Effect of Breast Feeding on Immunologic Priming in Young Infants

The mechanisms generating immunoglobulin heavy chain (IgH) biodiversity result in over potentially unique immunoglobulin sequences within an individual. However, over the course of B cell development, B cell receptor (BCR) selection constrains the repertoire significantly. In newborn infants compared to adults, developmental regulation of terminal deoxynucleotidyl transferase (TdT) activity in the bone marrow, selective use of V, D and J gene segments in the IgH locus during fetal life, and immaturity of somatic hypermutation (SHM) and class switch recombination (CSR) mechanisms are likely to contribute to a less diverse IgH repertoire, although the extent of repertoire biodiversity in newborns has not been extensively examined. Furthermore, the fetal IgH repertoire is tightly controlled and for the most part independent of environmental antigenic influences. As a result, the neonatal repertoire, in contrast to older children and adults, is less impacted by the selective pressures of the microbiome, pathogen exposure, and environmental antigens. Evidence for developmental differences in TdT activity is seen in shorter CDR3 lengths and decreased junctional diversity in BCR in both term and preterm newborns. Next Generation Sequencing (NGS) is a sensitive approach to evaluate the neonatal IgH repertoire and assess the relative contribution of each aspect of IgH rearrangement and affinity maturation to overall IgH biodiversity prior to and following isotype class switch. NGS and bioinformatics accurately assess biodiversity by determining the number of unique sequences within the IgH repertoire. Combined with novel analytic tools, NGS provides an approach to compare the extent of somatic hypermutation (SHM), N insertions, V/D/J gene segment usage, and CDR3 length between newborns and adults. Taken together, these measures can be used to assess the earliest events in B cell development using the newborn Ig transcriptome to evaluate the IgM, IgG, and IgA IgH repertoires. The goal of this study was to define the extent of IgH biodiversity in newborns and examine the factors that contribute to the generation of biodiversity during early life. Establishment of the bioinformatics pipeline can be applied to examine the immune deficiency, response to vaccine and infection at molecular population level.]]>
Infant normal control group criteria: Infants without a medical diagnosis who have received all of the recommended American Academy of Pediatrics Vaccinations for age. Adult normal control group criteria: Adults from 17-23 years of age who are without medical diagnoses.]]>
Case and control were sequenced in the year 2019.]]>

产生免疫球蛋白重链（immunoglobulin heavy chain, IgH）多样性的机制，可在个体内产生大量潜在独特的免疫球蛋白序列。然而在B细胞发育过程中，B细胞受体（B cell receptor, BCR）的选择作用会显著限制免疫组库（immune repertoire）的规模。与成人相比，新生儿骨髓中末端脱氧核苷酸转移酶（terminal deoxynucleotidyl transferase, TdT）活性的发育调控、胎儿期IgH位点上V、D、J基因片段的选择性使用，以及体细胞超突变（somatic hypermutation, SHM）与类别转换重组（class switch recombination, CSR）机制的未成熟性，均可能导致IgH免疫组库的多样性水平更低——尽管目前尚未对新生儿免疫组库的多样性程度开展广泛研究。此外，胎儿IgH免疫组库受到严格调控，且在绝大多数情况下不受环境抗原的影响。因此，与年长儿童及成人相比，新生儿免疫组库受微生物组、病原体暴露及环境抗原带来的选择压力影响更小。
有关TdT活性发育差异的证据，可在足月儿与早产儿的BCR中观察到：其CDR3（complementarity determining region 3, CDR3）长度更短，连接多样性降低。下一代测序（Next Generation Sequencing, NGS）是评估新生儿IgH免疫组库的敏感手段，可用于解析IgH重排与亲和力成熟的各个环节在同种型类别转换前后对整体IgH多样性的相对贡献。NGS联合生物信息学（bioinformatics）技术，通过测定IgH免疫组库内的独特序列数量，可精准评估多样性水平。结合新型分析工具，NGS可用于比较新生儿与成人之间的SHM水平、N插入情况、V/D/J基因片段使用偏好及CDR3长度。综上，上述指标可借助新生儿Ig转录组，评估B细胞发育的早期事件，进而检测IgM、IgG及IgA型IgH免疫组库。
本研究旨在明确新生儿的IgH多样性程度，并探究生命早期参与多样性产生的相关影响因素。本研究建立的生物信息学流程，可应用于在分子群体水平上评估免疫缺陷、疫苗应答与感染应答。
婴儿正常对照组标准：完成美国儿科学会（American Academy of Pediatrics, AAP）推荐的适龄疫苗全程接种、无医学诊断的婴儿。
成人正常对照组标准：年龄17~23岁、无医学诊断的成人。
病例组与对照组的测序工作于2019年完成。