Characterization of early activation events in cord blood B cells after stimulation with T cell-independent activators

Vaccines against respiratory viral pathogens for use in neonates: opportunities and challenges

The first six months of life reflect a time of high susceptibility to severe disease following respiratory virus infection. Although this could be improved significantly by immunization, current vaccines are not approved for use in these very young individuals. This is the result of the combined effects of poor immune responsiveness and safety concerns regarding the use of live attenuated vaccines or potent adjuvants in this population. Vaccines to effectively combat respiratory viral infection ideally would result in robust CD4(+) and CD8(+) T cell responses, as well as high-affinity Ab. Inclusion of TLR agonists or single-cycle viruses is an attractive approach for provision of signals that can act as potent stimulators of dendritic cell maturation, as well as direct activators of T and/or B cells. In this article, I discuss the challenges associated with generation of a robust immune response in neonates and the potential for adjuvants to overcome these obstacles.

DNA immunization against respiratory syncytial virus (RSV) in infant rhesus monkeys

A DNA vaccine was tested in infant Rhesus macaques to evaluate its safety, immunogenicity and protective efficacy. Monkeys were vaccinated and challenged with a clinical isolate of human RSV. Vaccinated animals developed humoral and cellular responses following inoculation with plasmid DNA encoding the fusion (F) and nucleoprotein (N), from closely related bovine RSV. Vaccinated monkeys had decreased RSV in their lungs post-infection, and there was a qualitative difference in histopathology observed between vaccinated and unvaccinated animals. The combined result of safety and immunogenicity in a neonatal primate model is encouraging, suggesting the feasibility of DNA vaccines against RSV in infants.

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.

Congenital exposure to Plasmodium falciparum antigens: prevalence and antigenic specificity of in utero-produced antimalarial immunoglobulin M antibodies

Congenital Plasmodium falciparum malaria in newborns is uncommon in sub-Saharan Africa. A significant number of infants, however, become infected or exposed to malarial antigens either in utero or at delivery and have the potential to produce antimalarial antibodies and memory cells before their first natural infection. In Yaounde, Cameroon, parasite-specific immunoglobulin M (IgM) was detected in 14% of cord blood samples. The IgM antibodies reacted with a wide range of asexual-stage antigens, with each newborn having its own unique pattern of IgM reactivity. PCR-based detection and genotyping of cord blood parasites found that the prevalence, total number of parasite genotypes, and complexity of infection were higher in newborns who had produced antimalarial IgM than those who had not. Maternal placental malaria and anemia were associated with the production of P. falciparum-specific IgM by the fetus. The effect of early immune priming on acquisition of immunity by infants is unknown and merits further investigation, since a significant proportion of Cameroonian newborns developed a humoral response to malaria before birth.

Hyperoxia- and hypoxia-mediated activation of polymorphonuclear leukocytes: a comparison of cord and adult venous blood

BACKGROUND

Among the most prominent changes occurring in newborn infants is the exposure of tissues and blood cells to increased oxygen tension. This increase is even more pronounced in neonatal resuscitation using 100% oxygen, currently recommended in the published guidelines.

OBJECTIVE

To analyse the response of neonatal and adult polymorphonuclear neutrophils (PMN) to high or low oxygen tension in vitro.

MATERIALS

Neonatal cord blood and adult venous blood without previous contact to ambient air was exposed to 0, 21, or 100% oxygen for 30 min followed by incubation for up to 24 h.

METHODS

Flow cytometry was used to assess PMN activation as indicated by downregulation of L-selectin expression. Cell viability was quantified by the amount of propidium iodide uptake.

RESULTS

In adult PMN, L-selectin downregulation was greatly accelerated by hypoxia (PO2=27.2+/-3.4 mmHg) compared with both normoxia (PO2=71.0+/-11.0 mmHg) or hyperoxia (PO2=653.2+/-9.4) (P<0.05). In contrast, hyperoxia was the most potent stimulus for cord blood PMN, compared with both normoxia and hypoxia (P<0.05). Evidence of necrosis as indicated by positive staining for propidium iodide was similar in cord blood (10 h: 5.83% in oxygen) and in adult blood (10 h: 6.45% in oxygen). No differences were found between exposure to hypoxia, normoxia, or hyperoxia.

CONCLUSION

Oxygen exposure of neonatal PMN leads to a more pronounced activation as compared with adult cells. Exposure towards high concentrations of oxygen may contribute to inflammatory processes during early neonatal life.

Adjuvant effects of CpG oligodeoxynucleotides on responses against T-independent type 2 antigens

Oligodeoxynucleotides containing CpG motifs (CpG-ODN) are potent in vitro B-cell activators and they have been successfully used to increase in vivo antibody responses to T-dependent peptide and protein antigens. In contrast, the use of CpG-ODN to enhance in vivo antibody responses to various T-independent type 2 (TI-2) antigens has recently generated contradictory results. In this study, we compared the CpG-ODN stimulatory effect on antibody responses of adult and young BALB/c mice to trinitrophenylaminoethyl-carboxymethyl (TNP) -Ficoll and to polysaccharides (PS) from several distinct serotypes of Streptococcus pneumoniae (SPn). CpG-ODN co-administration significantly enhanced antigen-specific immunoglobulin M (IgM), IgG, IgG1 and IgG2a titres to TNP-Ficoll. The depletion of CD4+ cells by monoclonal antibodies (GK1.5) identified their essential role in CpG-ODN-mediated enhancement of antibody responses. In contrast to TNP-Ficoll, CpG-ODN failed to enhance IgM and IgG responses to any of the 18 SPnPS serotypes tested. Providing T-cell epitopes by the conjugation of SPnPS to the carrier protein tetanus toxoid again allowed CpG-ODN to mediate enhancement of IgG, IgG2a and IgG3 responses to most SPnPS serotypes. Thus, antigen-presenting cell/T-cell interaction appears to largely mediate the in vivo influence of CpG-ODN on antibody responses to TI-2 antigens. In early life, additional factors limit CpG-ODN modulation of antibody responses to TI-2 antigens.