Neonatal immunology

Absence of Epstein-Barr virus in smooth muscle cells of idiopathic hypertrophic pyloric stenosis

CONTEXT

The etiology of idiopathic hypertrophic pyloric stenosis (IHPS) is unknown. Epstein-Barr virus (EBV) infects smooth muscle cells and is associated with leiomyomas and leiomyosarcomas of immunocompromised persons, including persons with the acquired immunodeficiency syndrome.

OBJECTIVE

To determine whether EBV is causally associated with IHPS.

DESIGN

Biopsy samples of the pylorus were obtained from 10 infants with projectile vomiting and pyloric hypertrophy on ultrasound, with confirmation of hypertrophy at the time of pyloromyotomy. The presence of EBV infection was tested by in situ hybridization for EBV-encoded RNA 1 (EBER1) in smooth muscle cells of IHPS.

SETTING

Biopsy specimens were obtained from children treated for IHPS at a tertiary referral hospital and were tested in a clinical molecular diagnostics laboratory.

RESULTS

All of the 10 smooth muscle biopsies were negative for EBER1. Cellular U6 RNA was detected in all smooth muscle samples, confirming that the RNA in the specimens was intact and capable of detection by in situ hybridization.

CONCLUSIONS

The absence of EBER1 in 10 cases of clinically diagnosed and histopathologically confirmed cases of IHPS effectively excludes EBV infection of smooth muscle cells as a causal factor in the pathogenesis of IHPS.

Th1 genetic adjuvants modulate immune responses in neonates

In these studies, we address the ability of DNA encoding Th1 cytokines to bias the isotype of antibody raised by neonatal or adult immunization with an influenza hemagglutinin expressing DNA (HA-DNA). Neonatal mice coimmunized with HA-DNA and either IL-12 or IFN-gamma-expressing DNA developed IgG2a-biased immune responses, regardless of inoculation method. In contrast, the Th1 genetic adjuvants had no effect on IgG subtype patterns in adults. In neonatal mice, the Th1 genetic adjuvants also shifted the pattern of lymphokine production by recall splenocytes from a mixed response of IFN-gamma and IL-5 to exclusively IFN-gamma. In adults, despite the failure to change the isotype pattern of the antibody response, a shift towards IFN-gamma production also occurred for recall splenocytes following coimmunzation with IL-12. Thus, coinoculation of Th1 genetic adjuvants had greater effects on the nature of the immune response in the neonate than in adults.

Neonatal (cord blood) T cells can competently raise type 1 and 2 immune responses upon polyclonal activation

In the neonate, cellular immunity has generally been hypothesized as being incompetent. Accumulating evidence from several recent studies, together with our present report, contradicts this hypothesis. T-helper cell and T cytotoxic type 1 and 2 (Th1/Th2 and Tc1/Tc2, respectively) cytokine responses to polyclonal T cell receptor (TCR) activation were assessed in medium-term cultures of human cord blood T cells using intracellular cytokine staining, which could measure the frequencies of cytokine-producing cells. In this study, we examined the responses of cord blood CD4(+) and CD8(+) T cells in regard to the production of interferon (IFN)-gamma and interleukin (IL)-4 and compared the responses with those obtained from T cells of healthy adults. We found that the responses in cord blood T cells activated with TCR stimulation were comparable to those of their adult counterparts. Moreover, the Th/Tc cells that developed in cord blood were as competent as adult cells for both IFN-gamma and IL-4 secretion. In addition, IL-12 production, which is critical for both Th1 and Tc1 responses, was equally comparable in the two groups. The production of two major cross-regulatory cytokines, tumor necrosis factor-alpha and IL-10, was similarly comparable and not significantly different between the two groups. Taken together, these results indicate that, though naive, the neonatal T cell is competent to respond to TCR-mediated stimulation and to produce both type 1 and type 2 cytokines.

Enhancement of neonatal innate defense: effects of adding an N-terminal recombinant fragment of bactericidal/permeability-increasing protein on growth and tumor necrosis factor-inducing activity of gram-negative bacteria tested in neonatal cord blood ex vivo

Innate defense against microbial infection requires the action of neutrophils, which have cytoplasmic granules replete with antibiotic proteins and peptides. Bactericidal/permeability-increasing protein (BPI) is found in the primary granules of adult neutrophils, has a high affinity for lipopolysaccharides (or "endotoxins"), and exerts selective cytotoxic, antiendotoxic, and opsonic activity against gram-negative bacteria. We have previously reported that neutrophils derived from newborn cord blood are deficient in BPI (O. Levy et al., Pediatrics 104:1327-1333, 1999). The relative deficiency in BPI of newborns raised the possibility that supplementing the levels of BPI in plasma might enhance newborn antibacterial defense. Here we determined the effects of addition of recombinant 21-kDa N-terminal BPI fragment (rBPI(21)) on the growth and tumor necrosis factor (TNF)-inducing activity of representative gram-negative clinical isolates. Bacteria were tested in citrated newborn cord blood or adult peripheral blood. Bacterial viability was assessed by plating assay, and TNF-alpha release was measured by enzyme-linked immunosorbent assay. Whereas adult blood limited the growth of all isolates except Klebsiella pneumoniae, cord blood also allowed logarithmic growth of Escherichia coli K1/r and Citrobacter koseri. Bacteria varied in their susceptibility to rBPI(21)'s bactericidal action: E. coli K1/r was relatively susceptible (50% inhibitory concentration [IC(50)], approximately 10 nM), C. koseri was intermediate (IC(50), approximately 1,000 nM), Klebsiella pneumoniae was resistant (IC(50), approximately 10,000 nM), and Enterobacter cloacae and Serratia marcescens were highly resistant (IC(50), >10,000 nM). All isolates were potent inducers of TNF-alpha activity in both adult and newborn cord blood. In contrast to its variable antibacterial activity, rBPI(21) consistently inhibited the TNF-inducing activity of all strains tested (IC(50), 1 to 1,000 nM). The antibacterial effects of rBPI(21) were additive with those of a combination of conventional antibiotics typically used to treat bacteremic newborns (ampicillin and gentamicin). Whereas ampicillin and gentamicin demonstrated little inhibition of bacterially induced TNF release, addition of rBPI(21) either alone or together with ampicillin and gentamicin profoundly inhibited release of this cytokine. Thus, supplementing newborn cord blood with rBPI(21) potently inhibited the TNF-inducing activity of a variety of gram-negative bacterial clinical pathogens and, in some cases, enhanced bactericidal activity. These results suggest that administration of rBPI(21) may be of clinical benefit to neonates suffering from gram-negative bacterial infection and/or endotoxemia.

Analysis of the human neonatal thymus: evidence for a transient thymic involution

The neonatal period is marked by the impairment of the major components of both innate and adaptive immunity. We report a severe depletion of cortical CD4+CD8+ double-positive thymocytes in the human neonatal thymus. This drastic reduction in immature double-positive cells, largely provoked by an increased rate of cell death, could be observed as early as 1 day after birth, delaying the recovery of the normal proportion of this thymocyte subset until the end of the first month of postnatal life. Serum cortisol levels were not increased in newborn donors, indicating that the neonatal thymic involution is a physiological rather than a stress-associated pathological event occurring in the perinatal period. Newborn thymuses also showed increased proportions of both primitive CD34+CD1- precursor cells and mature TCRalphabetahighCD69-CD1-CD45RO+/RAdull and CD45ROdull/RA+ cells, which presumably correspond to recirculating T lymphocytes into the thymus. A notable reinforcement of the subcapsular epithelial cell layer as well as an increase in the intralobular extracellular matrix network accompanied modifications in the thymocyte population. Additionally neonatal thymic dendritic cells were found to be more effective than dendritic cells isolated from children's thymuses at stimulating proliferative responses in allogeneic T cells. All these findings can account for several alterations affecting the peripheral pool of T lymphocytes in the perinatal period.

Immunosuppression for pediatric cardiac transplantation in the modern era

With the advent of the T cell activation inhibitors such as cyclosporine, heart transplant success rates for pediatric patients have improved to the point that the initially restricted ages and indications have expanded considerably. Currently the half-life (50% still alive) for children transplanted in the early 1980s is approximately 12-14 years. Decades-long survival seems likely. Components and functions of the immune system are naïve and change during postnatal development. Maturation occurs not only in the first years of life, but well through adolescence and even into adult life. These age-dependent changes within the immune system greatly complicate any attempt to assess immune implications for the use of immunosuppression in children. Since the introduction of cyclosporine, immunosuppression regimens have been virtually unchanged through the 1990s. Recently, there have been significant new immune pharmacological agents which are now commercially available, or still in investigational stages of development. The new maintenance immunosuppressive drugs are either inhibitors of de novo synthesis of nucleotides (purines or pyrimidines), or are immunophilin-binding drugs that inhibit signal transduction in lymphocytes. The newer inhibitors of de novo nucleotide synthesis include mycophenolate mofetil, mizoribine, brequinar and leflunomide. The immunophilin-binding drugs are cyclosporine, tacrolimus and rapamycin. Antibody preparations such as ATG, ATGAM and OKT3, as well as the newer biological agents, which specifically bind to the IL-2 receptor, basiliximab and daclizumab, are discussed. The potential for biologicals which inhibit co-stimulation are also discussed. There may be dramatic changes in protocols used clinically as a result of these new agents over the next decade. The increasing understanding of the alloimmune response as well as the clinical use of these newer drugs promise even better long-term results.

Impaired innate immunity in the newborn: newborn neutrophils are deficient in bactericidal/permeability-increasing protein

OBJECTIVE

The mechanisms by which newborns are at increased risk for invasive bacterial infections have been incompletely defined. A central element of innate immunity to bacterial infection is the neutrophil-a cell that contains cytoplasmic granules replete with antibiotic proteins and peptides. The activity of adult neutrophils against gram-negative bacteria is believed to depend to a significant degree on the presence in neutrophil primary (azurophilic) granules of the 55-kDa bactericidal/permeability-increasing protein (BPI), which binds with high affinity to bacterial lipopolysaccharides and kills gram-negative bacteria. In light of the importance of BPI to antibacterial host defense and to investigate possible factors underlying the risk of neonatal bacterial infections, we determined the relative content of BPI in the neutrophils of adults and newborns.

DESIGN

The cellular content of BPI was determined by Western blotting of neutrophils derived from full-term newborn cord blood (n = 21; mean gestational age: 38.6 weeks) and from adult peripheral blood (n = 22; mean age: 29 years). Extracellular levels of BPI in adult and newborn plasma were assessed by enzyme-linked immunosorbent assay. Neutrophil content of other azurophil granule markers also was assessed: myeloperoxidase by Western blotting and defensin peptides by acid-urea polyacrylamide gel electrophoresis and Coomassie staining. Acid extracts of newborn and adult neutrophils were analyzed for antibacterial activity against serum-resistant encapsulated isolate Escherichia coli K1/r.

RESULTS

The neutrophils of newborns contain at least threefold to fourfold less BPI per cell than adult neutrophils (67 +/- 13 ng per 10(6) cells vs 234 +/- 27 ng per 10(6) cells). The relative BPI-deficiency of newborn neutrophils apparently was not attributable to perinatal stress-related degranulation of intracellular BPI stores because: 1) newborn and adult neutrophils contained nearly identical amounts of 2 microbicidal constituents derived from the same primary (azurophil) granule compartment as BPI (the enzyme myeloperoxidase as well as defensin peptides), and 2) levels of extracellular BPI in newborn plasma, measured by enzyme-linked immunosorbent assay, represent only approximately 2% of cellular BPI content. As predicted by their lower BPI content, newborn neutrophil acid extracts demonstrated significantly lower antibacterial activity against E coli K1/r than did adult neutrophil acid extracts.

CONCLUSION

These data suggest that the neutrophils of newborns are selectively deficient in BPI, a central effector of antibacterial activity against gram-negative bacteria. BPI deficiency correlates with decreased antibacterial activity of newborn neutrophil extracts against serum-resistant E coli and could contribute to the increased incidence of gram-negative sepsis among newborns relative to healthy adults.neonatal sepsis, gram-negative bacteria, endotoxin, neutrophil, polymorphonuclear leukocyte, innate immunity, bactericidal/permeability-increasing protein, defensin, myeloperoxidase.

Bacterial meningitis and the newborn infant

Bacterial meningitis in the neonate differs from meningitis in the older infant and child in a number of ways. Bacterial pathogens primarily are associated with the maternal genitourinary tract. Symptoms and physical findings may be nonspecific, and a high index of suspicion is needed. Management may vary depending on the maturity of the infant and the bacterial pathogen that is isolated.

Studies on antibody responses following neonatal immunization with influenza hemagglutinin DNA or protein

Neonatal mice have immature immune systems with defects in several components of inflammatory, innate, and specific immune responses and develop a preferential T helper type 2 response following immunization with many vaccine antigens. These studies were undertaken to determine whether 1-day-old neonatal mice immunized with plasmid DNA expressing influenza A/PR/8/34 hemagglutinin (H1) by either intramuscular (im) or gene gun (gg) inoculation were capable of generating humoral responses comparable to those in mice immunized as adults. The newborn mice developed stable, long-lived, protective anti-H1-specific IgG responses similar in titer to those of adult DNA-immunized mice. However, unlike the adult im and gg DNA immunizations, which develop polarized IgG2a and IgG1 responses, respectively, mice immunized as neonates developed a variety of IgG1, IgG2a, and mixed IgG1/IgG2a responses regardless of the inoculation method. Boosting increased but did not change these antibody profiles. In contrast to the DNA immunizations, inoculations of newborn mice with an A/PR/8/34 viral protein subunit preparation failed to elicit an antibody response. Temporal studies revealed that both responsiveness to protein vaccination and development of polarized patterns of T help following DNA immunization appeared by 2 weeks of age.