific antibodies or follicular helper CD4+ T (Tfh) cells were produced. Using MERS-CoV-infected mice, we found that these effects did not result from T or B cell intrinsic factors. Rather, they resulted from enhanced, and ultimately, pathogenic rDC activation, as manifested most prominently by enhanced IL-1β expression. Wild-type rDC transfer to Pla2g2d-/- mice in conjunction with partial IL-1β blockade reversed this defect and resulted in increased virus-specific antibody and Tfh responses. Together, these results indicate that PLA2G2D has an unexpected role in the lungs, serving as an important modulator of rDC activation, with protective and pathogenic effects in respiratory coronavirus infections and immunization, respectively.

Impacts of ceftriaxone exposure during pregnancy on maternal gut and placental microbiota and its influence on maternal and offspring immunity in mice

This study aimed to investigate the association between microbiota found in the maternal gut and placenta, and whether ceftriaxone exposure during pregnancy could alter these microbiota, and consequently affect the immunity of the mothers and their offspring. The microbiota in the feces and placenta of the dams were comprehensively analyzed using16S rRNA sequencing. Furthermore, viable bacteria in the placentas and blood of pups were also isolated by plate cultivation then taxonomically identified in detail by clone sequencing. Serum cytokines collected from dams and pups were quantitatively profiled using Luminex. The spleen organ index of dams was significantly lower and the offspring serum interleukin-6 levels were significantly higher in ceftriaxone-treated mice compared with the control group. The maternal fecal microbiota community was drastically altered in ceftriaxone-treated mice with significantly decreased diversity, depletion of Bacteroidetes and the blooming of Tenericutes. However, the placenta microbiota was dominated by Proteobacteria especially characteristically by Ralstonia, which was distinct from the maternal gut microbiota, regardless of whether ceftriaxone treatment or not. Viable bacteria have been found in placenta and blood cultures. These results indicated that ceftriaxone exposure in pregnancy could dramatically alter maternal intestinal microbiota, which affected the immunity of the mothers and their offspring at least partly, characteristically by enhanced pro-inflammatory responses. This study also indicated that the placenta might harbor its own microbes and the microbes were distinct from maternal gut microbiota, which may not be affected by oral administration of ceftriaxone during pregnancy.

Comparison of flagellin and an oil-emulsion adjuvant in inactivated Newcastle disease vaccine in stimulation of immunogenic parameters

The present study was designed to investigate the potential application of native (N) and recombinant (truncated modified [tmFliC] and full-length [flFliC]) flagellin proteins along with inactivated Newcastle disease virus (NDV). Fifty six SPF chickens were immunized twice with PBS (control), inactivated NDV (Ag), inactivated NDV/flFliC (AgF), inactivated NDV/tmFliC (AgT), inactivated NDV/N (AgN), commercial vaccine containing Montanide (Vac) and Vac/N (VacN), with a two-week interval. Blood was collected weekly and spleens were harvested after chickens were sacrificed. Interleukin-6 (IL-6) and tumor necrotic factor-α (TNF-α) gene expression in peripheral blood mononuclear cells were analyzed by Real-Time PCR. Antibody response was assessed by haemagglutination inhibition (HI). Cellular activity was quantified by MTT assay. Results showed that the most IL-6 and TNF-α gene expression was observed in AgF group (P < 0.01). The lowest gene expression among vaccinated groups was observed in Ag group for IL-6 and Ag and Vac group for TNF-α. The highest HI titer was observed in Vac, VacN, AgF and AgT groups. The AgF group showed the highest cellular activity (P < 0.01). In conclusion, flagellin-adjuvanted groups showed a pro-inflammatory effect and acted similarly to or better than the Vac group. Hence, flagellin can be proposed as a potential adjuvant for ND vaccine.

Neonatal mice resist Plasmodium yoelii infection until exposed to para-aminobenzoic acid containing diet after weaning

We developed a newborn (NB) mouse Plasmodium yoelii NL infection model to study malaria in early age. Surprisingly, the onset of parasitemia in P. yoelii challenged NB mice was delayed compared to adults and coincided with the weaning date when weanlings switched from maternal milk to normal chow diet. Also, compared to adult mice, parasitemia resolved much later (48 days vs 20 days post challenge) and the peak parasitemia was twice as high in weanlings. Concurrently, weanlings’ germinal center reaction was delayed and diminished compared to adult mice. Maternal milk is deficient in para-aminobenzoic acid (PABA), which is required for de novo folate synthesis by Plasmodium. Suggesting a possible role for the protection afforded by PABA-deficient maternal milk, mice fed with a PABA-deficient diet after the weaning continued to control parasitemia. Despite the reduced parasitemia, these mice developed robust T follicular helper (Tfh) responses and were protected from a second P. yoelii challenge. The NB malaria model provides mechanistic insight into the human infant malaria manifestations where a diet solely based on breast-feeding reduces the incidence of severe malaria in infants. NB mice experiments also support further studies to investigate dietary PABA restriction in the management of severe malaria in infants.

Influenza virus neuraminidase regulates host CD8+ T-cell response in mice

Influenza A virus (IAV)-specific CD8⁺ T-cell response was shown to provide protection against pandemic and seasonal influenza infections. However, the response was often relatively weak and the mechanism was unclear. Here, we show that the composition of IAV released from infected cells is regulated by the neuraminidase (NA) activity and the cells infected by NA-defective virus cause intracellular viral protein accumulation and cell death. In addition, after uptake of NA-defective viruses by dendritic cells (DCs), an expression of the major histocompatibility complex class I is induced to activate IAV-specific CD8⁺ T-cell response. When mice were infected by NA-defective IAV, a CD8⁺ T-cell response to the highly conserved viral antigens including PB1, NP, HA, M1, M2 and NS1 was observed along with the increasing expression of IL10, IL12 and IL27. Vaccination of mice with NA-defective H1N1 A/WSN/33 induced a strong IAV-specific CD8⁺ T cell response against H1N1, H3N2 and H5N1. This study reveals the role of NA in the IAV-specific CD8⁺ T-cell response and virion assembly process, and provides an alternative direction toward the development of universal influenza vaccines.

Protective Intranasal Immunization Against Influenza Virus in Infant Mice Is Dependent on IL-6

Respiratory diseases adversely affect infants and are the focus of efforts to develop vaccinations and other modalities to prevent disease. The infant immune system differs from that of older children and adults in many ways that are as yet ill understood. We have used a C57BL/6 mouse model of infection with a laboratory- adapted strain of influenza (PR8) to delineate the importance of the cytokine IL-6 in the innate response to primary infection and in the development of protective immunity in adult mice. Herein, we used this same model in infant (14 days of age) mice to determine the effect of IL-6 deficiency. Infant wild type mice are more susceptible than older mice to infection, similar to the findings in humans. IL-6 is expressed in the lung in the early response to PR8 infection. While intramuscular immunization does not protect against lethal challenge, intranasal administration of heat inactivated virus is protective and correlates with expression of IL-6 in the lung, activation of lung CD8 cells, and development of an influenza-specific antibody response. In IL-6 deficient mice, this response is abrogated, and deficient mice are not protected against lethal challenge. These studies support the importance of the role of the tissue environment in infant immunity, and further suggest that IL-6 may be helpful in the generation of protective immune responses in infants.