Delineation of the functional capacity of human neonatal lymphocytes

Mucosal and systemic immune responses to Aujeszky's disease virus (ADV) in early vaccinated piglets

Newborn humans and animals are highly susceptible to viral infections. The Aujeszky´s disease virus (ADV) is a porcine herpes virus 1 which infects the respiratory tract and is lethal during the first weeks of life. Current intramuscular vaccines, applied at weaning, induce poor mucosal immunity and frequently fail to prevent and control the disease. Additionally, early vaccination has not been studied thoroughly. Therefore, we studied a systemic/mucosal route of immunization using an inactivated ADV vaccine in two-and fourteen-day-old groups of unweaned SPF miniature Vietnamese pigs, measuring the anti ADV antibody (ELISA) and cytokine (qPCR) responses in systemic and mucosal samples. The results showed that the serum ADV-specific IgG response was higher in the 14-day groups. However, the nasal IgA responses were similar in immunized groups, although the response in saliva was higher in the 2-day old group. Moreover, in vitro ADV stimulated peripheral blood mononuclear cells and lung cells from immunized pigs showed higher IFN-γ mRNA production in the 14-day old group than in younger animals and similar levels of IL-4 and IL-10 transcripts. Our data suggest that early mucosal immunization induce humoral and cellular systemic and mucosal immune responses against ADV in young pigs and younger animals may have compensatory mechanisms to overcome early immaturity and maternal-driven immune interference. Therefore, early protection in susceptible animals could be induced using this immunization protocol, opening the possibility for its application against other viral pathogens of pigs and for traslational studies in humans.

HIV, Cytomegalovirus, and Malaria Infections during Pregnancy Lead to Inflammation and Shifts in Memory B Cell Subsets in Kenyan Neonates

Infections during pregnancy can expose the fetus to microbial Ags, leading to inflammation that affects B cell development. Prenatal fetal immune priming may have an important role in infant acquisition of pathogen-specific immunity. We examined plasma proinflammatory biomarkers, the proportions of various B cell subsets, and fetal priming to tetanus vaccination in cord blood from human United States and Kenyan neonates. United States neonates had no identified prenatal infectious exposures, whereas Kenyan neonates examined had congenital CMV or mothers with prenatal HIV or Plasmodium falciparum or no identified infectious exposures. Kenyan neonates had higher levels of IP-10, TNF-α, CRP, sCD14, and BAFF than United States neonates. Among the Kenyan groups, neonates with prenatal infections/infectious exposures had higher levels of cord blood IFN-γ, IL-7, sTNFR1, and sTNFR2 compared with neonates with no infectious exposures. Kenyan neonates had greater proportions of activated memory B cells (MBC) compared with United States neonates. Among the Kenyan groups, HIV-exposed neonates had greater proportions of atypical MBC compared with the other groups. Although HIV-exposed neonates had altered MBC subset distributions, detection of tetanus-specific MBC from cord blood, indicative of fetal priming with tetanus vaccine given to pregnant women, was comparable in HIV-exposed and non-HIV-exposed neonates. These results indicate that the presence of infections during pregnancy induces fetal immune activation with inflammation and increased activated MBC frequencies in neonates. The immunologic significance and long-term health consequences of these differences warrant further investigation.

Humanized mice, a new model to study the influence of drug treatment on neonatal sepsis

Bacterial infection with group B Streptococcus (GBS) represents a prominent threat to neonates and fetuses in the Western world, causing severe organ damage and even death. To improve current therapeutic strategies and to investigate new approaches, an appropriate in vivo model to study the immune response of a human immune system is needed. Therefore, we introduced humanized mice as a new model for GBS-induced sepsis. Humanized mice feature deficiencies similar to those found in neonates, such as lower immunoglobulin levels and myeloid cell dysfunction. Due to the husbandry in specific-pathogen-free (SPF) facilities, the human immune cells in these mice also exhibit a naive phenotype which mimics the conditions in fetuses/neonates. Following infection, cytokine release and leukocyte trafficking from the bone marrow to the lymphoid organ (spleen) and into the peritoneum (site of infection) as well as bacterial spreading and clearance were traceable in the humanized mice. Furthermore, we investigated the effects of betamethasone and indomethacin treatment using this novel sepsis model. Although both drugs are commonly used in perinatal care, little is known about their effects on the neonatal immune system. Treatment of infected humanized mice not only induced the reduction of human leukocytes in the spleen but also increased the bacterial load in all analyzed organs, including the brain, which did not show infiltration of live GBS in untreated controls. These studies demonstrate the utility of the humanized mice as a new model to study an immature human immune response during bacterial infection and allow the investigation of side effects induced by various treatments.

Human β-defensin 2 expression in ELBW infants with severe necrotizing enterocolitis

BACKGROUND

The aim of this study was to analyze whether the mucosal innate immune response of extremely-low-birth-weight (ELBW) infants might play a role in the development of necrotizing enterocolitis (NEC).

METHODS

Between April 2008 and December 2009 antimicrobial peptides were prospectively measured in fecal samples of ELBW infants. In cases requiring abdominal surgery, full-thickness gut biopsies were analyzed for expression of human β-defensin 2 (hBD2), interleukin-8 (IL-8), villin, MD2, and Toll-like receptor 4 (TLR4).

RESULTS

Fecal hBD1 concentrations were consistently low in all patients, whereas hBD2 concentrations were high in meconium, particularly in clinical chorioamnionitis, and then dropped, followed by a steady increase after day 14. Infants with moderate NEC showed significantly increased fecal hBD2 concentrations before clinical symptoms, in contrast to infants developing severe NEC. Analysis of intestinal resection material obtained from patients with severe NEC revealed low hBD2 mRNA and protein levels, and increased expression of the inflammatory cytokine IL-8.

CONCLUSION

High hBD2 concentrations, reflecting strong intestinal immune responses, were associated with moderate courses of the disease. In severe NEC, low hBD2 expression was accompanied by low TLR4/MD2 expression, suggesting an inadequate response to luminal bacteria, possibly predisposing those infants to the development of NEC.

Effect of praziquantel treatment of Schistosoma mansoni during pregnancy on immune responses to schistosome antigens among the offspring: results of a randomised, placebo-controlled trial

Background

Offspring of women with schistosomiasis may exhibit immune responsiveness to schistosomes due to in utero sensitisation or trans-placental transfer of antibodies. Praziquantel treatment during pregnancy boosts maternal immune responses to schistosome antigens and reduces worm burden. Effects of praziquantel treatment during pregnancy on responses among offspring are unknown.

Methods

In a trial of anthelminthic treatment during pregnancy in Uganda (ISRCTN32849447; http://www.controlled-trials.com/ISRCTN32849447/elliott), offspring of women with Schistosoma mansoni were examined for cytokine and antibody responses to schistosome worm (SWA) and egg (SEA) antigen, in cord blood and at age one year. Relationships to maternal responses and pre-treatment infection intensities were examined, and responses were compared between the offspring of women who did, or did not receive praziquantel treatment during pregnancy.

Results

Of 388 S. mansoni-infected women studied, samples were obtained at age one year from 215 of their infants. Stool examination for S. mansoni eggs was negative for all infants. Cord and infant samples were characterised by very low cytokine production in response to schistosome antigens with the exception of cord IL-10 responses, which were substantial. Cord and infant cytokine responses showed no association with maternal responses. As expected, cord blood levels of immunoglobulin (Ig) G to SWA and SEA were high and correlated with maternal antibodies. However, by age one year IgG levels had waned and were hardly detectable. Praziquantel treatment during pregnancy showed no effect on cytokine responses or antibodies levels to SWA or SEA either in cord blood or at age one year, except for IgG1 to SWA, which was elevated in infants of treated mothers, reflecting maternal levels. There was some evidence that maternal infection intensity was positively associated with cord blood IL-5 and IL-13 responses to SWA, and IL-5 responses to SEA, and that this association was modified by treatment with praziquantel.

Conclusions

Despite strong effects on maternal infection intensity and maternal immune responses, praziquantel treatment of infected women during pregnancy had no effect on anti-schistosome immune responses among offspring by age one year. Whether the treatment will impact upon the offspring's responses on exposure to primary schistosome infection remains to be elucidated.

Trial registration

ISRCTN: ISRCTN32849447

B lymphocyte subsets and their functional activity in the early months of life

In the present study we evaluated B-cell subsets and their functional development in 74 newborns from birth to 6 months of life. Moreover, we evaluated natural antibody production in vitro. The results documented a predominance of naive B-lymphocytes at all time-points evaluated, decreasing from birth to 6 months (p=0.009). The percentages of CD27+IgD+ and CD27+IgDneg memory B-cells were very low at birth and significantly increased only at 6 months (p=0.02 and p less than 0.001, respectively). We found a significant increase only in in vitro stimulated IgG production at 6 months as compared to birth (p less than 0.001). Moreover, a lower secretion of anti-Pn IgM antibodies up to 6 months of age, as compared to controls was observed. Our results underline that the susceptibility and severe course of infection in the neonate can be attributed, at least in part, to the lack of pre-existing immunological memory and competent adaptive immunity.

Early commitment of naïve human CD4(+) T cells to the T follicular helper (T(FH)) cell lineage is induced by IL-12

T follicular helper (T(FH)) cells are a specialized subset of CD4(+) T cells that localize to B-cell follicles, where they are positioned to provide help for the induction of optimal humoral immune responses. Key features of T(FH) cells are the expressions of CXCR5, ICOS, interleukin (IL)-21 and BCL-6. The requirements for human T(FH) cell development are unknown. Here we show that IL-6, IL-12, IL-21 and IL-23 are capable of inducing IL-21 expression in naïve CD4(+) T cells isolated from human tonsils, peripheral blood and cord blood. However, only IL-12 induced sustained expressions of CXCR5 and ICOS on these activated naïve CD4(+) T cells, and endowed them with the ability to provide increased help to B cells for their differentiation into immunoglobulin-secreting cells. The effects of IL-12 were independent of interferon-gamma and T-bet, and associated with upregulation of BCL-6 expression. Thus, these cytokines, particularly IL-12, are likely to act at an early stage during dendritic cell-mediated priming of naïve CD4(+) T cells into a T(FH) cell fate, and thus underpin antibody-mediated immunity.

Antistaphylococcal immunoglobulins to prevent staphylococcal infection in very low birth weight infants

BACKGROUND

Nosocomial infection is a major problem affecting the immediate health and long-term outcome of preterm and very low birth weight neonates. More than half of these infections are caused by staphylococci. Various type specific antibodies targeted at different antigenic markers of Staphylococcus have been developed and have shown promise in animal studies.

OBJECTIVES

To evaluate the efficacy and safety of antistaphylococcal immunoglobulins in the prevention of Staphylococcal infection in very low birth weight infants.

SEARCH STRATEGY

Medline, Embase, CINAHL, Cochrane Central Register of Controlled Trials (The Cochrane Library) were searched from their inception until February 2009. In addition, abstracts of major pediatric meetings of last seven years were searched.

SELECTION CRITERIA

Randomized and quasi-randomized studies of antistaphylococcal immunoglobulins for the prevention of staphylococcal infections in preterm or very low birth weight neonates were reviewed by both authors for their eligibility for inclusion. Studies of any dose and/or route were included. Quality of studies was evaluated using criteria of masking of randomization, masking of intervention, completeness of follow-up and masking of outcome assessment by both review authors.

DATA COLLECTION AND ANALYSIS

Data from the primary author were obtained where published data provided inadequate information for the review or where relevant data could not be abstracted. Data were abstracted independently by both review authors. Statistical methods included calculation of relative risk (RR), risk difference (RD), number needed to treat (NNT) and weighted mean difference (WMD) when appropriate. Ninety five percent confidence intervals (CI) was used for these estimates of treatment effects. A fixed effect model was used for meta-analyses.

MAIN RESULTS

Three eligible studies were included (two studies of INH A-21 and one study of Altastaph involving a total of 2,701 neonates). Three reports of Pagibaximab were published as abstracts and will be considered for inclusion when further information is obtained. There were no significant differences noted in the risk of Staphylococcal infection between INH A-21 vs. placebo (typical RR 1.07, 95% CI 0.94, 1.22) or Altastaph vs. placebo (RR 0.86, 95% CI 0.32, 2.28); the risk of other bacterial infection between INH A-21 vs. placebo (typical RR 0.87, 95% CI 0.72, 1.06) or Altastaph vs. placebo (RR 0.93, 95% CI 0.53, 1.64); or the risk of any infection between INH A-21 vs. placebo (RR 1.00, 95% CI 0.91, 1.09) or Altastaph vs. placebo (RR 0.93, 95% CI 0.54, 1.62). There was no significant difference in the incidence of relevant secondary outcomes (chronic lung disease at 28 days, patent ductus arteriosus, necrotizing enterocolitis, intraventricular hemorrhage, retinopathy of prematurity or duration of antibiotic and vancomycin use).

AUTHORS' CONCLUSIONS

Antistaphylococcal immunoglobulins (INH A-21 and Altastaph) are not recommended for prevention of staphylococcal infections in preterm or VLBW neonates. Further research to investigate the efficacy of other products such as Pagibaximab is needed.

Fetal immune responses to Plasmodium falciparum antigens in a malaria-endemic region of Cameroon

Plasmodium falciparum infection during pregnancy can lead to the transplacental passage of malarial Ags that are capable of inducing acquired immune responses in the fetus. Studies have identified cytokines produced by malaria-specific cord blood (CB) T cells, but information on fetal B cells is limited. Thus, CB mononuclear cells from 120 Cameroonian newborns were cultured for 7 days in vitro and supernatants were assessed by ELISA for Abs to an extract of malarial schizonts (MA), recombinant apical merozoite Ag 1 (AMA-1), the 42-kDa C-terminal region of merozoite surface protein 1 (MSP-1(42)), a B epitope of ring-infected erythrocyte surface Ag (RESA), and the dominant B epitope of the circumsporozoite protein (CSP). Only 12% of supernatants contained IgM to MA but 78% had IgG to one or more malarial Ags, with 53% having IgG to AMA-1, 38% to MSP-1(42), 3% to RESA, and 0% to CSP. The Abs to AMA-1 and MSP-1(42) were predominantly IgG1 and IgG3. CB mononuclear cells were also tested for the ability to secrete cytokines in response to MA and a pool of conserved MSP-1 T cell epitopes. Among the Ag-reactive samples, 39.3% produced only Th2-type cytokines, whereas 60.6% produced a combination of Th1- and Th2-type cytokines. Although a Th2 bias was observed, the in utero cytokine environment was adequate to support isotype switching to cytophilic IgGs, the isotypes that are protective in adults. Because many infants living in a low transmission area are born with malaria-specific B and T cells, the influence of in utero priming on neonatal immunity merits further investigation.

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.

Dexamethasone inhibits maturation and alters function of monocyte-derived dendritic cells from cord blood

Critically ill infants are treated with dexamethasone (Dx) and other glucocorticoids to reduce inflammation and to promote lung and cardiac function. The neonatal immune system is immature, so neonatal dendritic cells (DCs) might be especially sensitive to glucocorticoid-mediated immunosuppression. To test this, we compared Dx treatment of monocyte-derived DCs from cord (CB) and adult blood (AB). Dx decreased CD1a levels on both AB and CB DCs. CB-treated cells also exhibited decreased expression of CD83 and increased expression of CD14, alterations not observed in AB DCs. Characteristic immature endocytic activity was sustained and enhanced in Dx-treated CB DCs, whereas AB DCs matured normally. Maintenance of endocytosis corresponded with CD14 expression. Dx markedly increased CB DC IL-10, a T cell helper 2 (Th2)-preferential cytokine, while reducing IL-12, a counterbalancing Th1 cytokine. AB DCs were also affected, but increases in IL-10 and decreases in IL-12 were more modest. Dx treatment also inhibited DC-induced T cell proliferation, but CB DCs were inhibited more. In short, neonatal DCs seemed to be especially sensitive to the immunosuppressive effects of Dx as indicated by altered phenotype, endocytic function, ability to stimulate T cells, and cytokine shift favoring Th2. These alterations in DC function are consistent with an increased risk for certain infections and atopic diseases.

Monocyte switch in neonates: high phagocytic capacity and low HLA-DR expression in VLBWI are inverted during gestational aging

Pre-term neonates are at high risk to develop early-onset sepsis which possibly is caused by an immature immune system. Monocytes play a pivotal role as professional phagocytic and antigen-presenting cells in the innate immunity. In the present study, we investigated in monocytes from cord blood the expression of human leukocyte antigen (HLA)-DR as a marker for antigen-presenting capability, the expression of the high-affinity receptor for IgG (FcgammaRI/CD64), and the capacity to phagocytize non-opsonized Escherichia coli. We compared 70 infants in three groups according to their gestational age (group I: 20 very low birth weight infants (VLBWI), 24-31 weeks of gestation; group II: 25 pre-term infants, 32-36 weeks of gestation, and group III: 25 term neonates). The expression of CD64 as well as the phagocytic capacity of monocytes from cord blood were highest in VLBWI (p < 0.05 and p < 0.01, respectively). In contrast, HLA-DR expression was significantly (p < 0.05) diminished in VLBWI, which possibly leads to a reduced antigen-presenting capacity. We conclude that monocytes have different functional properties during gestational aging, which perhaps participate in the high incidence of infections in VLBWI.

Clinical microbiology of bacterial and fungal sepsis in very-low-birth-weight infants

Twenty percent of very-low-birth-weight (<1500 g) preterm infants experience a serious systemic infection, and despite advances in neonatal intensive care and antimicrobials, mortality is as much as threefold higher for these infants who develop sepsis than their counterparts without sepsis during their hospitalization. Outcomes may be improved by preventative strategies, earlier and accurate diagnosis, and adjunct therapies to combat infection and protect the vulnerable preterm infant during an infection. Earlier diagnosis on the basis of factors such as abnormal heart rate characteristics may offer the ability to initiate treatment prior to the onset of clinical symptoms. Molecular and adjunctive diagnostics may also aid in diagnosing invasive infection when clinical symptoms indicate infection but no organisms are isolated in culture. Due to the high morbidity and mortality, preventative and adjunctive therapies are needed. Prophylaxis has been effective in preventing early-onset group B streptococcal sepsis and late-onset Candida sepsis. Future research in prophylaxis using active and passive immunization strategies offers prevention without the risk of resistance to antimicrobials. Identification of the differences in neonatal intensive care units with low and high infection rates and implementation of infection control measures remain paramount in each neonatal intensive care unit caring for preterm infants.

Distinctive response of naïve lymphocytes from cord blood to primary activation via TCR

Umbilical cord blood (UCB) is now being considered an alternative to bone marrow for restoring hematopoiesis after myeloablative therapy. The lower risk of acute and chronic graft-versus-host disease in patients who received UCB cells seems related to the nature of UCB-T cells. Phenotypically, UCB-CD3+ cells are mostly naive (CD45RA+) and represent a transitional population between thymocytes and adult T cells. We examined the immune reactivity of highly purified, negatively selected CD4+CD45RA+ cells by mimicking activation via T cell receptor (TCR). All experiments included the extensively characterized adult peripheral blood (APB) cells as reference. On the contrary to APB, naive UCB-CD4+ cells were able to proliferate with anti-CD3 stimulation alone. With addition of interleukin (IL)-2 or costimulatory signal, both populations reached similar proliferation. Forty-eight hours after anti-CD3 stimulation, CD4+CD45RA+ from UCB, but not APB, showed characteristic blastic morphology and significant expression of CD25 on the surface. A low concentration of IL-2 was detected at 24 h by anti-CD3-stimulated UCB CD4+CD45RA+, which rapidly disappeared. By 72 h after activation, CD4+CD45RA+ UCB cells showed extensive apoptosis, whereas CD4+CD45RA+ APB cells showed low levels of apoptosis. Using RNase protection assay, we observed that CD95L levels were significantly higher in naive CD4+ cells from UCB than from APB after activation. However, neutralizing Fas-Fc protein was unable to inhibit anti-CD3-induced apoptosis, suggesting that this was a CD95-independent mechanism. These results indicate that UCB-CD4+CD45RA+ cells are able to start proliferating as a result of early IL-2 production after TCR engagement alone, but probably, as a result of the consumption of this IL-2, they undergo cell death.

Transient detection of proinflammatory cytokines in sera of colostrum-fed newborn calves

To obtain basic information on the state of proinflammatory cytokines in newborn calves, we determined the kinetics of 5 cytokines (IL-1beta, IL-6, TNF-alpha, IFN-gamma and IL-1 receptor antagonist) in sera of newborns during the first 4 weeks of life. At birth, none of the 5 cytokines were detected in almost all serum samples, but the cytokines became detectable within 12 hr after being fed colostram. The mean concentrations of the cytokines reached peak levels by 24 hr and then gradually decreased and became undetectable by 4 weeks after birth. Cytokine mRNA expressions in peripheral blood mononuclear cells of newborns were observed without reference to the cytokine concentrations in sera. Serum cytokines detected in newborn calves are probably colostral origin.

Generation of recombinant human monoclonal antibodies to rotavirus from single antigen-specific B cells selected with fluorescent virus-like particles

Technical difficulties have severely limited the yield of methods for the generation of human antiviral monoclonal antibodies (Mabs) in the past. We describe here a novel method for the efficient development of human Mabs against viruses. Rotavirus (RV) is a major cause of gastroenteritis in infants and adults worldwide. We generated fluorescent virus-like particles (VLPs) to identify and physically sort single RV-specific B cells from healthy adult blood donors, or RV-infected infants or adults. We expanded the sorted single B cells in culture, tested for RV-specific antibody secretion, and cloned and sequenced the antibody heavy and light chain variable region (VH and VL) genes. The percentage of wells that produced antibodies after sorting and expanding RV-specific adult B cell clones was high at 23%. The overall efficiency of RV-specific antibody gene recovery after the isolation, confirmation, and cloning of RV-specific VH segments was 1.3% of sorted cells in adults. RV-specific variable gene segments also were obtained from acutely infected infants, although infant B cells did not proliferate and differentiate in culture as well as adult B cells. We expressed recombinant Fabs incorporating the VH and VL genes from RV-specific B cell clones using a new modified bacterial Fab expression vector that we describe. Finally, we demonstrated binding of purified Fabs to RV proteins by immunofluorescence and ELISA. This method for the generation of recombinant human Mabs to RV from single antigen-specific B cell clones selected with fluorescent VLPs could be used to generate human Mabs to many other viruses whose proteins can self-assemble into VLPs.

Monocyte phagocytosis as a reliable parameter for predicting early-onset sepsis in very low birthweight infants

BACKGROUND

Septic complications lead to a high mortality rate in very low birthweight infants (VLBWI). Therefore, prognostic markers for the development of sepsis attach importance to start an efficient therapy as early as possible.

AIMS

Functional and phenotypical variables of blood monocytes in the cord and peripheral blood were investigated to evaluate the parameters for predicting early-onset and late-onset sepsis (nosocomial infections).

STUDY DESIGN

In a prospective study, 25 VLBWI were investigated.

METHODS

In the cord blood taken immediately after birth, the capacity of the monocytes to phagocytose non-opsonized E. coli bacteria by flow cytometry and the ex-vivo production of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1 beta and IL-6 (enzyme-linked immunoassay (ELISA)) after lipopolysaccharide (LPS) stimulation were measured. At the third day, the HLA-DR expression on the monocytes (flow cytometry) and the LPS-induced cytokine production were measured from the peripheral blood.

RESULTS

Five VLBWI already developed early septic complications after 24-72 h, while the other three infants had late-onset sepsis 10-18 days after birth. The prognostic significance for early-onset sepsis was highest for the decreased monocyte phagocytic capacity (sensitivity and specificity: 100%) and for the LPS-induced formation of TNF-alpha and IL-1 beta in cord blood. Moreover, in septic VLBWI, the HLA-DR expression on the monocytes was lowered on day 3 after birth. The prognostic significance for late-onset sepsis was highest for TNF-alpha and IL-1 beta levels in the peripheral blood on the third day after birth.

CONCLUSIONS

The determination of phagocytosis in the cord blood seems to be a reliable parameter for predicting early-onset sepsis and offers the possibility for a forward start of an antibiotic therapy.

Interleukin 10, produced in abundance by human newborn T cells, may be the regulator of increased tolerance associated with cord blood stem cell transplantation

The use of human umbilical cord blood as an alternative source of stem cells to bone marrow for the reconstitution of the immune system is associated with less frequent and less severe incidence of graft-versus-host disease (GVHD). This study focuses on aspects of cord blood T-cell biology that may contribute to a perceived increased tolerance associated with the neonatal immune response. A skewing of the T-helper (Th)1/Th2 phenotype of cord blood T cells towards a Th2 response has frequently been cited as a possible cause. In this study, primary and repeated stimulation via the T-cell receptor (TCR) complex induced a Th0-type cytokine response, with both adult and cord blood-derived naïve T cells producing interferon gamma (IFN-gamma), interleukin 4 (IL-4) and IL-5. IL-10 was induced in cord blood T-cell cultures during primary stimulation, while adult T cells began to secrete IL-10 only after repeated stimulation. The presence of the antigen-presenting cell (APC)-derived cytokine IL-1beta inhibited IL-10 production by cord blood cells. The effects of IL-12 and IL-4 on T-cell cytokine responses were also examined. In addition to their differential Th1/Th2 skewing effects on cord and adult T cells, both cytokines augmented IL-10 production in both T-cell populations. These findings demonstrate that cord blood T cells may secrete large amounts of the anti-inflammatory cytokine IL-10 and that the presence of IL-1beta or Th1/Th2 skewing cytokines can regulate its production. This data provides support for the recognized tolerant nature of the newborn immune response that may contribute to the reduced incidence of GVHD associated with cord blood transplantation.

T cell immunity in neonates

Typically, neonates exhibit decreased or aberrant cellular immune responses when compared to adults, resulting in increased susceptibility to infection. However, it is clear that newborns are able to generate adult-like protective T cell responses under certain conditions. The focus of our research is to understand the deficiencies within the neonatal immune system that lead to improper cellular responses and how priming conditions can be altered to elicit the appropriate T cell response necessary to protect against development of pathogen-induced disease. With these goals in mind, we are exploring the attributes of neonatal T cells and their development, as well as the conditions during priming that influence the resulting response to immune challenge during the neonatal period.

[Development of specific immunity in prenatal life]

The various defense mechanisms of specific immunity, which involves the T and B lymphocytes and the antigen presenting cells, are gradually developed during intra-uterine life. The first hematopoietic organ is the yolk sac which appears at the 4th week of development. Thereafter, the hematopoiesis takes place in the fetal liver (from the 6th week) followed by the bone-marrow during the 3rd trimester. The differentiation of the T lymphocytes begins around the 10th week. The thymic epithelial rudiments appear during the 7th week and the thymus migrates to its definitive place at ten weeks. It is then colonized by the T cell precursors, which there undergo their maturation process. From the 12th week of development, mature T cells are readily detectable in lymphoid organs and fetal blood. The maturation of B cells, which occurs firstly in fetal lever, and thereafter in bone marrow begins also early in fetal life (12th week). The antigen presenting cells, the precursors of which are detected in the yolk sac as soon as 4-6 weeks, are normally present and functional in secondary lymphoid organs as soon as 12 weeks. Thus, the specific immune response appears possible by the end of the 1st trimester. However, the naive nature of T and B lymphocytes is responsible for a delayed, slow and relatively ineffective primary response. This observation explains the particular susceptibility of neonates, especially premature neonates to bacterial and viral infections. The various antigenic stimulations and T/B cell cooperations allow a complete maturation of the immune system during the first years of life.

Human double-negative T cells in systemic lupus erythematosus provide help for IgG and are restricted by CD1c

To understand the mechanism of T cell help for IgG production in systemic lupus erythematosus (SLE) we investigated the response of CD4- and CD8-negative (double-negative (DN)) T cells because 1) DN T cells are present at unusually high frequency in patients with SLE and can induce pathogenic autoantibodies; 2) the DN T cell repertoire includes cells restricted by CD1 Ag-presenting molecules; and 3) CD1c is expressed on a population of circulating B cells. We derived DN T cell lines from SLE patients and healthy individuals. In the presence of CD1(+) APCs, DN T cell lines from SLE patients produced both IL-4 and IFN-gamma, whereas DN T cells from healthy donors produced IFN-gamma, but no IL-4. In general, cells from patients with highly active disease produced high levels of IFN-gamma; cells from those with little activity produced high IL-4. Coculture of CD1c-directly reactive T cells from healthy donors with CD1c(+) B cells elicited IgM Abs, but little or no IgG. In contrast, CD1c-directly reactive T cells from SLE patients induced isotype switching, with a striking increase in IgG production. Neutralizing Abs to CD1c inhibited the ability of DN T cells to induce IgG production from CD1c(+) B cells, further indicating that CD1c mediated the T and B cell interaction. IgG production was also inhibited by neutralizing Abs to IL-4, correlating with the cytokine pattern of DN T cells derived from these patients. The data suggest that CD1c-restricted T cells from SLE patients can provide help to CD1c(+) B cells for IgG production and could therefore promote pathogenic autoantibody responses in SLE.

Expression of the costimulator molecules, CD40 and CD154, on lymphocytes from neonates and young children

Differential expression of the costimulator molecules CD40 and CD154 on neonatal lymphocytes may be one explanation for limited T-dependent antibody responses in human neonates. CD40 was expressed at similar levels on resting B cells from adults, young children (2-20 months of age) or cord blood. CD40 expression was higher on cord blood B cells compared to adult B cells after stimulation with PMA and ionomycin, but similar on adult and cord blood B cells activated by CD3-stimulated T cells. In contrast to previous reports, cord blood T cells stimulated with PMA and ionomycin expressed adult levels of CD154 initially, but this expression was more transient on cord blood T cells. When adult and cord blood mononuclear cells were stimulated with CD3 mAb, T cells from some cord blood specimens showed different kinetics of CD154 expression compared with adult T cells. However, some cord blood specimens showed adult patterns of T cell CD154 expression. When mononuclear cells were depleted of B cells and monocytes prior to stimulation with CD3 mAb, the MFI and percentage of T cells expressing CD154 increased, with adult and cord T cells showing similar patterns of expression. These results show some differences in expression of CD40 and CD154 between neonatal and adult lymphocytes, but do not directly account for the relative deficiencies of humoral immunity in neonates.

The importance of being receptive

Neuroendocrine system and immune system can communicate via the use of soluble mediators like hormones, neurotransmitters and cytokines. The level of mediators secreted by either of these systems creates the milieu in which immune and neuroendocrine responses take place. For adequate communication between the systems, receptors for hormones, neurotransmitters and cytokines are required. This review describes the role of regulated expression and function of receptors for hormones and neurotransmitters within the immune system in neuroendocrine-immune communication.

Expression of the costimulator molecules, CD80, CD86, CD28, and CD152 on lymphocytes from neonates and young children

The expression of CD80, CD86, CD28, and CD152 were examined on peripheral blood lymphocytes from adults, neonates (cord blood lymphocytes) and young children (2-20 months of age). There was no difference in the expression of CD80 or CD86 between adult and neonatal B cells, either resting or activated. A higher percentage of resting T cells expressed CD28 in neonates and young children compared to adults. CD28 expression was similar on adult and neonatal T cells activated with PMA and ionomycin. However, CD28 was expressed at greater intensity on a higher percentage of neonatal T cells than adult T cells stimulated with CD3. CD152 expression was lower on neonatal T cells than adult T cells stimulated with PMA and ionomycin and undetectable on neonatal T cells stimulated with CD3. In contrast, intracellular CD152 was equivalent in adult and neonatal T cells stimulated with PMA and ionomycin, suggesting trafficking of CD152 to the cell surface may be differentially regulated in neonatal T cells. Since the T cell response is determined by the balance of signals received from CD28 and CD152, high levels of CD28 expression and lower surface expression of CD152 on neonatal T cells may represent specialisation to promote activation of neonatal T cells.

T-cell function in newborn mice and humans

Neonates mount poor immune responses, and it has been assumed that neonatal T cells differ qualitatively from adult T cells. Here, Becky Adkins discusses this issue in the light of recent data indicating that T cells in neonates are developmentally mature in their capacity to mount protective Th1-type and cytotoxic T lymphocyte responses.

Rapid conversion of naive to effector T cell function counteracts diminished primary human newborn T cell responses

The reduced incidence of graft versus host disease following the use of human cord blood as a source of stem cells for bone marrow reconstitution challenges our understanding of the immunocompetence of newborn T cells. Newborn CD4+ T cells express mainly the CD45RA phenotype and have been considered to respond comparably to adult CD4+ T cells exhibiting the CD45RA phenotype. We compared the in vitro kinetics of phenotypic conversion of newborn and adult CD4+CD45RA+ T cells to CD4+CD45RO+ T cells. The cytokine profile and B cell helper activity of the converted CD4+CD45RO+ T cell population were also determined. Newborn CD4+CD45RA+ T cells were converted to CD4+CD45RO+ with significantly faster time kinetics than adult CD4+CD45RA+ T cells, following either phytohaemagglutinin (PHA) or anti-CD2 activation. Freshly purified newborn naive T cells did not produce IL-2, IL-4 or interferon-gamma (IFN-gamma) following stimulation, whereas adult naive T cells secreted IL-2 and adult-derived CD4+CD45RO+ T cells secreted all three cytokines under the same stimulatory conditions. However, newborn and adult CD4+CD45RA+ T cells, following primary stimulation and maturation in vitro, acquired the ability to secrete a Th1-type cytokine profile of IL-2 and IFN-gamma after secondary stimulation. Newborn CD4+ naive T cells that acquired the CD45RO phenotype in vitro also gained B cell helper activity equivalent to that of adult in vitro matured CD4+ naive T cells. These findings suggest that newborn and adult CD4+CD45RA+ T cell subsets are differentially responsive to various stimuli. They show that newborn CD4+CD45RA+ naive T cells can transform more quickly than their adult counterparts into functionally equivalent CD4+CD45RO+ T cells, a process that may be important to counteract the immature immune environment which exists in the newborn.

Defective IL2 gene expression in newborn is accompanied with impaired tyrosine-phosphorylation in T cells

Here we confirmed that IL2 mRNA expression in CD3-stimulated T cells is defective at birth. Because protein-tyrosine phosphorylation is an important part of signaling through CD3 and plays a key role in IL2 transcription, we further investigated whether impaired IL2 response to CD3 in newborns would be accompanied with an alteration of tyrosine phosphorylation. In this purpose, CD3-induced tyrosine phosphorylation was evaluated comparatively in newborn and adult cells by immunoblotting of total cellular extract with an antiphosphotyrosine antibody. Results show that, in both peripheral lymphocytes or purified CD4 T cells from both cord and adult, CD3 stimulation could induce small even significant tyrosine-phosphorylation. Tyrosine phosphorylation occurs as soon as 2' following CD3 ligation and was still evident up to 15-20'. Yet, by using a highly sensitive method to analyze CD3-induced accumulation of phosphorylated substrates, which consisted in adding pervanadate, an inhibitor of phosphatases, during the last 2 min of CD3 stimulation, we showed that the intensity of tyrosine phosphorylation was clearly decreased in cord cells. From these results, it is tempting to speculate that suboptimal capacities of cord T cells to up-regulate tyrosine phosphorylation might contribute to defective IL2 production in neonates.

Ontogeny of the fetal immune system: study on pregnancies with Rh-isoimmunization and nonimmune fetal hydrops

This study aims at observing and comparing the antigen expression of some fetal T- and B-lymphocyte subpopulations in Rh-isoimmunization, which determines anemic hypoxia in the fetus, and nonimmune fetal hydrops (NIFH) which, even if there are some etiological factors involved, causes hipoxic hypoxia in the fetus. Twelve fetuses were studied by way of 30 fetal blood samples obtained by ultrasound-guided cordocentesis between the 20th and 36th gestational week. Twenty-four blood samples in all where taken from the eight fetuses with Rh-isoimmunization. Six blood samples were obtained from the four fetuses with NIFH. The lymphocyte phenotypes studied by monoclonal antibodies and flow cytometry were the following: CD3, CD4, CD8, expression of T-lymphocyte subpopulations; BsIg, CD19, expression of B-lymphocyte subpopulations. We observed a near-normal maturation process in fetuses with Rh isoimmunization, whereas in fetuses with NIFH we observed inhibition and/or delayed expression of T-lymphocytes. An early and increased B-lymphocyte activation marked a cooperation between the two systems in the early gestational periods.

Absence of IgD-CD27(+) memory B cell population in X-linked hyper-IgM syndrome

The present study analyzed peripheral blood B cell populations separated by IgD and CD27 expression in six males with X-linked hyper-IgM syndrome (XHIM). Costimulation of mononuclear cells from most of the patients induced no to low levels of class switching from IgM to IgG and IgA with Staphylococcus aureus Cowan strain (SAC) plus IL-2 or anti-CD40 mAb (anti-CD40) plus IL-10. Measurable levels of IgE were secreted in some of the patients after stimulation with anti-CD40 plus IL-4. Costimulation with SAC plus IL-2 plus anti-CD40 plus IL-10 yielded secretion of significant levels of IgG in addition to IgM, but not IgA. The most striking finding was that peripheral blood B cells from all of the six patients were composed of only IgD+ CD27(-) and IgD+ CD27(+) B cells; IgD- CD27(+) memory B cells were greatly decreased. IgD+ CD27(+) B cells from an XHIM patient produced IgM predominantly. Our data indicate that the low response of IgG production in XHIM patients is due to reduced numbers of IgD- CD27(+) memory B cells. However, the IgG production can be induced by stimulation of immunoglobulin receptors and CD40 in cooperation with such cytokines as IL-2 and IL-10 in vitro.

Removal of erythroid cells from umbilical cord blood mononuclear cell preparations using magnetic beads and a monoclonal antibody against glycophorin A

Umbilical cord blood mononuclear cells isolated by density centrifugation are contaminated by erythrocytes and nucleated erythroid precursors which may exceed 50% of the total cell population, and thus interfere with phenotypic, functional and mRNA analyses. Lysis with hypotonic ammonium chloride can overcome this problem, but interferes with lysosomal function and should be avoided when cell preparations are intended for functional studies. The aim of this study was to develop a technique for removing erythroid cells from cord blood mononuclear cell preparations that would be as effective as ammonium chloride lysis but would not affect cellular function. This paper describes a method using 10F7, a mouse monoclonal antibody against human glycophorin A, and magnetic beads coated with anti-mouse immunoglobulin. The population of cord blood mononuclear cells recovered using this technique was of high purity, good yield and viability, and the cells responded appropriately to stimulation in vitro. To maximise cost-effectiveness, purification with magnetic beads could be performed after two density separations to reduce the quantity of beads required.

Infant B cell responses to polysaccharide determinants

Newborns and infants up to the age of 1.5-2 years of age are unable to produce antibodies to bacterial capsular polysaccharides. As a consequence, children up to the age of 2 years have an increased susceptibility for infections with encapsulated bacteria. Capsular polysaccharides are classified as so-called T cell independent type 2 antigens and induce IgG2 antibodies. The mechanism of B lymphocyte activation by polysaccharides differs from that of protein antigens and involves co-stimulation by CD21 (type 2 complement receptor). Reduced expression of CD21 on neonatal B lymphocytes can explain unresponsiveness to polysaccharides. Polysaccharide protein conjugates have the ability to overcome unresponsiveness to polysaccharides early in life. The response induced is predominant IgGl.

B Cell Sensitization to Helminthic Infection Develops In Utero in Humans

Human neonates are generally deficient in their ability to generate humoral immunity. This deficiency is thought to reflect physiologic immaturity of T and B cell function and lack of previous exposure to exogenous Ags. To determine whether neonatal humoral immunity can be modified by maternal helminth infection during pregnancy, we assessed Ig production by cord blood lymphocytes from healthy newborns of mothers living in an area of Kenya where schistosomiasis, bancroftian filariasis, and geohelminth infections are endemic. Twelve of 40 and 17 of 39 cord blood lymphocyte preparations from healthy newborns in Coast Province, Kenya, spontaneously made polyclonal IgE (range, 0.15–21 ng/ml) and IgG (1.6–10.1 ng/ml) in vitro. In vitro IgE synthesis by cord blood lymphocytes (CBL) was, on the average, 10-fold less than that of PBMC of Kenyan mothers (1.1–98 ng/ml) and was undetectable for CBL from newborns delivered in the United States. Schistosome and filarial Ags stimulated a 3- to &gt;100-fold increase in the production of polyclonal IgE and parasite-specific IgG Abs by lymphocytes from 10 of 40 and 6 of 39 Kenyan newborns, respectively. CBL observed to have helminth Ag-driven B cell responses were more likely to be from newborns of schistosome- or filaria-infected mothers than from uninfected mothers (p &lt; 0.05). These data indicate that the human fetus can be sensitized in utero to produce helminth-specific B cells and that neonatal B cells are intrinsically capable of IgE and IgG production.

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 development of antibody responses in the infant

The human infant is a major subject of immunization to prevent infectious disease. A better understanding of immune responses in human infants could lead to more effective immunization. Analysis of individual mechanisms is a prerequisite to understanding the whole response. We have examined the mutation and selection of immunoglobulin genes, mechanisms required for the maturation of antibody affinity. Mutations were rare in cord blood and were not detected in peripheral blood of infants under 10 days of age. Mutations were detected in most blood samples from infants aged 10 days to 2 months but the number of mutations was generally low compared with adults and there was limited evidence of selection. The ability to make and select mutated Ig increased over the 2-8 months period, but did not reach adult levels. Neonates differ from adults in the expression of several components of the immune system that may take part in affinity maturation, including cytokine receptors, antigen receptor and co-stimulator molecules. Thus, the mechanisms required to make high-affinity antibody develop gradually during the first year of life. Possible evolutionary reasons for this are discussed.

Analysis of neonatal T cell and antigen presenting cell functions

Neonates are more susceptible to infection than adults and exhibit more intense or prolonged clinical symptoms. The extent to which deficiencies in T cell or antigen presenting cell (APC) function underlie hyporesponsiveness is incompletely understood. Here, immune function of cord blood mononuclear cells (CBMC), from healthy, full-term neonates was compared with adult PBMC. As widely reported, polyclonally-stimulated T cell proliferation was found to be equivalent, while IFN gamma responses were markedly lower amongst neonates. Reasoning that such stimuli may elicit responses qualitatively different from those that would be obtained following MHC-dependent, cognate T cell activation, alloantigen-specific responses were evaluated. Strikingly, neonates exhibited IFN gamma, IL-4 and IL-10 production equal to adults in short term primary culture. Both the frequency (Fisher's p < 0.0004) and intensity (< 7.5 vs 36.5 pg/ml; Wilcoxon P = 0.005) of alloantigen stimulated IL-5 responses were elevated among neonates, a finding equally evident using irradiated adult or neonatal cells as stimulators. Finally, the relative capacity of neonatal APC as stimulators of cytokine synthesis was assessed by a novel approach using CBMC as both responders and stimulators in MLR. Irradiated neonatal cells consistently stimulated similar proliferative but substantially lower IFN gamma responses than did adult APC, independent of responder origin. The data argue; (i) T cells are largely immunocompetent at birth, (ii) accessory cell function is not fully mature, and (iii) the widely observed hyporesponsiveness to pathogenes may be primarily due to immaturity of APC function or costimulator molecule expression.

The value of immunoglobulin and complement levels in the early diagnosis of neonatal sepsis

Serum IgG, IgG1, G2, G3, G4, IgM, C3c and C4 concentrations were measured in 24 term neonates with sepsis and 17 healthy normal neonates of similar age, sex and weight (control group). The serum IgG, IgG1, G2, G3, G4, IgM, C3c, and C4 levels were similar in the patients with sepsis and the control group (p > 0.05). In the neonates with sepsis, serum IgG, G1, G2, IgM and C4 levels were not significantly different between the 1st and 10th days, while there were significant differences for IgG3, G4 and C3c (p < 0.05). We conclude that the serum levels of IgG, IgG1, G2, G3, G4, IgM, C3c and C4 concentrations are of no value for the early diagnosis of neonatal sepsis.

B cell subpopulations separated by CD27 and crucial collaboration of CD27+ B cells and helper T cells in immunoglobulin production

B cell immunoglobulin production is regulated by helper T cells through direct interaction and secreted cytokines. In the present study, we functionally analyzed CD27 in cord and peripheral blood B cells. Adult peripheral blood B cells were separated into CD27+ and CD27- cells, which differed in their morphology. Cord blood B cells did not express CD27, and CD27 expression on peripheral blood B cells increased with age. Only CD27+ B cells had the ability to produce immunoglobulin, which was increased by contact with a tumor necrosis factor-related transmembrane ligand, CD70. Adult peripheral blood CD27+ B cells can be further subdivided into two discrete subtypes: IgD- CD27+ and IgD+ CD27+ B cells. IgD- CD27+ B cells produce IgG, IgM and IgA, whereas IgD+ CD27+ B cells predominantly produce IgM. The addition of activated CD4+ CD45RO T cells expressing CD70 caused down-regulation of CD27 expression on activated B cells, and this down-modulation was completely blocked by anti-CD70 monoclonal antibody, indicating direct T-B cell contact via CD27/CD70. The triggering via CD27 and CD40 additively increased the immunoglobulin production under Staphylococcus aureus Cowan strain plus interleukin-2 stimulation. Taken together, our findings demonstrate that peripheral blood B cells are separated into subpopulations by CD27 and IgD expression and that CD27+ B cells produce large amounts of immunoglobulin by interaction with the CD70 molecule.

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.

Antigen-independent responsiveness to interleukin-4 demonstrates differential regulation of newborn human T cells

The low incidence of graft-versus-host disease following clinical use of umbilical cord blood compared to adult bone marrow as a source of stem cells for bone marrow reconstitution, leads to questions concerning the level of immunocompetence of newborn T cells. The maturation and functional status of newborn CD4+ T cells, which are almost exclusively CD45RA+ naive T cells, compared with their adult phenotypic counterparts, is poorly understood. We examined the proliferative response to mitogens and cytokines of CD4/CD45RA+ T cells from adults and newborns, with and without accessory cells. Newborn CD4/CD45RA+ T cells demonstrated a distinct proliferative response profile which was determined by the number of accessory cells present in co-cultures with various stimuli. Newborn CD4/CD45RA+ T cells were particularly responsive to interleukin (IL)-4, IL-4 plus anti-CD2 monoclonal antibodies (mAb) and IL-4 plus phytohemagglutinin (PHA), whereas adult CD4/CD45RA+ T cells were unresponsive under similar conditions. The mitogenic responses of newborn and adult CD4/CD45RA+ T cells to PHA and anti-CD2 mAb, which were equivalent, were directly proportional to the number of accessory cells present, whereas the responsiveness to cytokines was inversely proportional to the number of co-cultured accessory cells. Anti-CD2 responses were much more sensitive to low numbers of accessory cells than PHA. The particular sensitivity of newborn CD4/CD45RA+ T cells to IL-4 represents an antigen-independent T cell activation response which could help promote a Th2 immune response resulting in the newborn.

Functional antagonism between IL-2 and PGA1 or PGJ2 in the control of proliferation of human cord blood-derived mononuclear cells

Cyclopentenone prostaglandins PGA1 and PGJ2 induce growth arrest at the G1/S interphase of the cell cycle in tumour cell lines. Notably, PGE, the precursor molecule of PGA, downregulates the interleukin (IL)-2-dependent proliferation of lymphocytes. Therefore the IL-2/IL-2 receptor system and relative signal transduction is a possible target of the antiproliferative effect of PGA/PGJ. In the present study the PGA1/PGJ2-dependent growth inhibition of IL-2-stimulated primary human cord blood mononuclear cells (CBMCs) was found to be mediated by interference with the IL-2 proliferative signal. Both prostaglandins (PGs) inhibited the synthesis of total RNA and protein in IL-2 stimulated cells. PGA1 and even more PGJ2 downregulated the expression of IL-2 receptor alpha (CD25 phenotype). IL-2 partly reversed this effect. Moreover, suppression of IL-2-stimulated cells was not the result of PG-mediated activation of apoptosis. On the contrary, PGs reduced both apoptosis and the high expression of c-Jun detectable in CBMCs spontaneously. Cyclin A/Cdk2 complexes regulate G1/S transition during the cell cycle. In IL-2-stimulated cells, the levels of Cdk2 were found to be lower in PG-treated cells than those detected in controls. In conclusion, cyclopentenone PGs inhibit CBMCs spontaneous or IL-2-dependent proliferation in part by interfering with the IL-2 pathway.