Somatic mutation of immunoglobulin V(H)6 genes in human infants

Early-life risk factors which govern pro-allergic immunity

Allergic diseases affect up to 40% of the global population with a substantial rise in food allergies, in particular, over the past decades. For the majority of individuals with allergy fundamental programming of a pro-allergic immune system largely occurs in early childhood where it is crucially governed by prenatal genetic and environmental factors, including their interactions. These factors include several genetic aberrations, such as filaggrin loss-of-function mutations, early exposure to respiratory syncytial virus, and various chemicals such as plasticizers, as well as the influence of the gut microbiome and numerous lifestyle circumstances. The effects of such a wide range of factors on allergic responses to an array of potential allergens is complex and the severity of these responses in a clinical setting are subsequently not easy to predict at the present time. However, some parameters which condition a pro-allergic immune response, including severe anaphylaxis, are becoming clearer. This review summarises what we currently know, and don't know, about the factors which influence developing pro-allergic immunity particularly during the early-life perinatal period.

Ear Molding for Congenital Auricular Deformities: Efficacy and Factors Affecting Outcomes

Objective: This study's aim was to assess the effectiveness of ear molding for congenital auricular deformities, analyze the factors affecting prognosis, and provide more clinical data supporting nonsurgical correction for this condition. Methods: A prospective study of a consecutive series of infants treated with ear molding from January 2021 to December 2022 in the department of otolaryngology, Second Affiliated Hospital of Harbin Medical University, was conducted. Demographic and clinical information were collected, and photographs of the ear were taken before and after treatment. Treatment efficacy and the relevant influencing factors were evaluated. Results: Thirty-five patients, including 59 with congenital ear anomalies, underwent noninvasive ear molding. The deformity type, treatment initiation age, and number of treatment cycles affected treatment efficacy. Earlier treatment initiation was associated with a shorter treatment period. Treatments were started earlier if decision-makers were more anxious. Conclusion: The earlier the neonatal auricle deformity is treated, the shorter the treatment time and the more ideal the clinical effect will be. Early noninvasive treatment for microtia is valuable. Early detection and parental awareness and education can help children receive treatment earlier and improve the success rate.

Early Appearance of Functional Plasma Cells (CD138+CD98+) in Non-immunized Neonate Mice

Plasma cells (PCs) are terminally differentiated antibody-secreting cells, derived from activated B-lymphocytes in response to either T-independent or T-dependent antigens. The plasma cell population is scarce in circulation in non-immunized individuals. It is established that neonates are incapable of mounting an efficient immune response due to the immaturity of the immune system. However, this disadvantage is well overcome through the antibodies neonates receive from breastmilk. This implies that neonates will be only protected against antigens the mother had previously encountered. Thus, the child might be potentially susceptible to new antigens. This issue prompted us to seek for the presence of PCs in non-immunized neonate mice. We found a PC population identified as CD138+/CD98+ cells since day one after birth. These PCs were positive for Ki67 and expressed Blimp-1, B220, and CD19, which suggests the populations are plasmablasts and PCs with heterogeneous phenotype. These PCs were also determined to secrete antibodies, although mainly isotype IgM. Altogether, the results indicated that neonate PCs can produce antibodies against antigens they encounter in the first weeks of life, most likely coming from food, colonizing microbiota, or the environment.

B cell repertoire in children with skin barrier dysfunction supports altered IgE maturation associated with allergic food sensitization

The skin is a major immune organ and skin barrier dysfunction is a major risk factor for the development of the inappropriate immune response seen in allergic disease. Skin barrier disruption alters the landscape of antigens experienced by the immune system and the downstream impacts on the antibody repertoire remain poorly characterized, particularly for the IgE isotype responsible for allergic specificity and in early life, when allergic disease is developing. In this study, we sequenced antibody gene repertoires from a large and well-characterized cohort of children with atopic dermatitis and found that food sensitization was associated with lower mutation frequencies in the IgE compartment. This trend was abrogated in children living with pets during the first year of life. These results elucidate potential molecular mechanisms underlying the protective effects of pet ownership and non-antiseptic environs reported for allergic disease, and the hygiene hypothesis more broadly. We also observed increased IgE diversity and increased isotype-switching to the IgE isotype, suggesting that B cell development, particularly isotype-switching, is heavily altered in the those with food allergen sensitizations relative to those without food allergen sensitizations. Unlike for food antigens, aeroallergen sensitization exhibited no effect on IgE mutation or diversity. Consistent patterns of antibody rearrangement were associated with food allergen sensitization in subjects with atopic dermatitis. Thus, we propose the Immune Repertoire in Atopic Disease (IRAD) score, to quantify this repertoire shift and to aid clinically in patient diagnosis and risk stratification.

Ontogeny of the B Cell Receptor Repertoire and Microbiome in Mice

The immune system matures throughout childhood to achieve full functionality in protecting our bodies against threats. The immune system has a strong reciprocal symbiosis with the host bacterial population and the two systems co-develop, shaping each other. Despite their fundamental role in health physiology, the ontogeny of these systems is poorly characterized. In this study, we investigated the development of the BCR repertoire by analyzing high-throughput sequencing of their receptors in several time points of young C57BL/6J mice. In parallel, we explored the development of the gut microbiome. We discovered that the gut IgA repertoires change from birth to adolescence, including an increase in CDR3 lengths and somatic hypermutation levels. This contrasts with the spleen IgM repertoires that remain stable and distinct from the IgA repertoires in the gut. We also discovered that large clones that germinate in the gut are initially confined to a specific gut compartment, then expand to nearby compartments and later on expand also to the spleen and remain there. Finally, we explored the associations between diversity indices of the B cell repertoires and the microbiome, as well as associations between bacterial and BCR clusters. Our results shed light on the ontogeny of the adaptive immune system and the microbiome, providing a baseline for future research.

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.

Longitudinal analysis of total serum IgE levels with allergen sensitization and atopic diseases in early childhood

There are few studies addressing the longitudinal analysis of serum IgE levels and its impact to the development of atopic diseases in early childhood. We investigated 170 children who regularly followed up at our clinic for 4 years in a birth cohort study with at least 3 time-points of serum samples. The pattern of total serum IgE levels from 6 months to 4 years of age was clustered using K-means method in R software. Specific immunoglobulin E antibodies against food (egg white and milk) and inhalant allergens (D. pteronyssinus and D. farinae) were measured at 0.5, 1, 1.5, 2, 3 and 4 years of age. By using K-means clustering, the dynamic changes in serum IgE levels was significantly stratified into 3 clusters (cluster A, < 100 kU/L, n = 106; cluster B, 100–200 kU/L, n = 35; cluster C, ≥ 200 kU/L, n = 29). A persistent total IgE levels higher than 100 kU/L appeared to be associated with higher prevalence of sensitization to food but not mite. However, a persistent IgE levels higher than 200 kU/L was not only remarkably related to increased prevalence of mite sensitization, but also risk of eczema at age 1 and allergic rhinitis and asthma at age 2, 3 and 4. In conclusion, a persistent total serum IgE level ≥ 200 kU/L since infancy is strongly associated with the presence of food and mite sensitization, as well as the development of eczema in infants, and rhinitis and asthma later in early childhood.

Nanoparticle vaccines against respiratory syncytial virus

Respiratory syncytial virus (RSV) is a leading cause of respiratory disease in infants, the elderly and immunocompromised individuals. Despite the global burden, there is no licensed vaccine for RSV. Recent advances in the use of nanoparticle technology have provided new opportunities to address some of the limitations of conventional vaccines. Precise control over particle size and surface properties enhance antigen stability and prolong antigen release. Particle size can also be modified to target specific antigen-presenting cells in order to induce specific types of effector T-cell responses. Numerous nanoparticle-based vaccines are currently being evaluated for RSV including inorganic, polymeric and virus-like particle-based formulations. Here, we review the potential advantages of using different nanoparticle formulations in a vaccine for RSV, and discuss many examples of safe, and effective vaccines currently in both preclinical and clinical stages of testing.

Efficacy of Ear Molding in Infants using the EarWell Infant Correction System and Factors Affecting Outcome

BACKGROUND

One-third of infants have ear anomalies, and less than one-third self-correct. Correction of ear deformities by molding exploits the plasticity of the auricular cartilage because of circulating maternal estrogen during infancy. In this study, the authors assess the efficacy of the EarWell Infant Correction System in the correction of ear deformities and determine the factors that affect its outcome.

METHODS

The authors conducted a single-center prospective study over a 3-year period. Consecutive full-term infants who underwent ear molding with the EarWell system were recruited. Primary outcome was successful correction of ear anomaly. Secondary outcomes included complications and maintenance of ear shape. Factors identified included type of anomaly, age at application, duration of application, and breastfeeding.

RESULTS

Sixty-seven patients with a total of 105 ears were recruited. The anomalies were classified into deformations (66.7 percent) and malformations (33.3 percent). The median age group at presentation was 0 to 7 days (67 percent). Average duration of application was 4.1 weeks. Successful correction was achieved in 86 percent of patients. Ear deformations achieved a significantly higher rate of successful outcome (98 percent) compared with malformations (64 percent) (p < 0.001). Skin complications were common (46 percent) and attributed to our tropical climate. Patients with complications were of a higher mean age (22.1 days) compared with patients with no complications (10.6 days) (p = 0.037).

CONCLUSIONS

The EarWell system is an effective nonsurgical option for the treatment of ear anomalies. The type of anomaly was the only predictor of successful correction, whereas age at application, duration of molding, and breastfeeding were not. Complications were more common in older infants.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

New technologies and applications in infant B cell immunology

The human immune system changes dramatically with age, and early life exposures to pathogens and environmental antigens begin the formation of immune memory which influences subsequent responses later in life. To study infant immunity, sample-sparing experimental methods that extract maximal data from small samples of blood or other tissues are needed; fortunately, recent developments in high-throughput sequencing and multiplexed labeling and measurement of markers on cells are well-suited to these tasks. Here, we review some recent studies of infant immune responses to infectious disease, highlighting similarities and differences between infants and adults, and identifying important questions for future research. Recent clinical trials in food allergy have revealed the critical role of immunological events in the first year of life that determine an individual's risk of developing peanut allergy; these also warrant thorough evaluation using the new immune monitoring tools.

Factors influencing the induction of high affinity antibodies to Plasmodium falciparum merozoite antigens and how affinity changes over time

Understanding the functional characteristics of naturally acquired antibodies against P. falciparum merozoite antigens is crucial for determining the protective functions of antibodies. Affinity (measured as k_d) of naturally acquired antibodies against two key targets of acquired immunity, EBA175 and PfRh2, was determined using Surface Plasmon Resonance (SPR) in a longitudinal survey in Nigeria. A majority of the participants, 79% and 67%, maintained stable antibody affinities to EBA175 and PfRh2, respectively, over time. In about 10% of the individuals, there was a reciprocal interaction with a reduction over time in antibody affinity for PfRh2 and an increase for EBA175. In general, PfRh2 elicited antibodies with higher affinity compared to EBA175. Individuals with higher exposure to malaria produced antibodies with higher affinity to both antigens. Younger individuals (5–15 years) produced comparable or higher affinity antibodies than adults (>15 years) against EBA175, but not for PfRh2. Correlation between total IgG (ELISA) and affinity varied between individuals, but PfRh2 elicited antibodies with a higher correlation in a majority of the participants. There was also a correlation between antibody inhibition of erythrocyte invasion by merozoites and PfRh2 affinity. This work gives new insights into the generation and maintenance of antibody affinity over time.

The evolution of greater humoral immunity in females than males: implications for vaccine efficacy

Males and females differ in their effector and memory immune responses to foreign and self-antigens. The difference in antibody responses (i.e., humoral immunity), in particular, is one of the most well conserved sex differences in immunology. Certain sex differences in humoral immunity are present throughout life, whereas others are only apparent after puberty and prior to reproductive senescence, suggesting that both genes and hormones are involved. Importantly, these sex-based differences in humoral immunity contribute to variation in the responses to vaccines and may explain some disparities in vaccine efficacy between the sexes. Elevated humoral immunity in females compared with males is phylogenetically well conserved, suggesting an adaptive advantage of elevated antibody for reproductive success, including for the transfer of protective antibodies to offspring.

Infants Infected with Respiratory Syncytial Virus Generate Potent Neutralizing Antibodies that Lack Somatic Hypermutation

Respiratory syncytial virus (RSV) is a leading cause of infant mortality, and there are currently no licensed vaccines to protect this vulnerable population. A comprehensive understanding of infant antibody responses to natural RSV infection would facilitate vaccine development. Here, we isolated more than 450 RSV fusion glycoprotein (F)-specific antibodies from 7 RSV-infected infants and found that half of the antibodies recognized only two antigenic sites. Antibodies targeting both sites showed convergent sequence features, and structural studies revealed the molecular basis for their recognition of RSV F. A subset of antibodies targeting one of these sites displayed potent neutralizing activity despite lacking somatic mutations, and similar antibodies were detected in RSV-naive B cell repertoires, suggesting that expansion of these B cells in infants may be possible with suitably designed vaccine antigens. Collectively, our results provide fundamental insights into infant antibody responses and a framework for the rational design of age-specific RSV vaccines.

Factors Affecting the Immunity to Respiratory Syncytial Virus: From Epigenetics to Microbiome

Respiratory syncytial virus (RSV) is a common pathogen that infects virtually all children by 2 years of age and is the leading cause of hospitalization of infants worldwide. While most children experience mild symptoms, some children progress to severe lower respiratory tract infection. Those children with severe disease have a much higher risk of developing childhood wheezing later in life. Many risk factors are known to result in exacerbated disease, including premature birth and early age of RSV infection, when the immune system is relatively immature. The development of the immune system before and after birth may be altered by several extrinsic and intrinsic factors that could lead to severe disease predisposition in children who do not exhibit any currently known risk factors. Recently, the role of the microbiome and the resulting metabolite profile has been an area of intense study in the development of lung disease, including viral infection and asthma. This review explores both known risk factors that can lead to severe RSV-induced disease as well as emerging topics in the development of immunity to RSV and the long-term consequences of severe infection.

Accurate immune repertoire sequencing reveals malaria infection driven antibody lineage diversification in young children

Accurately measuring antibody repertoire sequence composition in a small amount of blood is challenging yet important for understanding repertoire responses to infection and vaccination. We develop molecular identifier clustering-based immune repertoire sequencing (MIDCIRS) and use it to study age-related antibody repertoire development and diversification before and during acute malaria in infants (< 12 months old) and toddlers (12-47 months old) with 4-8 ml of blood. Here, we show this accurate and high-coverage repertoire-sequencing method can use as few as 1000 naive B cells. Unexpectedly, we discover high levels of somatic hypermutation in infants as young as 3 months old. Antibody clonal lineage analysis reveals that somatic hypermutation levels are increased in both infants and toddlers upon infection, and memory B cells isolated from individuals who previously experienced malaria continue to induce somatic hypermutations upon malaria rechallenge. These results highlight the potential of antibody repertoire diversification in infants and toddlers.Somatic hypermutation of antibodies can occur in infants but are difficult to track. Here the authors present a new method called MIDCIRS for deep quantitative repertoire sequencing with few cells, and show infants as young as 3 months can expand antibody lineage complexity in response to malaria infection.

Microbiology laboratory and the management of mother-child varicella-zoster virus infection

Varicella-zoster virus, which is responsible for varicella (chickenpox) and herpes zoster (shingles), is ubiquitous and causes an acute infection among children, especially those aged less than six years. As 90% of adults have had varicella in childhood, it is unusual to encounter an infected pregnant woman but, if the disease does appear, it can lead to complications for both the mother and fetus or newborn. The major maternal complications include pneumonia, which can lead to death if not treated. If the virus passes to the fetus, congenital varicella syndrome, neonatal varicella (particularly serious if maternal rash appears in the days immediately before or after childbirth) or herpes zoster in the early years of life may occur depending on the time of infection. A Microbiology laboratory can help in the diagnosis and management of mother-child infection at four main times: (1) when a pregnant woman has been exposed to varicella or herpes zoster, a prompt search for specific antibodies can determine whether she is susceptible to, or protected against infection; (2) when a pregnant woman develops clinical symptoms consistent with varicella, the diagnosis is usually clinical, but a laboratory can be crucial if the symptoms are doubtful or otherwise unclear (atypical patterns in immunocompromised subjects, patients with post-vaccination varicella, or subjects who have received immunoglobulins), or if there is a need for a differential diagnosis between varicella and other types of dermatoses with vesicle formation; (3) when a prenatal diagnosis of uterine infection is required in order to detect cases of congenital varicella syndrome after the onset of varicella in the mother; and (4) when the baby is born and it is necessary to confirm a diagnosis of varicella (and its complications), make a differential diagnosis between varicella and other diseases with similar symptoms, or confirm a causal relationship between maternal varicella and malformations in a newborn.

Adjuvanting an inactivated influenza vaccine with flagellin improves the function and quantity of the long-term antibody response in a nonhuman primate neonate model

Young infants are at significantly increased risk of developing severe disease following infection with influenza virus. At present there is no approved vaccine for individuals below the age of six months given previous studies showing a failure of these individuals to efficiently seroconvert. Given the major impact of influenza on infant health, it is critical that we develop vaccines that will be safe and effective in this population. Using a nonhuman primate (NHP) model, we have evaluated the ability of an inactivated influenza virus vaccine adjuvanted with flagellin to result in long term immune responses in neonates. To evaluate this critical attribute, neonate NHP were vaccinated and boosted with inactivated influenza virus in combination with either flagellin or a mutant inactive flagellin control. Our studies show that inclusion of flagellin resulted in a significant increase (5-fold, p=0.04) in influenza virus-specific IgG antibody at 6months post-vaccination. In addition, the antibody present at this late time was of higher affinity (2.4-fold, p=0.02). Finally a greater percentage of infants had detectable neutralizing antibody. These results support the use of flagellin in neonates as an adjuvant that promotes long-lived, high affinity antibody responses.

Evolution of the immune system in humans from infancy to old age

This article reviews the development of the immune response through neonatal, infant and adult life, including pregnancy, ending with the decline in old age. A picture emerges of a child born with an immature, innate and adaptive immune system, which matures and acquires memory as he or she grows. It then goes into decline in old age. These changes are considered alongside the risks of different types of infection, autoimmune disease and malignancy.

Development of immunity in early life

The immune system in early life goes through rapid and radical changes. Early life is also the period with the highest risk of infections. The foetal immune system is programmed to coexist with foreign antigenic influences in utero, and postnatally to rapidly develop a functional system capable of distinguishing helpful microbes from harmful pathogens. Both host genetics and environmental influences shape this dramatic transition and direct the trajectory of the developing immune system into early childhood and beyond. Given the malleability of the immune system in early life, interventions aimed at modulating this trajectory thus have the potential to translate into considerable reductions in infectious disease burden with immediate as well as long-lasting benefit. However, an improved understanding of the underlying molecular drivers of early life immunity is prerequisite to optimise such interventions and transform the window of early life vulnerability into one of opportunity.

Assessment of antibody level and avidity against Bordetella pertussis in a cohort of Egyptian individuals aged 1-18 years

Pertussis specific antibodies were studied with respect to quality and quantity in a cohort of apparently healthy Egyptian children and adolescents, with their age range between 1 and 18 years, in an attempt to get a close and clear insight into the current humoral immunization status in this specified group and to try find a relation between the antibody levels and their avidities in eradication of this devastating infectious disease. Our results showed that avidity increase was most marked in young school children (6–8 years) where it seemed to reach a plateau in older children and adolescents. Antibody titer was highest in toddlers (1–2 years) and young school children (6–8 years) groups, most probably following vaccination and/or booster doses. Among children aged 1–5 years, 28% had highly avid and 50% had high titer antibodies, whereas in adolescents aged 13–18 years, 70% had highly avid antibodies and only 30% had high titer antibodies. The results clearly demonstrated that while levels of anti-Bordetella pertussis (B. pertussis) antibodies wane with growing age, the avidity seems to increase, to a plateau, irrespective of further antigen exposure in a pattern showing complete independence of avidity on concentration. The present study draws attention to the importance of avidity measurements, together with conventional ELISAs, for evaluating immunity against pertussis. Being based on a limited sample size, it could open doors for larger-scale surveys to be possible indicators for the need and timing of booster vaccination doses among Egyptians.

Is Infant Immunity Actively Suppressed or Immature?

Almost 7 million children under the age 5 die each year, and most of these deaths are attributable to vaccine-preventable infections. Young infants respond poorly to infections and vaccines. In particular, dendritic cells secrete less IL-12 and IL-18, CD8^pos T cells and NK cells have defective cytolysis and cytokine production, and CD4^pos T cell responses tend to bias towards a Th2 phenotype and promotion of regulatory T cells (T_regs). The basis for these differences is not well understood and may be in part explained by epigenetic differences, as well as immaturity of the infant's immune system. Here we present a third possibility, which involves active suppression by immune regulatory cells and place in context the immune suppressive pathways of mesenchymal stromal cells (MSC), myeloid-derived suppressor cells (MDSC), CD5^pos B cells, and T_regs. The immune pathways that these immune regulatory cells inhibit are similar to those that are defective in the infant. Therefore, the immune deficiencies seen in infants could be explained, in part, by active suppressive cells, indicating potential new avenues for intervention.

Effect of multivitamin supplementation on measles vaccine response among HIV-exposed uninfected Tanzanian infants

Immunization and nutritional interventions are mainstays of child health programs in sub-Saharan Africa, yet few published data exist on their interactions. HIV-exposed (but uninfected) infants enrolled in a randomized placebo-controlled trial of multivitamin supplements (vitamins B complex, C, and E) conducted in Tanzania were sampled for an assessment of measles IgG quantity and avidity at 15 to 18 months. Infants were vaccinated between 8.5 and 12 months of age, and all mothers received high-dose multivitamins as the standard of care. Of 201 HIV-exposed infants who were enrolled, 138 (68.7%) were seropositive for measles. There were no effects of infant multivitamin supplementation on measles seroconversion proportions, IgG concentrations, or IgG avidity (P > 0.05). The measles seroconversion proportion was greater for HIV-exposed infants vaccinated at 10 to 11 months of age than for those vaccinated at 8.5 to 10 months (P = 0.032) and greater for infants whose mothers had a CD4 T-cell count of <200 cells/μl than for infants whose mothers had a CD4 T-cell count of >350 cells/μl (P = 0.039). Stunted infants had a significantly decreased IgG quantity compared to nonstunted infants (P = 0.012). As for measles avidity, HIV-exposed infants vaccinated at 10 to 11 months had increased antibody avidity compared to those vaccinated at 8.5 to 10 months (P = 0.031). Maternal CD4 T-cell counts of <200 cells/μl were associated with decreased avidity compared to counts of >350 cells/μl (P = 0.047), as were lower infant height-for-age z-scores (P = 0.016). Supplementation with multivitamins containing B complex, C, and E does not appear to improve measles vaccine responses for HIV-exposed infants. Studies are needed to better characterize the impact of maternal HIV disease severity on the immune system development of HIV-exposed infants and the effect of malnutrition interventions on vaccine responses. (This study has been registered at ClinicalTrials.gov under registration no. NCT00197730.).

Reduced varicella-zoster-virus (VZV)-specific lymphocytes and IgG antibody avidity in solid organ transplant recipients

BACKGROUND

Varicella-zoster-virus (VZV) infection may cause significant morbidity and mortality in immunocompromised patients. So far, only IgG-anti-VZV antibody concentrations were used to estimate immunity against VZV, but the antibody binding strength (avidity) together with VZV-specific cellular responses have not been evaluated in solid organ transplant (SOT) recipients.

METHODS

Thus, we assessed the humoral and cellular immune responses to two doses of the VZV vaccine (vacc) and wild-type VZV infection (wt) in 23 kidney (KTx) and 19 liver transplant (LTx) recipients including children and adults compared to 48 healthy controls (HC) for measurement of IgG-anti-VZV relative avidity index (RAI) and frequency of VZV-specific peripheral blood mononuclear cells (PBMCs) in vaccinated individuals using an adapted ELISA and IFN-gamma ELISPOT, respectively.

RESULTS

KTx(wt) (median RAI 72.3%) or LTx(wt) (79.2%) and KTx(vacc) (91.0%) or LTx(vacc) (72.5%) showed lower avidities compared to HC(wt) (84.5%) and HC(vacc) (94.0%), respectively, despite equally distributed IgG-anti-VZV concentrations. RAI>60% (high avidity) was detected in all HC, but only in 69.0% of SOT patients. KTx(vacc) (median 64 spot forming units SFU/500,000 PBMCs) and LTx(vacc) (67 SFU) had significantly lower VZV-specific cellular responses compared to HC(vacc) (268 SFU).

CONCLUSIONS

The diminished cellular reactivity to VZV has to be considered in SOT patients receiving immunosuppressive treatments when evaluating immunity against VZV. IgG antibody avidity and VZV-specific cellular responses may serve as additional markers to evaluate immunity against VZV in SOT recipients. The role of wild-type exposures and endogenous VZV re-activation on long-term immunity in SOT patients has to be awaited to establish recommendations for vaccine spacing in these patients, considering immunogenicity and safety aspects.

Consequences of immature and senescent immune responses for infection with respiratory syncytial virus

Infants in the first 6 months of life and older adults (>65 years of age) are disproportionately burdened with respiratory syncytial virus (RSV)-associated morbidity and mortality. While other factors play a role in the risk these groups assume, shortcomings of the immune response make a substantial contribution to the predisposition to severe disease. Ineffectual antibody production with misdirected cytokine responses and excess inflammation in the airways are common to both groups. However, the mechanisms underlying these immune responses differ between infants and older adults and need to be better understood. Preventative approaches to decreasing the burden of disease are preferable to therapeutic intervention and effective vaccination strategies will need to target the strengths of the immune responses in these populations.

Differences of IgG antibody avidity after an acellular pertussis (aP) booster in adolescents after a whole cell (wcP) or aP primary vaccination

Compared to whole cell pertussis (wcP) vaccines, acellular pertussis vaccines (aP) have a better safety profile with lower reactogenicity, although their short and long-term efficacy was found to be slightly lower. Up to now, no established serological parameter to predict long-term protection exists. IgG-anti-pertussis avidity possibly determines the effect of different pertussis vaccines and boosting intervals on long-term immunity. Thus, the avidity of a tetanus-diphtheria-aP booster at 10-14 years was tested in three groups of adolescents who had been previously immunized with either five doses of aP (5aP) at 2, 4, 6, 15-18 months and 5-6 years of age, four doses of aP (4aP) or four doses of wcP (4wcP) at 2, 4, 6 and 15-18 months of age. Relative avidity index (RAI) of IgG-anti-pertussis toxin (PT) and IgG-anti-filamentous-hemagglutinin (FHA) was assessed by an adapted ELISA. RAI of IgG-anti-PT and of IgG-anti-FHA correlated positively with antibody concentrations in the pre-vaccination and in the post-vaccination analysis and significantly increased after adolescent booster with aP in all groups. Pre- and post-vaccination, the proportion of participants with IgG-anti-PT RAI>40% (moderate to high avidity) was significantly lower in the 4wcP group (52.9% and 88.9%) compared to the 5aP group (89.5% and 100.0%). In conclusion, TdaP in adolescence induces an increase of antibody avidity and, thus, is able to enhance the binding-quality of antibodies against pertussis. The study suggests including antibody avidity into serological studies on the humoral response to provide information about the long-term efficacy of the vaccine.

Assessment of IgG avidity against pertussis toxin and filamentous hemagglutinin via an adapted enzyme-linked immunosorbent assay (ELISA) using ammonium thiocyanate

Antibody avidity, defined as the strength of binding between antibody and antigen, represents a functional measure of affinity maturation of antibodies. Determination of the antibody avidity is usually performed separating high and low avidity antibodies by dissociating agents, but measurement of the antibody avidity in humans is rather complicated, due to the heterogeneity of the antibodies produced in response to complex antigens, e.g. after vaccinations. The purpose of the present study was to evaluate the experimental determinants of the assessment of avidities of IgG antibodies directed against pertussis toxin (IgG-anti-PT) and filamentous hemagglutinin (IgG-anti-FHA) produced after pertussis vaccination using an adapted ELISA and ammonium thiocyanate (NH(4)SCN) as dissociating agent. Our experiments revealed that the results of avidity testing depend very much on experimental conditions and may over- or underestimate the relative avidity of IgG-anti-PT and IgG-anti-FHA antibodies. Whereas in our findings avidity seems to be independent from the initial antibody concentration in a wide range of measures, RAI depends on NH(4)SCN concentration, time of incubation and temperature of the reaction. The presented method allows an accurate measurement of the IgG antibody avidity against both Bordetella pertussis antigens PT and FHA, using NH(4)SCN as chaotropic agent in concentrations lower than 3.0M for 20 min time of incubation at 37 °C. Different experimental conditions in testing pertussis-specific IgG antibody avidity should be considered in interpretation and comparability of data of different studies.

B-cell responses to vaccination at the extremes of age

Infants and the elderly share a high vulnerability to infections and therefore have specific immunization requirements. Inducing potent and sustained B-cell responses is as challenging in infants as it is in older subjects. Several mechanisms to explain the decreased B-cell responses at the extremes of age apply to both infants and the elderly. These include intrinsic B-cell limitations as well as numerous microenvironmental factors in lymphoid organs and the bone marrow. This Review describes the mechanisms that shape B-cell responses at the extremes of age and how they could be taken into account to design more effective immunization strategies for these high-risk age groups.

The postnatal maturation of the immunoglobulin heavy chain IgG repertoire in human preterm neonates is slower than in term neonates

During the perinatal period the development of the IgH chain CDR3 (CDR-H3) repertoire of IgM transcripts is maturity-dependent and not influenced by premature exposure to Ag. To study whether maturity-dependent restrictions also predominate in the perinatal IgG repertoire we compared 1000 IgG transcripts from cord blood and venous blood of extremely preterm neonates (24-28 wk of gestation) and of term neonates from birth until early infancy with those of adults. We found the following. First, premature contact with the extrauterine environment induced the premature development of an IgG repertoire. However after preterm birth the diversification of the IgG repertoire was slower than that after term birth. Second, the IgG repertoire of preterm neonates retained immature characteristics such as short CDR-H3 regions and overrepresentation of D(H)7-27. Third, despite premature exposure to the extrauterine environment, somatic mutation frequency in IgG transcripts of preterm infants remained low until they reached a postconceptional age corresponding to the end of term gestation. Thereafter, somatic mutations accumulated with age at similar rates in preterm and term neonates and reached 30% of the adult level after 6 mo. In conclusion, class switch was inducible already at the beginning of the third trimester of gestation, but the developing IgG repertoire was characterized by similar restrictions as those of the developing IgM repertoire. Those B cells expressing more "mature" H chain sequences were not preferentially selected into the IgG repertoire. Therefore, the postnatal IgG repertoire of preterm infants until the expected date of delivery differs from the postnatal repertoire of term neonates.

Transcriptional control of activation-induced cytidine deaminase and error-prone DNA polymerases is functionally mature in the B cells of infants at birth

Somatic hypermutation (SHM) of immunoglobulin genes requires activation-induced cytidine deaminase (AID). The error-prone DNA polymerases, such as Pol eta, Pol zeta, and Pol iota, also have been implicated in the process. Human adult antibodies directed to microbial pathogens are increased in affinity and function compared with those of infants. Adult antibodies achieve this increased affinity through somatic mutations, which are lacking in the B cells of infants. It is unknown if infant B cells are capable of upregulating the cell machinery needed to introduce mutations after stimulation through the antigen receptor. We show here that infant B cells exhibit similar kinetics and magnitude of transcription of AID and pol eta genes and only marginally lower levels of pol iota and pol zeta genes after stimulation through the B cell receptor. These data suggest that the ability to upregulate gene transcription of enzymes mediating SHM is not a limiting determinant of the functional quality of infant antibody responses.

Natural evolution of a human virus-specific antibody gene repertoire by somatic hypermutation requires both hotspot-directed and randomly-directed processes

Somatic hypermutation of antibody genes is mediated by activation-induced cytidine deaminase and targets primarily hotspot motifs. We tested the hypothesis that the antibody variable genes of virus-specific B cells from infants exhibit a decreased frequency of somatic mutations compared with adults. We also sought to determine whether virus-specific B cells exhibit predominantly hotspot or randomly directed processes. We analyzed somatic mutations in rotavirus (RV)-specific B cells from otherwise healthy but recently RV-infected infants or adults in comparison with B cells from healthy volunteers not recently infected. We compared these antibody variable gene sequences with those derived from RV-specific B cells from an adult patient with X-linked hyper-IgM syndrome (XHIM). We found that the overall mutational frequency within the antibody variable region was lowest in RV-specific B cells from RV-infected infants, followed by randomly selected B cells, followed by RV-specific B cells from the patient with XHIM. RV-specific memory B cells from healthy adults exhibited the highest frequency of mutations. Approximately half of mutations in random or RV-specific B cells from adults or infants occurred at the DGYW/WRCH or WA/TW hotspot motifs. These findings suggest that virus-specific antibodies require both hotspot and randomly-directed processes.

The advantage of mucosal immunization for polysaccharide-specific memory responses in early life

The aim of vaccination is to rapidly elicit protective immunity and generate memory for sustained protection. We studied the induction and persistence of polysaccharide (PS)-specific memory in neonatal and infant mice primed with pneumococcal conjugate (Pnc1-TT) by assessing the response to native pneumococcal PS (PPS-1), the kinetics of the PPS-1-specific IgG response to a second Pnc1-TT dose and affinity maturation. A subcutaneous (s.c.) Pnc1-TT booster induced a rapid increase in PPS-1-specific IgG, indicating efficient priming for memory by a single dose of Pnc1-TT already at 1 week of age. High levels were maintained for >12 weeks. However, a PPS-1 booster induced no response in neonatal or infant mice. The adjuvant LT-K63 significantly enhanced the IgG response and affinity to Pnc1-TT by both the s.c. and the intranasal (i.n.) route in all age groups. In neonatal and infant mice, PPS-1 and LT-K63 induced a booster response only when given i.n. following either s.c. or i.n. priming with Pnc1-TT and LT-K63. In contrast, PPS-1 with or without LT-K63 administered s.c. compromised the ongoing PPS-1-specific response elicited in neonatal mice by either s.c. or i.n. priming with Pnc1-TT and LT-K63. These results demonstrate the advantage of the mucosal route for elicitation of PS-specific memory responses in early life.

Functional responses of human neonatal B lymphocytes to antigen receptor cross-linking and CpG DNA

Human neonates are immunologically immature and consequently are highly susceptible to infection. The cellular basis for the dysfunctional immune responses of neonates is not clear, but is likely to reflect the immaturity of both B and T cell populations. Here we have examined the ability of human cord blood B cells to respond to antigen receptor cross-linking and also to CpG containing oligodeoxynucleotides (ODN), and compared their responses with those of adult peripheral blood B cells. Antigen receptor cross-linking with soluble F(ab')2 anti-IgM antibodies, induced HLA-DR and CD86 up-regulation and proliferation to a similar extent in adult and cord blood B cells. Both interleukin (IL)-2 and IL-4 co-stimulated anti-IgM-induced proliferation, but cord blood B cells were less sensitive than adult B cells to the co-stimulatory effects of IL-2. Antigen receptor cross-linking induced secretion of the chemokines macrophage inflammatory protein-1 alpha (MIP-1 alpha) and MIP-1 beta in adult and cord blood B cells, and secretion was enhanced by IL-2 or IL-4. CpG-ODN induced up-regulation of HLA-DR and CD86 expression and proliferation of adult and cord blood B cells, and anti-IgM and CPG-ODN synergized in the induction of proliferation. CpG-ODN also induced MIP-1 alpha and MIP-1 alpha secretion in adult and cord blood B cells. In addition to functional studies we examined the expression of CD62L (l-selectin), CCR7 and CXCR5. Our data show that surface expression of CD62L and CCR7 is lower on cord blood B cells than on adult B cells, suggesting that human cord blood B cells may exhibit homing defects.

Isolation of antigen-specific B cells

Cell separation techniques are important in immunology. Major cell populations can be separated successfully with high purity. However, isolation of cells which are specific for particular antigens is more challenging because of the relatively small numbers of antigen-specific cells, and the lack of independent markers available to determine the purity of the isolated population. In this review, the literature describing three principal techniques used to separate antigen-specific cells has been reviewed. Particular emphasis has been placed on yield and purity; the two most important parameters of any purification method. The most promising isolation methods have used immunomagnetic sorting and multiparametric flow cytometric analysis.

Neonatal and early life vaccinology

Preclinical and human vaccine studies indicate that, although neonatal immunisation does not generally lead to rapid and strong antibody responses, it may result in an efficient immunological priming, which can serve as an excellent basis for future responses. The apparent impairment of CD4 and CD8 T-cell function in early life seems to result from suboptimal antigen-presenting cells-T cell interactions, which can be overcome by use of specific adjuvants or delivery systems. Although persistence of maternal antibodies may limit infant antibody responses, induction of T-cell responses largely remain unaffected by these passively transferred antibodies. Thus, neonatal priming and early boosting with vaccine formulations optimised for sufficient early life immunogenicity and maximal safety profiles, could allow better control of the huge infectious disease burden in early life.

The Fc receptor for IgG (Fc gamma RII; CD32) on human neonatal B lymphocytes

B cells express an Fc receptor for IgG (FcgammaRII; CD32) which is involved in feedback inhibition of antibody production. Engagement of FcgammaRII during ligation of the antigen receptor provides an inhibitory signal. FcgammaRII exists as several isoforms, with FcgammaRIIb (which carries an immunoreceptor tyrosine-based inhibition motif; ITIM) being predominant form on adult B cells. The inhibitory role of FcgammaRIIb may be unhelpful to the infant, since primary exposure to infectious agents is likely to be in the presence of maternal IgG. We hypothesized that neonatal B cells would be less susceptible to feedback inhibition by antibody, either through the expression of activation-competent FcgammaRII isoforms (FcgammaRIIa and FcgammaRIIc) or through reduced expression of the inhibitory FcgammaRIIb isoforms. Cord and adult B cells were examined for expression of FcgammaRII isoforms using monoclonal antibodies and RT-PCR. In vitro assays were performed to assess susceptibility of cord and adult cells to FcgammaRII-mediated suppression. Although there is no phenotypic difference in FcgammaRII expression (FcgammaRIIb predominating on both adult and cord B cells), FcgammaRIIb is expressed at lower levels on cord cells. This quantitative difference in FcgammaRIIb expression may explain the reduced susceptibility of cord B cells to antibody-mediated inhibition observed in these experiments.

Vaccination in the neonatal period and early infancy

Immune maturation is responsible for a progressive increase in antibody responses that can be elicited during the first year of life, such that neonatal immunization may currently not be expected to induce strong antibody responses. In contrast, B and T cell priming can be induced very early in life, without interference of maternal immunity. Strong IL-5 and IL-13 responses in young mice, and limited IL-12 and IFN-gamma release capacity by early life APC and T cells both in young mice and infants, could contribute to the severity of infections with intracellular pathogens in early life. It calls for evaluation of novel delivery systems, adjuvants and/or prime-boost immunization strategies capable to meet the challenge of both strong neonatal immunogenicity and acceptable reactogenicity. The extent to which early life murine immunization models may be useful for preclinical evaluation of infant responses is outlined in this review.

Neonatal immunity and somatic mutation

Neonatal animals are able to mount an effective immune response, both humoral and cellular, when immunized using conditions that maximize stimulation of antigen presenting cells, T cells, and B cells. In adults, somatic mutation is a key feature of the humoral immune response because it contributes to the generation of high affinity memory B cells. Recent evidence that B cells in neonatal mice and human infants can somatically mutate their immunoglobulin heavy chains suggests that neonates can utilize somatic mutation not only to diversify their restricted germline antibody repertoire, but also to improve upon this repertoire by the generation of B cells which can produce higher affinity antibodies. By extrapolation, if vaccination of children early in life resulted in somatic mutation and affinity maturation, this could provide a more protective antibody response to childhood diseases.