Delineation of producing ability of IgG and IgA subclasses by naive B cells in newborn infants and adult individuals

Role of DNA repair in host immune response and inflammation

In recent years, the understanding of how DNA repair contributes to the development of innate and acquired immunity has emerged. The DNA damage incurred during the inflammatory response triggers the activation of DNA repair pathways, which are required for host-cell survival. Here, we reviewed current understanding of the mechanism by which DNA repair contributes to protection against the oxidized DNA damage generated during infectious and inflammatory diseases and its involvement in innate and adaptive immunity. We discussed the functional role of DNA repair enzymes in the immune activation and the relevance of these processes to: transcriptional regulation of cytokines and other genes involved in the inflammatory response; V(D)J recombination; class-switch recombination (CSR); and somatic hypermutation (SHM). These three last processes of DNA damage repair are required for effective humoral adaptive immunity, creating genetic diversity in developing T and B cells. Furthermore, viral replication is also dependent on host DNA repair mechanisms. Therefore, the elucidation of the pathways of DNA damage and its repair that activate innate and adaptive immunity will be important for a better understanding of the immune and inflammatory disorders and developing new therapeutic interventions for treatment of these diseases and for improving their outcome.

SNPs in DNA repair genes associated to meningitis and host immune response

In vitro and in animal models, APE1, OGG1, and PARP-1 have been proposed as being involved with inflammatory response. In this work, we have investigated if the SNPs APE1 Asn148Glu, OGG1 Ser326Cys, and PARP-1 Val762Ala are associated to meningitis. The patient genotypes were investigated by PIRA-PCR or PCR-RFLP. DNA damages were detected in genomic DNA by Fpg treatment. IgG and IgA were measured from plasma and the cytokines and chemokines were measured from cerebrospinal fluid samples using Bio-Plex assays. A higher frequency (P<0.05) of APE1 Glu allele in bacterial meningitis (BM) and aseptic meningitis (AM) patients was observed. The genotypes Asn/Asn in control group and Asn/Glu in BM group was also higher. For the SNP OGG1 Ser326Cys, the genotype Cys/Cys was more frequent (P<0.05) in BM group. The frequency of PARP-1 Val/Val genotype was higher in control group (P<0.05). The occurrence of combined SNPs is significantly higher in BM patients, indicating that these SNPs may be associated to the disease. Increasing in sensitive sites to Fpg was observed in carriers of APE1 Glu allele or OGG1 Cys allele, suggesting that SNPs affect DNA repair activity. Alterations in IgG production were observed in the presence of SNPs APE1 Asn148Glu, OGG1 Ser326Cys or PARP-1 Val762Ala. Moreover, reduction in the levels of IL-6, IL-1Ra, MCP-1/CCL2 and IL-8/CXCL8 was observed in the presence of APE1 Glu allele in BM patients. In conclusion, we obtained indications of an effect of SNPs in DNA repair genes on the regulation of immune response in meningitis.

Age-dependent increase of IgE-binding and FcepsilonRI expression on circulating basophils in children

Peripheral blood basophils are sparse in the circulation, but they express high-affinity receptors for IgE (FCepsilonRI) and bind IgE efficiently. The present study was performed to elucidate the role of IgE bound on the basophil surface in the development of allergic responses during infancy and early childhood. IgE-binding and FcepsilonRI expression on basophils were evaluated by two-color flow cytometry. Basophil-bound IgE increased rapidly and reached adult levels during infancy in atopic patients, while it gradually increased with advancing age in parallel with serum IgE in normal controls. IgE-binding and FcepsilonRI expression in atopic children were higher than in normal controls among various age groups. They correlated with serum IgE levels but reached a plateau when serum IgE exceeded 300 ng/mL. A low, but significant level of FcepsilonRI expression was observed on cord blood basophils, although IgE-binding was usually undetectable. Incubation of cord blood with IgE rapidly saturated the preexisting IgE receptors and basophil-bound IgE levels increased. When neonatal basophils were cultured for 48 h with IgE, FcepsilonRI expression was upregulated dose-dependently and IgE-binding increased further. The up-regulation of FcepsilonRI was completely inhibited by cycloheximide, indicating that it was dependent on de novo protein synthesis. These results suggest that IgE-binding on basophils serves as a sensitive indicator of allergic sensitization, and that IgE functions as a positive regulator of FcepsilonRI expression in vivo.

Neonatal immunology

The neonate, whether premature or of normal gestational age, is a unique host from an immunologic perspective. Many components of the immune system function less well in neonates compared with adults, giving rise to the concept of an "immunodeficiency of immaturity." The adaptive significance of these alterations for neonatal survival remains obscure. This review highlights some of the most prominent quantitative and qualitative differences between neonatal and adult immune systems. From a clinical standpoint, the most important differences appear to be (1) reduction in the available bone marrow reserve of granulocyte precursors, (2) reduction in serum complement activity, (3) decreased ability to produce antibodies against bacterial polysaccharide antigens, and (4) increased percentage of T lymphocytes bearing an antigenically "naive" cell surface phenotype and a correspondingly naive functional program.

The antigen receptor complex on cord B lymphocytes

The neonatal immune system responds to a restricted range of antigens, producing largely IgM antibody of low affinity. Comparison of the components of the B-cell antigen receptor complex shows significantly elevated membrane levels of IgM in neonatal B cells, compared with adult cells. CD79, which acts as the signal transducer for membrane immunoglobulin, is elevated in parallel with IgM, while IgD is elevated to a lesser degree. CD19, CD21, CD22 and CD81, which are all involved in transmitting activation signals when immunoglobulin is engaged, are not elevated. CD32, which is involved in negative regulation of activation, is present at reduced levels on cord B cells. The elevation of B-cell membrane IgM persists during infancy. Neonatal B cells respond in vitro to interleukin-4 (IL-4) by further elevation of membrane IgM levels. The elevated level of membrane IgM may make neonatal B cells easier to trigger by low concentrations of antigen, but in vitro activation and immunoglobulin modulation experiments did not show significant differences between cord and adult B-cell responses to anti-IgM.