Cellular and molecular mechanisms for reduced interleukin 4 and interferon-gamma production by neonatal T cells

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.

Cellular immune responses to Neisseria meningitidis in children

There is an urgent need for effective vaccines against serogroup B Neisseria meningitidis. Current experimental vaccines based on the outer membrane proteins (OMPs) of this organism provide a measure of protection in older children but have been ineffective in infants. We postulated that the inability of OMP vaccines to protect infants might be due to age-dependent defects in cellular immunity. We measured proliferation and in vitro production of gamma interferon (IFN-gamma), tumor necrosis factor alpha, and interleukin-10 (IL-10) in response to meningococcal antigens by peripheral blood mononuclear cells (PBMCs) from children convalescing from meningococcal disease and from controls. After meningococcal infection, the balance of cytokine production by PBMCs from the youngest children was skewed towards a TH1 response (low IL-10/IFN-gamma ratio), while older children produced more TH2 cytokine (higher IL-10/IFN-gamma ratio). There was a trend to higher proliferative responses by PBMCs from older children. These responses were not influenced by the presence or subtype of class 1 (PorA) OMP or by the presence of class 2/3 (PorB) or class 4 OMP. Even young infants might be expected to develop adequate cellular immune responses to serogroup B N. meningitidis vaccines if a vaccine preparation can be formulated to mimic the immune stimulus of invasive disease, which may include stimulation of TH2 cytokine production.

Aberrant CD3- and CD28-Mediated Signaling Events in Cord Blood T Cells Are Associated with Dysfunctional Regulation of Fas Ligand-Mediated Cytotoxicity

There have been numerous reports of decreased acute and chronic graft-vs-host disease (GVHD) in patients receiving HLA-matched or HLA-disparate umbilical cord transplants. However, little is known about the mechanisms underlying the low incidence of GVHD in umbilical cord blood transplantation (CBT). In this study, we examined CD3- and CD28-mediated functional properties and signaling events in CB T cells (CBTCs). Dual stimulation of peripheral blood TCs (PBTCs) and bone marrow TCs (BMTCs) with mAbs to CD3- and CD28-induced expressions of Fas ligand (FasL), as well as CD25 and CD154 (CD40L), whereas defective induction of these activation-associated cell surface molecules were observed in CBTCs. Engagement of both CD3 and CD28 induced FasL-mediated cytotoxicity in peripheral blood TCs (PBTCs) but not CBTCs; however, both of these tissue sources possess intrinsically similar proliferative responsiveness. Analysis of CD3- and CD28-induced signal transduction revealed a deficiency in signaling events that involved repressed tyrosine phosphorylation and enzymatic activities of a family of mitogen-activated protein kinases, extracellular signal-regulated kinase 2, stress-activated protein kinase/c-jun N-terminal kinase (SAPK/JNK), and p38mapk, as well as p56lck and ZAP-70 in CBTCs compared with those in PBTCs. These results suggest that CD3- and CD28-mediated signaling events blockage in CBTCs may be responsible for dysfunction of FasL-mediated cytotoxicity and lead to the low incidence of severe GVHD in CBT.

Postthymic Development of CD28−CD8+ T Cell Subset: Age-Associated Expansion and Shift from Memory to Naive Phenotype

During human aging, one of the major changes in the T cell repertoire is a dramatic expansion of T cells with the atypical CD28−CD8+ phenotype. In this study, we show that this increase is a consequence not only of an expansion in the CD28−CD8+ population but also of a decrease in the number of CD28+CD8+ T cells. The decrease in circulating CD28+CD8+ T cells is dramatically accelerated after the age of 50 and is not accompanied by an equivalent reduction in the CD28+CD4+ subset. Our findings confirm that aging leads to an accumulation of CD45RO+ T cells within the CD28+CD8+ subset as previously observed. Surprisingly, we found an increase in CD45RA+ expression with age in the CD28−CD8+ subset. Immune-phenotyping for activation markers, measurement of telomere DNA content, and cytokine production analysis indicate that the large majority of CD28−CD8+ T cells are Ag-experienced, despite their CD45RA+ phenotype. Our study further demonstrates that the poor proliferative response displayed by CD28−CD8+ T cells is not a consequence of telomere shortening. Also, analysis of cytokine production at the single cell level revealed that the proportions of IFN-γ+, IL-4+, and IL-10+ T cells are considerably higher among the CD28−CD8+ than the CD28+CD8+ subset. In summary, these data explain the presence of CD45RA+ T cells in the elderly, shed light on the phylogenetic origin of CD28−CD8+ T cells, and suggest a role for these cells in the immune senescence process.

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.

Analysis of the cord blood T lymphocyte response to superantigen

We have characterized the T lymphocyte population of the human neonate in respect of the expression of phenotypic profiles for naive, memory and differentiated populations. We have examined the response of the neonate T cell to the superantigen Staphylococcus enterotoxin B (SEB) and compared the response to T cells from healthy adults. We found that the primary response to SEB is equivalent in neonates and adults but that the secondary response demonstrates hyporesponsiveness in the neonate that is more profound than in adults. This response was associated with increased expression of CD25; the alpha chain of the IL-2 receptor, equivalent to that seen in responding cells from adults. A modest increased expression of CD122 and CD132, the beta and gamma chains of the IL-2 receptor, was also observed. There was no increase in the IL-4 receptor (CD124). The hyporesponsive neonate T cells proliferated in response to exogenous IL-2 but the response was less than none SEB treated cells. The neonate cells did not respond to IL-4. We also examined the expression of MHC class II molecules on SEB stimulated cells and found that both neonate and adult T cells upregulate MHC class II to a similar degree. The difference in the hyporesponsive cells appears to result in part from a lower production of IL-2 and in part from a lower ability of cord cells to respond to IL-2. Since the stimulated cord cells expressed IL-2 receptor at the same levels as similarly treated adult cells; there may be differences in down stream signaling pathways.

The locus of tumor necrosis factor-alpha action in lung inflammation

The pulmonary host response to infection and inflammation appears, at least in part, to be compartmentalized from the systemic host response. Tumor necrosis factor-alpha (TNF-alpha) has been implicated in lung inflammation and injury, but its site(s) of action has not been clearly defined. To investigate this, transgenic mice (surfactant apoprotein C promotor/soluble TNF receptor type II-Fc fusion protein ([SPCTNFRIIFc] mice) were generated in which TNF-alpha was selectively antagonized in the distal lung through tissue-specific expression of sTNFRIIFc, a soluble TNF inhibitor. The lung inflammatory response in these mice to pulmonary challenge with Micropolyspora faeni antigen or lipopolysaccharide (LPS) was compared with the response of wild-type mice, wild-type mice treated with recombinant sTNFRIIFc intravenously, and type I TNF-receptor knockout mice. Recruitment of polymorphonuclear leukocytes (PMN) to the lung after challenge with M. faeni antigen was essentially abolished in the TNFRI knockout mice and markedly reduced in the SPCTNFRIIFc mice. Wild-type mice given sTNFRIIFc intravenously in amounts resulting in lung concentrations similar to those in SPCTNFRIIFc mice also showed significantly reduced lung PMN recruitment, whereas those given doses that achieved such concentrations in the blood but low levels in the lung did not. In contrast, PMN recruitment to the lung following aerosol challenge with LPS was reduced significantly in the TNFRI knockout mice and in mice given high-dose sTNFRIIFc intravenously, but was not reduced significantly in SPCTNFRIIFc mice. Thus, inhibition of PMN recruitment in response to M. faeni antigen correlated largely with the extent of intrapulmonary inhibition of TNF-alpha, whereas the response to LPS correlated best with the extent of extrapulmonary inhibition of TNF-alpha. These studies indicate that TNF-alpha may act at different loci to mediate lung inflammation, with the site of action depending in part on the nature of the inflammatory stimulus, and that SPCTNFRIIFc mice provide a tool by which the locus of TNF action can be addressed.

Unique profile of IL-4 and IFN-gamma production by peripheral blood mononuclear cells in infants with atopic dermatitis

Although the level of house dust mite (HDM)-specific lymphocyte proliferation is high in infants with atopic dermatitis (AD), the level of HDM-specific IgE antibody (HDM-IgE-RAST) is usually very low or negative. To elucidate the cause of the deficient HDM-specific IgE antibody formation in infants with AD, we examined the profile of IL-4 and IFN-gamma production by HDM-stimulated PBMCs. The amount of IL-4 production was higher in infants with AD and in children with AD (3 to 15 years) than in the nonatopic control subjects. Although the amount of IFN-gamma production in children with AD was lower than that found in nonatopic children, it was higher in infants with AD than in nonatopic infants. This result suggests that HDM-specific helper T lymphocytes in infants with AD have not yet differentiated into TH2 but rather stayed at the stage of TH0. The level of IgE-RAST for egg white (EW) is already elevated in infants with AD. The amount of IL-4 produced by EW-stimulated PBMCs was comparable to that produced by HDM-stimulated PBMCs in infants with AD. However, the amount of IFN-gamma produced by EW-stimulated PBMCs was distinctly lower than that produced by HDM-stimulated PBMCs in infants with AD. Although there was no correlation between the amount of IL-4 production by HDM-stimulated PBMCs and the level of HDM-IgE-RAST in infants with AD, the amount of IL-4 production by EW-stimulated PBMCs was closely correlated with the level of EW-IgE-RAST. These results suggest that it is not the lack of IL-4 but rather a relative increase in IFN-gamma production by HDM-specific helper T lymphocytes that causes the deficiency of HDM-specific IgE-antibody synthesis in infants with AD.

Low CD3+CD28-induced interleukin-2 production correlates with decreased reactive oxygen intermediate formation in neonatal T cells

The capacity of neonatal T cells to secrete interleukin-2 (IL-2) has been reported to be variable. We analysed IL-2 production in purified neonatal and adult T cells using polyclonal activator phorbol ester + calcium ionophore (PDBu + iono) or receptor-mediated anti-CD3/anti-CD3+ anti-CD28 stimulation. PDBu + iono induced equally high IL-2 levels in both groups and, when stimulated with plate-bound anti-CD3 monoclonal antibody (mAb), the IL-2 secretion by neonatal cells was undetectable and adult cells produced low amounts of IL-2 (mean 331 +/- 86 pg/ml). The addition of anti-CD28 mAb to anti-CD3-stimulated cells markedly increased IL-2 production in both cell types, but levels of IL-2 in neonatal T cells remained clearly lower than those of adult T cells (respective mean values: 385 +/- 109 pg/ml and 4494 +/- 1199 pg/ml). As NF-kappa B is a critical transcription factor in the control of IL-2 expression, we next analysed its nuclear translocation in neonatal and adult T cells using the electrophoretic mobility shift assay and, because induction of reactive oxygen intermediates (ROI) is required for the activation of NF-kappa B, we also analysed levels of intracellular ROI in these cells using the ROI-reactive fluorochrome DCFH-DA and flow cytometry. In neonatal T cells NF-kappa B activation and ROI formation after anti-CD3 stimulation were low compared with adult T cells and, although addition of anti-CD28 mAb increased induction of NF-kappa B and ROI formation, levels similar to those of adults were not achieved. After PDBu + iono stimulation, the cells showed similar ROI formation and IL-2 secretion. Our results suggest that reduced IL-2 production by neonatal T cells is specific for anti-CD3 and anti-CD3+ anti-CD28-mediated stimulation and that these activators cannot effectively activate the ROI-NF-kappa B signalling pathway in neonatal T cells.

Interleukin (IL)-15 enhances antibody-dependent cellular cytotoxicity and natural killer activity in neonatal cells

Interleukin (IL)-15 is a novel cytokine that is very similar to IL-2 in receptor specificity and biological activities. We compared the ability of IL-15 and IL-12 to enhance the cytotoxicity of neonatal (cord blood) and adult mononuclear cells (MNC) in both natural killer (NK) and antibody-dependent cellular cytotoxicity (ADCC) assays. Incubation with IL-15 (10 ng/ml) or IL-12 (1 ng/ml) for 18 h enhanced the NK activity (using K562 target cells) of both cord and adult MNC, increasing cord cell cytotoxicity threefold. Similar enhancement was seen in ADCC assays using erythrocyte targets and NK-resistant CEM cells coated with HIV gp-120 antigen. Incubation of cord cells with IL-15 or IL-12 for 1 week increased both NK and ADCC, although the combination produced less of an effect than either cytokine alone. IL-15 also increased the percentage of CD16+/CD56+ cells after 1 week incubation. This enhancement of NK and ADCC activities and the number of NK cells by IL-15 suggests it may be clinically useful in treating immunodeficient patients.

Differential cytokine regulation of natural killer cell-mediated necrotic and apoptotic cytotoxicity

Natural killer (NK) cells can kill target cells by either necrotic or apoptotic mechanisms. Using the 51Cr-release assay to measure necrotic death of target cells, neonatal NK cells had low NK activity (K562 targets) and high lymphokine-activated killer (LAK) activity (Daudi targets) compared with adult cells, as has been previously reported. Using a 125I-deoxyuridine (125I-UdR) release assay, cord cells were shown to also have higher apoptotic LAK activity against YAC-1 target cells. Interleukin-4 (IL-4) inhibited interleukin-2 (IL-2)-induced necrotic killing of target cells by adult effectors but had no such inhibitory effect on cord cells. In contrast, IL-4 inhibited both adult and cord LAK cytotoxicity of YAC-1 target cells by apoptotic mechanisms with higher suppression observed in cord cell preparations. Using a colorimetric substrate conversion assay, IL-2 induced higher, and IL-4 had a more significant suppressive effect on, cord cell granzyme B enzyme activity compared with adult cells, paralleling apoptosis cytotoxicity data. Co-culture of either adult or cord LAK cells with IL-4 had a similar inhibitory effect on granzyme B protein expression, as detected by Western blotting. In contrast, IL-4 did not inhibit perforin expression, thereby defining IL-4 as a cytokine that can differentially regulate the NK cell-mediated cytotoxicity processes of apoptosis and necrosis. The differential sensitivity of cord cells to cytokine regulation of cytotoxicity may also have implications for cord blood transplantations, as NK cells are known to function as an effector cell in both graft-versus-host disease and in the graft-versus-leukaemia phenomena.

Cord blood mononuclear cells and milk-specific T-cell clones are tools to evaluate the residual immunogenicity of hydrolyzed milk formulas

BACKGROUND

Hydrolyzed milk formulas (HFs) are given to infants allergic to cow's milk proteins and, for preventive reasons, to atopy-prone newborns for which breast feeding is not feasible. The ultimate properties of HFs are not only a reduced allergenicity but also decreased immunogenic capacity combined with good taste and caloric value. No information is available concerning the capacity of HFs to induce immune responses.

OBJECTIVE

We sought to determine the residual immunogenic capacity of partially (pHF) and extensively hydrolyzed milk formula (eHF), and we studied the cellular reactivity of cord blood-derived (n = 71) mononuclear cells induced by 10 different HFs.

METHODS

To test the effect of HF on T-helper cells, beta-casein-specific T-cell clones (TCCs, n = 21) from individuals allergic to milk were established, and T-cell proliferation and cytokine profiles (interferon-gamma and IL-4) were determined on stimulation with HF.

RESULTS

We found significantly reduced proliferative responses of eHF compared with milk proteins. Whey-based pHF displayed the same proliferative capacity as unmodified milk proteins. As expected, extensively processed whey products displayed lower cellular responses compared with partially hydrolyzed products (pHF whey vs eHF whey, p < 0.0001). No difference in cellular response was found between casein-based pHF and casein-based eHF. Beta-casein-specific TCCs (n = 21) proliferated in response to casein-derived hydrolysates (14% with casein/whey-based pHF, 4% with casein-based pHF, and 0% with casein-based eHF). Whey-based pHF was also found to induce proliferation in beta-casein-specific TCCs, indicating the presence or the generation of peptides displaying cross-reactivity with these whey-derived hydrolysates. TCCs stimulated with whey- or casein-based pHF or eHF produced the same amount of cytokines (IL-4, interferon-gamma) as the same clones stimulated with unmodified products.

CONCLUSION

Our data indicate that whey- and casein-derived eHFs display highly reduced immunogenic properties at the T-cell level. In contrast, pHFs display residual immunogenic properties detectable at the T-cell level, reflecting a potential for the induction of pathogenetically important T-cell responses.

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.

Evolution of immunologic functions of the mammary gland and the postnatal development of immunity

Physiologic delays in production of immune factors occur in mammals including Homo sapiens. This finding is counter to a basic tenet of biologic evolution, because such delays increase the risk of infections. The disadvantage is, however, offset by defense factors in milk of the species in whom the developmental delay occurs. Reciprocal relationships between the production of immune factors by the lactating mammary gland and the production of those defense agents during early infancy are found in all investigated mammalian species. Thus, the evolution of these processes is closely related. Certain immunologic components of milk are highly conserved, whereas others vary according to the species. The variations most likely evolved by genetic mutations and natural selection. In addition, the immune composition of mammalian milks is associated with developmental delays in the same immunologic agents. Furthermore, most closely related mammals, such as humans and chimpanzees, are most similar in the defense agents in their milks and the corresponding developmental delays in their immune systems. Defense factors in human milk include antimicrobial agents (secretory IgA, lactoferrin, lysozyme, glycoconjugates, oligosaccharides, and digestive products of milk lipids), antiinflammatory factors (antioxidants, epithelial growth factors, cellular protective agents, and enzymes that degrade mediators of inflammation), immunomodulators (nucleotides, cytokines, and antiidiotypic antibodies), and leukocytes (neutrophils, macrophages, and lymphocytes). Because of a lack of geographic/ethnic variation in the immunologic composition of human milk and corresponding immunologic delays in infants, these evolutionary processes seem stable. This is supported by investigations of diverse populations that indicate that this evolutionary outcome is highly beneficial to human infants.

Enhancement of antibody-dependent cellular cytotoxicity of neonatal cells by interleukin-2 (IL-2) and IL-12

Newborn infants are more susceptible to infections due in part to deficiencies in the cytotoxic functions of their lymphocytes. We investigated the ability of interleukin-2 (IL-2) and IL-12 to enhance the cytotoxicity of neonatal (cord blood) and adult mononuclear cells (MNCs) in both natural killer (NK) cell and antibody-dependent cellular cytotoxicity (ADCC) assays. The cytotoxic activity of cord blood MNCs was less than 50% that of adult MNCs in most assays prior to exposure to cytokines. Incubation with IL-2 (100 U/ml) or IL-12 (1 ng/ml) for 18 h increased the NK cell activity (using K562 target cells) of both cord blood and adult MNCs, and the combination of IL-2 and IL-12 increased cord blood cytotoxicity threefold, making the cytotoxicity of cord blood cells equivalent to that of adult cells treated with the same cytokines. In ADCC assays with chicken erythrocyte targets, the combination of IL-2 and IL-12 increased the cytotoxicities of both cord blood and adult MNCs, with greater enhancement again seen with cord blood cells. In assays with NK cell-resistant CEM cells coated with human immunodeficiency virus (HV) gp120 antigen in the presence of hyperimmune anti-HIV immunoglobulin, ADCC of cord blood MNCs was about 50% that of adult MNCs; ADCC of cord blood MNCs increased two- to threefold with the addition of IL-2 and IL-12, whereas ADCC of adult MNCs did not increase. Incubation of cord blood cells, but not adult cells, with IL-2 or IL-12 for 1 week increased the percentage of CD16+/CD56+ cells two- to fivefold and enhanced ADCC activity. Thus, IL-2 and IL-12 greatly enhance both the NK cell and ADCC activities of neonatal MNCs and increase the number of NK cells in longer-term culture.

Postnatal changes in mucosal immune response: a physiological perspective of breast feeding and weaning

There are profound changes of immune activity during infancy from suppression during breast feeding, activation with weaning, and later intrinsic down-regulation after weaning. Breast feeding, as well as protecting against infections, seems to have a fundamental role in modifying the immune system against certain disease states. Transforming growth factor (TGF)beta in breast milk may mediate this immunosuppressive effect. Although the infant immune system is not in an adult state, the notion that the infant immune system is immature is difficult to reconcile with evidence that most infants respond appropriately to immunization and to infections. The systemic immune system of neonates may be subject to Th2 immune deviation, while the mucosal immune system, particularly of the gastrointestinal tract and probably the respiratory tract, is up-regulated with physiological inflammation during infancy. Weaning is associated with a peak of intestinal immune activation which includes mucosal mast cells and T cells. The physiological effects of this activation are promotion of epithelial growth of the small intestine and initial activation of mechanisms leading to subsequent down-regulation of the physiological heightened immune activity. This coincides with the development of mucosal (oral) tolerance to food and bacterial antigens.

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.

Cytokine production differs in children and adults

The susceptibility of normal, healthy children to infection has long been recognized, but the underlying mechanisms are poorly understood. As adequate cytokine production is crucial for optimal immune responses, we assessed antigen and mitogen-induced cytokine production in healthy children. Our results demonstrate that healthy children differ markedly compared with adults in their ability to produce cytokines (IL-2, interferon-gamma, IL-4, and IL-6). Maximal stimulation with mitogen demonstrated impaired cytokine production with markedly lower levels of all four cytokines produced compared with adult levels. When stimulated with antigens, median levels of IL-2 and IL-4 remained lower than adult values, IL-6 production was increased as was interferon-gamma, albeit not significantly. Although the study was carried out on peripheral blood mononuclear cells that represent a restricted compartment of the immune system, these data suggest that, in healthy children, cytokine production is decreased and/or altered and could result in a suboptimal immune response, which could be one of the factors underlying increased susceptibility to infection in children.

Function and phenotype of immature CD4+ lymphocytes in healthy infants and early lymphocyte activation in uninfected infants of human immunodeficiency virus-infected mothers

The function and phenotypes of CD4+ lymphocytes in infants are different than in adults and are modulated by maturational changes and exposure to environmental antigens. Infants of non-human immunodeficiency virus (HIV)-infected mothers and uninfected infants of HIV-infected mothers, 0 to 6 months of age, were examined for CD4+ lymphocyte function by in vitro interleukin-2 (IL-2) production and for CD4+ phenotypes by three-color flow cytometry. A minority of these uninfected infants (28%) had functional responses similar to those of healthy adult women (IL-2 production in response to anti-CD3, alloantigen, and mitogen), while the remainder were capable of responding to alloantigen and mitogen but not to anti-CD3. We did demonstrate reduced phytohemagglutinin-stimulated IL-2 production in uninfected infants born to HIV-seropositive mothers compared to that in infants from seronegative mothers. The proportions of CD3+ CD4+, CD4+ HLA-DR- CD38+, and CD4+ CD45RA+ RO- (naive) lymphocytes were much higher in infants than in adults, and the proportions of CD4+ CD45RA- RO+ (memory) and CD4+ CD25+ (IL-2 receptor-bearing) lymphocytes were lower in infants than in adults. The proportions of activated (CD4+ HLA-DR+ CD38+) and memory (CD4+ CD45RA- RO+) lymphocytes were increased in uninfected infants of HIV-infected mothers compared to infants of uninfected mothers. Therefore, T-helper-cell function is immature in many infants, but the CD4+ lymphocytes of some HIV-exposed, uninfected infants have been stimulated by antigen at an early age.

High level interleukin-12 production, but diminished interferon-gamma production, by cord blood mononuclear cells

Cell-mediated immunity (CMI) in neonates is relatively deficient when compared with adults. Defects in cytokine production and/or regulation may contribute to heightened susceptibility to infection by intracellular pathogens. The heterodimeric cytokine IL-12 is a key regulator of CMI and inducer of interferon-gamma (IFN-gamma) production. We report here that umbilical cord blood-derived mononuclear cells (MNC) are capable of producing IL-12 (p40 subunit, measured by RIA, and IL-12 p70 heterodimer, by ELISA) at levels comparable to or greater than adult peripheral blood MNC, after stimulation with heat-killed Staphylococcus aureus in 18-h cultures. As in adult MNC, S. aureus induced IL-12 p40 mRNA accumulation in cord blood MNC. IFN-gamma was also produced in the S. aureus-stimulated cultures, in an IL-12-dependent manner, but cord blood MNC produced 5-fold lower levels of IFN-gamma compared with adult MNC (p < 0.05). Preincubation with IL-10 inhibited IL-12 p40 production by cord blood and adult peripheral blood MNC in a dose-dependent fashion, whereas neutralization of endogenous IL-10 enhanced IL-12 and IFN-gamma levels. The results demonstrate that the relative CMI deficiency in neonates is not due to an intrinsic defect in the capacity of neonatal MNC to produce IL-12. The underlying factors responsible for diminished IFN-gamma production are not known, but may lie in the balance of stimulatory and inhibitory signals delivered to the IFN-gamma secreting cells along with IL-12, or may relate more to the absence of memory T cells among cord blood MNC.

Neonatal sepsis: pathogenesis and supportive therapy

Bacterial infections remain an important cause of neonatal mortality and morbidity. Pathogenesis of the neonate's predilection to infection are multifactorial. Factors directly attributable to the infant include humoral, phagocytic, and cellular deficiencies. Septic neonates may have reduced neutrophil storage pools that cause profound neutropenia. Both correlate with poor prognosis. Antibiotic administration is mandatory in neonatal sepsis. Supplementary treatments may be useful. Granulocyte transfusions, when available, provide neutrophils, improving the neonate's neutrophil count and neutrophil function. The efficacy of intravenous immunoglobulin (i.v.IG) is questionable because the prophylactic and therapeutic administration of i.v.IG fails to reduce the incidence of bacterial infections or affect the overall survival rate. Hyperimmune preparations seem to be more effective. The administration of granulocyte colony-stimulating factor induces myeloid progenitor proliferation, enhances the neutrophil storage pool, produces neutrophilia, and improves neutrophil function. More extensive, well-designed, and carefully control trials are needed to determine the benefit of supportive therapies for neonatal sepsis.

Prenatal origins of asthma and allergy

The prevalence of asthma and related allergic disorders has increased considerably over the last 25 years. Genetic stock has not changed, so environmental factors must have influenced the phenotype. Infants who develop allergy already have an altered immune response at birth. We have investigated the development of immune responses during gestation and the effect of maternal allergen exposure during pregnancy and infant exposure in the first month of life on the development of allergy and disease. There was higher specific peripheral blood mononuclear cell proliferation to house dust mite (P = 0.01) and birch pollen (P = 0.004) in the third trimester compared with the second trimester, with the first positive responses seen at 22 weeks gestation. Maternal exposure to birch pollen after 22 weeks resulted in higher (P = 0.005) infant peripheral blood mononuclear cell responses to birch pollen at birth. Infants born at term, with at least one atopic, asthmatic parent, who developed allergic symptoms and positive skin prick test by one year of age had raised proliferative responses to house dust mites at birth compared to those with no symptoms (P = 0.01). In genetically predisposed individuals, antenatal factors, including maternal and thereby fetal exposure to allergens and maternoplacental-fetal immunological interactions, are active in determining whether an allergic predisposition is manifested as disease.

The proximal regulatory element of the interferon-gamma promoter mediates selective expression in T cells

Interferon-gamma (IFN-gamma) is produced by natural killer cells and certain subsets of T cells, but the basis for its selective expression is unknown. Within the region between -108 and -40 base pairs of the IFN-gamma promoter are two conserved and essential regulatory elements, which confer activation-specific expression in T cells. This report describes studies indicating that the most proximal of these two regulatory elements is an important determinant of its restricted expression. The proximal element is a composite site that binds members of the CREB/ATF, AP-1, and octamer families of transcription factors. Jun is essential for activation-induced transcription and binds preferably as a heterodimer with ATF-2. In contrast, CREB appears to dampen transcription from this element. The CpG dinucleotide in this element is selectively methylated in Th2 T cells and other cells that do not express IFN-gamma, and methylation markedly reduces transcription factor binding. As a target for DNA methylation and for binding of transcription factors that mediate or impede transcription, this element appears to play a central role in controlling IFN-gamma expression.

Development of immune functions related to allergic mechanisms in young children

The newborn immune system differs quantitatively and functionally from that of adults. Development of the immune system has important implications for childhood diseases. The immaturity of the immune system in the first years of life may contribute to failure of tolerance induction and in the development of allergic disease. T cell function is diminished, especially the capacity to produce cytokines; production of interferon (IFN)-gamma, and IL-4 is strongly reduced. IFN-gamma has been found to be even lower in cord blood of newborns with a family history of atopy. Differences in other cell types (natural killer cells, antigen-presenting cells, and B cells) could also play a role in the development of allergic disease. Current data suggest that irregularities in IgE synthesis, helper T cell subsets (Th1, Th2, CD45RA, and CD45RO), cytokines (IL-4, IFN-gamma), and possibly other cell types may play a role in the development of allergy in childhood. Moreover, the role of cell surface molecules, like co-stimulatory molecules (CD28, CD40L), activation markers (CD25), and adhesion molecules (LFA-1/ICAM-1, VLA-4/ VCAM-1) is also discussed. These variables are modulated by genetic (relevant loci are identified on chromosome 5q, 11q, and 14) and environmental forces (allergen exposure, viral infections, and smoke). The low sensitivity of current predictive factors for the development of allergic diseases, such as cord blood IgE levels, improves in combination with family history and by measurement of in vitro responses of lymphocytes and skin reactivity to allergens. New therapeutic approaches are being considered on the basis of our current understanding of the immunopathology of allergic disease, for instance cytokine therapy and vaccination with tolerizing doses of allergen or peptides.

Reproductive effects of chronic administration of murine interferon-gamma

Daily subcutaneous doses of 0.02, 0.2, or 2 mg/kg/d of recombinant murine interferon-gamma (rmuIFN-gamma) were given to mice on postnatal days 8 through 60 to determine effects on maturation, behavioral/ functional development, and reproductive capacity. Male mice receiving 2 mg/kg/d rmuIFN-gamma had delayed sexual maturation, reduced epididymal and testes weights, reduced sperm count and concentration, and sperm abnormalities (crimped flagellum). Mating performance and fertility were also reduced in the absence of altered histopathology of the testes. Males given 0.2 and 2 mg/kg/d had swelling and ulcerative dermatitis around the urogenital area, which were observed after sexual contact and attributed to a bacterial infection. Motor activity (time spent in movement) was decreased in all mice receiving 2 mg/kg/d. No microscopic changes observed in any organs were attributed to rmuIFN-gamma administration.

Decreased interleukin-10 production by neonatal monocytes and T cells: relationship to decreased production and expression of tumor necrosis factor-alpha and its receptors

The production of IL-10 by human neonatal blood mononuclear leukocytes (BML) stimulated with lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha), antibodies to CD3, or phorbol 12-myristate 13-acetate (PMA) was measured. The production of IL-10 by neonatal BML cultured with LPS or TNF-alpha was approximately 20 and approximately 15%, respectively, of adult BML. The combination of human recombinant TNF-alpha and LPS failed to augment IL-10 production in neonatal BML. The decreased production of IL-10 by neonatal leukocytes was not due to an autocrine feedback mechanism because only low concentrations of IL-10 were found in newborn sera. A connection with TNF-alpha could not be ruled out, because TNF-alpha production by LPS-stimulated newborn BML and the expression of TNF-alpha receptors on newborn monocytes were reduced. Mean +/- SD of concentrations of IL-10 in supernatants from adult and neonatal BML after stimulation with antibodies to human CD3 for 48 or 72 h were 914 +/- 386 and 178 +/- 176 pg/mL, respectively (p < 0.0001). In experiments with enriched populations of neonatal T cells, the addition of PMA failed to augment IL-10 production. This suggested that newborn T cells may be in a different state of activation than adult T cells Thus, IL-10 production in neonatal monocytes and T cells is reduced and this study suggests that the reduction may be secondary in part to regulatory processes involving TNF-alpha and its receptors.

Role of gamma interferon in a neonatal mouse model of group B streptococcal disease

The aim of this study was to assess the role of gamma interferon (IFN-gamma) in a neonatal mouse model of group B streptococcal (GBS) sepsis. IFN-gamma was produced by spleen cells at 24, 48, and 72 h after GBS challenge. Treatment with anti-IFN-gamma at 6 h before challenge totally abrogated the IFN-gamma response but did not affect survival. Subcutaneous administration of recombinant IFN-gamma (2,500 IU per pup) at 18 h after challenge resulted in increased survival time and reduced blood colony counts at 48 and 72 h. In vitro preincubation of neonatal whole blood with IFN-gamma before the addition of GBS resulted in significant restriction of bacterial growth. These data indicate that administration of recombinant IFN-gamma can partially restore impaired host defenses against GBS in neonatal mice. This cytokine may be useful for the treatment of neonatal infections.

Brucella abortus conjugated with a peptide derived from the V3 loop of human immunodeficiency virus (HIV) type 1 induces HIV-specific cytotoxic T-cell responses in normal and in CD4+ cell-depleted BALB/c mice

We have previously shown that immunization of mice with human immunodeficiency virus (HIV)-derived proteins or peptides conjugated to inactivated Brucella abortus induces the secretion of virus-neutralizing antibodies, predominantly of the immunoglobulin G2a (IgG2a) isotype. In addition, B. abortus activates human CD4+ and CD8+ cells to secrete gamma interferon. Since these are both characteristics of a Th1-type immune response, which is associated with the development of cell-mediated immunity, it was important to determine if B. abortus conjugates would also act as a carrier to induce a cytotoxic T-lymphocyte (CTL) response. To test this hypothesis, we conjugated an 18-amino-acid peptide from the V3 loop of the MN strain of HIV-1 gp120 that contains both B- and cytotoxic T-cell epitopes to B. abortus (B. abortus-MN 18-mer). A 10-amino-acid fragment of this peptide has been shown to be the minimal CTL determinant presented by murine H-2Dd. It was found that two in vivo immunizations with 10(8) organisms of B. abortus-MN 18-mer followed by in vitro stimulation with peptide induced a virus-specific CTL response. Conjugation to B. abortus was required for in vivo priming, since there was no induction of memory CTLs when B. abortus was only mixed with peptide. Targets pulsed with peptide as well as those infected with a vaccinia virus encoding HIV gp160 were killed, demonstrating recognition of naturally processed envelope. Also, major histocompatibility complex-incompatible L cells which were infected with vaccinia viruses that encoded H-2Dd, but not H-2Kd, and pulsed with peptide were lysed. This demonstrated the appropriate major histocompatibility complex class I restriction. Treatment of the mice with anti-L3T4 prior to immunization caused a severe depletion of CD4+ lymphocytes, yet it did not decrease the CTL priming. Thus, inactivated B. abortus can induce non-CD4+ cells to produce the cytokines required for CTL induction. We conclude that B. abortus stimulates a cellular as well as a humoral immune response, even in the relative absence of CD4+ helper cells. It may be a particularly useful vaccine carrier in HIV-1-infected individuals or others with impaired CD4+ T-cell function.

Role of interleukin-2 and interferon-gamma in inducing production of IgG subclasses in lymphocytes of human newborns

Unlike lymphocytes from adults, lymphocytes from cord blood of neonates cannot synthesize immunoglobulin G (IgG) in response to pokeweed mitogen (PWM). By using this mitogen in concert with interferon-gamma (IFN-gamma), interleukin-2 (IL-2), or interleukin-6 (IL-6), we studied the induction of IgG subclass molecules in lymphocytes of human neonates. IFN-gamma induced a limited, but substantial, enhancement of IgG2 production by neonatal lymphocytes. IL-2 dose dependently increased the production of each neonatal IgG subclass, whereas IL-6 did not. However, in adult lymphocytes, and under specific conditions, IL-6 or IL-2 each increased the production of all four IgG subclasses. Early in the culture IFN-gamma synergized with IL-2 during the latter or whole culture period to enhance cord blood IgG2 levels. This finding contrasted with the adult IgG2 synthesis synergistically up-regulated by IFN-gamma and IL-6. IL-2 caused a graded increase in immunoglobulin production in neonatal lymphocytes with IgG3 being the highest and IgG2 the lowest, thus corresponding to the differential increase of serum levels of IgG3/IgG1 and IgG4/IgG2 early in childhood. Results suggest that IL-2, but not IL-6, is critical to the development of human IgG subclass production.

Reduced primary antigen-specific T-cell precursor frequencies in neonates is associated with deficient interleukin-2 production

Clinical evidence has indicated that the neonatal cell-mediated immune response to primary infection is delayed when compared to that of adults with the same primary infection. The mechanisms regulating the development of antigen-specific T-cell immunity in neonates remain to be elucidated. We examined the primary immune response to the non-recall antigen, keyhole limpet haemocyanin (KLH) in adults and neonates in vitro. We report here that conventional bulk culture methods show reduced proliferative responses in neonates although statistical significance was not achieved. Using limiting dilution analysis, the frequencies of KLH-specific T lymphocytes were 10-100-fold lower in neonates when compared to adults. Interleukin-2 (IL-2) production was significantly lower in the supernatants of neonatal mononuclear cells (MNC) stimulated with KLH when compared to adults. Addition of exogenous IL-2 increased precursor frequencies twofold in both adult and newborn cultures. In contrast to the secreted IL-2 levels, IL-2 mRNA expression was higher in antigen-stimulated neonatal MNC preparations, even though proliferation was lower. These observations indicate differential in vitro responsiveness in neonates and adults to primary antigenic challenge. Since no IL-2 was detected in cell lysates, the presence of high levels of IL-2 mRNA and low IL-2 production suggests inability by neonatal MNC to translate IL-2. This deficiency in IL-2 production may explain the reduced precursor frequencies, suggesting failure to recruit T lymphocytes in order to expand the KLH-specific T-cell response. These observations are important for the understanding of the development of primary immune responses and immunological maturation in neonates.

Interleukin-12 and tumor necrosis factor alpha mediate innate production of gamma interferon by group B Streptococcus-treated splenocytes of severe combined immunodeficiency mice

The existence of interleukin-12-mediated innate immune responses to group B streptococci (GBS) was tested by examining T-lymphocyte-independent gamma interferon (IFN) production in cultured splenocytes from severe combined immunodeficiency mice. Splenocytes were cultured with killed or living GBS for 48 h, and then IFN was measured by enzyme-linked immunosorbent assay. Type III GBS as well as other extracellular bacterial agents of neonatal sepsis (staphylococci and enterococci) induced IFN production, which was enhanced by interleukin-2 and was inhibited by neutralizing antibodies to tumor necrosis factor alpha and to mouse interleukin-12. Interleukin-12 bioactivity was present in conditioned medium from GBS-treated adherent macrophages. Adherent peritoneal macrophages and bone marrow-derived natural killer cells from severe combined immunodeficiency mice cultured separately with GBS did not produce IFN, whereas cocultures did produce IFN. Functional macrophage activation was evident by nitric oxide production in GBS-treated splenocyte cultures. The results show that extracellular pathogens such as GBS, similarly to intracellular microbes, induce macrophage interleukin-12 and tumor necrosis factor alpha, which promote natural killer cell secretion of IFN, which then enhances innate phagocyte resistance mechanisms.

Development of immune function in the intestine and its role in neonatal diseases

This review has traced the ontogeny of the human mucosal immune system, speculating that appropriate gut immune responses are essential in preventing many significant neonatal enteric diseases. Because the gastrointestinal tract serves as the portal of entry for many potential antigens, its mucosal immune function is essential in controlling antigenic responses and ensuring systemic tolerance. A thorough under standing of the development of the entire immune system is essential in defining intestinal mucosal immune function. From the protective barrier covering the enterocyte to the intraepithelial T lymphocytes, these components work together to limit antigen passage from the gut lumen to the underlying immune cells and, thus, promote normal immunity and tolerance. When abnormalities exist or when this immune barrier has not matured fully, conditions afflicting newborns, especially preterm infants, occur. Necrotizing enterocolitis, milk-protein enteropathy, and enteric bacterial infections are only three clinical examples of how aberrant gut immune-mediated defenses may have a significant role in their pathogenesis. In clinical practice, it is not only important to recognize these conditions at their onset but also to understand the basis for the underlying illness and identify newborns who are at an increased risk of acquiring them.

Inhibition of GM-CSF production by recombinant human interleukin-4: negative regulator of hematopoiesis

Interleukin-4 (IL-4), also known as B-cell stimulatory factor-1 (BSF-1), was initially identified as a T-cell product that mediates anti-IgM-induced DNA synthesis in B-lymphocytes. Various aspects of this highly pleiotropic cytokine have been described, including those on hematopoietic progenitor cells. However, the role of IL-4 in the hematopoietic system has been given different interpretations. Normal human hematopoietic progenitor cells do not proliferate under control of the autocrine system and cytokines are needed for proliferation and differentiation. However, IL-4 in itself does not support proliferation of these cells and if this is the case, the effects of IL-4 on hematopoietic progenitor cells still need to be investigated from the point of view of synergism with other cytokines as well as the control of accessory cells in the production of cytokines. We describe here some properties of IL-4 in association with cytokine production, with special emphasis on granulocyte-macrophage colony-stimulating factor (GM-CSF) production.

Interferon-gamma detection in cultures of newborn cells exposed to Listeria monocytogenes

Clearance of Listeria monocytogenes in experimental models of infection has underscored the importance of interferon-gamma (IFN-gamma) in host resistance to intracellular pathogens. Because L. monocytogenes infections are more severe in newborns than adults, we compared IFN-gamma accumulation in the supernatants of mononuclear cells infected in vitro from newborns with those from adults. Supernatants were assayed for IFN-gamma using an enzyme-linked immunosorbent assay. Uninfected newborn and adult mononuclear cells had less than 50 pg/ml of IFN-gamma at all times tested. IFN-gamma levels in supernatants from infected adult mononuclear cells at 24 h of culture (1.15 x 10(3) +/- 0.92 pg/ml) were greater than supernatants from infected newborn mononuclear cells (0.19 x 10(3) +/- 0.33 pg/ml). IFN-gamma concentrations in newborn cell cultures plateaued on day 3 of culture (1.6 x 10(3) +/- 1.1 pg/ml) and were not significantly less than concentrations from adult cells. However, adult cell IFN-gamma was further increased by day 5 (18.7 x 10(3) +/- 21.8 pg/ml). Because IFN-gamma plays a critical role in the host defense against L. monocytogenes, this delay in the release of IFN-gamma may be a factor in the increased susceptibility and severity of infection in the neonate.

Human peripheral blood CD4+ and CD8+ T cells express Th1-like cytokine mRNA and proteins following in vitro stimulation with heat-inactivated Brucella abortus

Defining the pattern of lymphokine production associated with Brucella abortus is critical for advancing the development of B. abortus as a vaccine carrier. In the present study we investigated the ability of heat-inactivated B. abortus or lipopolysaccharide from B. abortus to induce lymphokine production from purified human T cells in vitro. Gamma interferon (IFN-gamma), interleukin-2 (IL-2), IL-4, and IL-5 induction was assayed by mRNA-specific PCR and by enzyme-linked immunosorbent assay and bioassay for protein production. Following depletion of monocytes and B cells, B. abortus increased IFN-gamma and IL-2 mRNA expression in purified T cells compared with expression in unstimulated cells. In contrast, no IL-5 mRNA expression and only transient low-level IL-4 mRNA expression and no IL-4 protein secretion were detected. Phytohemagglutinin or phorbol myristate acetate plus ionomycin induced mRNA and protein for all these cytokines. Similar results were obtained with LPS purified from B. abortus. Removal of NK cells did not reduce lymphokine production, and enriched NK cells did not express IFN-gamma mRNA or secrete IFN-gamma protein in response to B. abortus, indicating that NK cells were not the responding population. Both CD4+ and CD8+ populations produced IFN-gamma and IL-2 in response to B. abortus. Preincubation of resting T cells with B. abortus or LPS from B. abortus for 7 days induced their differentiation into Th1-like cells as judged by their subsequent lymphokine response to phorbol myristate acetate plus ionomycin. These results suggest that B. abortus can induce differentiation of Th0 into Th1-type cells.

High numbers of autoantigen-reactive mononuclear cells expressing interferon-gamma (IFN-gamma), IL-4 and transforming growth factor-beta (TGF-beta) are present in cord blood

Umbilical cord blood of neonates and peripheral blood of healthy adults were analysed by in situ hybridization for numbers of mononuclear cells (MNC) expressing the cytokines IFN-gamma, TGF-beta and IL-4 mRNA without culture and after culture in the presence of acetylcholine receptor (AChR), myelin basic protein (MBP) and peripheral myelin protein P2. These antigens were chosen since they represent autoantigens in putatively immune-mediated neurological diseases. The numbers of cells expressing cytokine mRNA after 72 h culture in the presence of AChR, MBP and P2 were higher in cord blood than in peripheral blood of healthy adults. IFN-gamma, TGF-beta and IL-4 were always elevated in parallel. In cord blood there was a pronounced reactivity to several of the tested antigens, while such broad reactivity was not found in peripheral blood of healthy adults. No differences in cytokine mRNA expression were found between cord blood and peripheral blood of adults when cells were analysed without culture. The results show a capacity of cord blood cells to react to several autoantigens by the up-regulation of cytokine mRNA expression.

Differential effects of human immunodeficiency virus type 1 envelope protein gp120 on interferon production by mononuclear cells from adults and neonates

While considerable progress in examining the course of human immunodeficiency virus (HIV) infection in adults has been made, a better understanding of the natural history of perinatal HIV infection remains to be obtained. Dysregulation of the production and functions of various cytokines, especially the interferons (IFNs), during HIV infections has been reported. Using an in vitro model system, we examined the effects of the HIV type 1 envelope protein, gp120 (10, 50, and 100 ng/ml), on gamma IFN (IFN-gamma) and IFN-alpha production by lymphocytes from neonates and adults and also examined the potential regulatory effects of gp120 on phorbol 12-myristate acetate (PMA)- and Sendai virus-induced IFN-gamma and IFN-alpha production by lymphocytes. PMA at a concentration of 50 ng/ml plus 50 ng of calcium ionophore A23187 per ml was used to induce IFN-gamma, while 150 hemagglutinating units of Sendai virus was used to induce IFN-alpha production. The antiviral activity of both IFN-alpha and IFN-gamma in leukocyte culture supernatants was assayed on BG-9 cells by a dye uptake technique using vesicular stomatitis virus as a challenge virus. Placental cord blood leukocyte (CBL) samples from healthy, term infants and adult peripheral blood leukocytes (APBL) produced no IFN in response to gp120. However, CBL produced significantly decreased levels of IFN-gamma compared with APBL in response to PMA plus ionophore. gp120 significantly suppressed both Sendai virus-induced IFN-alpha and PMA-induced IFN-gamma production by both CBL and APBL in a dose-dependent manner. However, gp120-induced suppression of IFN-alpha and IFN-gamma was significantly greater with CBL than with APBL. Treatment of CBL and APBL with gp120 did not induce any phenotypic alteration of the CD45 RO+ subset. Increased suppression of IFN-alpha and IFN-gamma production by gp120 in neonates may partially explain their apparent increased susceptibility to the clinical progression of HIV infections compared with that of adults.

Interleukin-4 and interferon-gamma production in atopic and non-atopic children with asthma

Previous studies have demonstrated increased production of interleukin-4 (IL-4) and reduced production of interferon (IFN)-gamma in stimulated peripheral blood mononuclear cell cultures from children and adults with atopic dermatitis, however, it is unclear whether such an imbalance of cytokine production relates to other childhood atopic diseases such as asthma, and in particular to the presence of the atopic state per se. The production of IL-4 and IFN gamma in phytohaemagglutin- (PHA)-stimulated peripheral blood mononuclear cell (PBMC) cultures from atopic and non-atopic children with moderately severe chronic persistent asthma, and a group of age-matched non-atopic controls who did not have asthma was examined. Atopic children with asthma produced significantly more IL-4 and less IFN gamma than non-atopic children with asthma and non-atopic controls who did not have asthma. There was no significant difference in IL-4 or IFN gamma production between non-atopic children with asthma and controls. These findings demonstrate that an imbalance of IL-4 and IFN gamma production is present in atopic asthma as previously documented in atopic dermatitis, therefore suggesting that it is a feature of the atopic state per se.

Hypomethylation of the interferon-gamma gene correlates with its expression by primary T-lineage cells

To determine the potential role of methylation in the regulation of interferon-gamma (IFN-gamma) gene transcription by T cells, primary T-lineage cell populations were analyzed for the extent of methylation of three CpG sites within or near transcriptional activator elements in the 5' flank and first intron of the human IFN-gamma gene. A striking correlation was observed between the capacity of the IFN-gamma gene to be expressed and the degree of hypomethylation. The IFN-gamma gene was virtually completely methylated at all sites in thymocytes, neonatal T cells, and adult CD45RAhiCD45R0lo (antigenically naive) CD4 T cells, cell types that all have a low or undetectable capacity to express the IFN-gamma gene. In contrast, there was substantial hypomethylation in T-lineage cell types with relatively high capacities to express the IFN-gamma gene, including adult CD8 T cells and adult CD45RAloCD45R0hi (memory/effector) CD4 T cells. These results suggest that hypomethylation of the IFN-gamma genetic locus may be an important determinant of IFN-gamma gene expression in vivo by T-lineage cells.

Human cord blood mononuclear cells are preferentially infected by non-syncytium-inducing, macrophage-tropic human immunodeficiency virus type 1 isolates

Identification of the factors which impact on the transmission of human immunodeficiency virus type 1 (HIV-1) from an infected mother to her infant is essential for the development of effective strategies to prevent perinatal HIV-1 infection. The current study was designed to determine if unstimulated human neonatal cord blood mononuclear cells (CBMC) differ from adult peripheral blood mononuclear cells (PBMC) in susceptibility to HIV-1 infection. Both cell populations were challenged with two laboratory and two clinical HIV-1 isolates with different phenotypic properties. Infection was evaluated by quantitation of p24 antigen production and p24 antigen expression by an enzyme immunoassay and immunofluorescence, respectively. T-cell markers were determined by flow cytometry. Unstimulated CBMC were preferentially infected by macrophage-tropic, non-syncytium-inducing (non-SI) laboratory and clinical isolates, whereas PBMC were more susceptible to T-lymphotropic, SI HIV-1 strains. The macrophage-tropic strain HIV-1Ba-L replicated to 100-fold higher titers in CBMC than a similar inoculum of the SI isolate HIV-1LAI. The opposite occurred in unstimulated PBMC, which replicated HIVLAI to eightfold higher titers than the macrophage-tropic isolate. These findings indicate that a selection of viral phenotype may occur with unstimulated CBMC displaying a predominant susceptibility to infection by macrophage-tropic, non-SI HIV-1 strains and that this selection may influence mother-infant transmission of HIV-1.

Ontogeny of IL4 production

There is evidence to suggest that the production of some cytokines in childhood is different to that in adults. The production of IL4 in PHA-stimulated PBMC cultures was examined in healthy neonates, children and adults to determine the ontogeny of IL4 production throughout childhood. In vitro IL4 production was found to be significantly reduced in neonates and children under 10 years of age as compared to adults, and to increase progressively with age. The mechanisms leading to reduced IL4 production in neonates were shown to be different to those in children, with a defect in signal transduction demonstrated for lymphocytes from neonates but not children < 10 years. The presence of an inhibitory factor in cord blood plasma was also noted. These age-dependent variations in IL4 production and response to stimulation with PMA/Ca may reflect differences in naive and memory T cell populations.

CD28 activation promotes Th2 subset differentiation by human CD4+ cells

Ligation of CD28 provides a costimulatory signal to T cells necessary for their activation resulting in increased interleukin (IL)-2 production in vitro, but its role in IL-4 and other cytokine production and functional differentiation of T helper (Th) cells remains uncertain. We studied the pattern of cytokine production by highly purified human adult and neonatal CD4+ T cells activated with anti-CD3, phorbol 12-myristate 13-acetate (PMA) and ionomycin, or phytohemagglutinin (PHA) in the presence or absence of anti-CD28 in repetitive stimulation-rest cycles. Initial stimulation of CD4+ cells with anti-CD3 (or the mitogens PHA or PMA+ionomycin) and anti-CD28 monoclonal antibodies induced IL-4, IL-5 and interferon-gamma (IFN-gamma) production and augmented IL-2 production (6- to 11-fold) compared to cells stimulated with anti-CD3 or mitogen alone. The anti-CD28-induced cytokine production corresponded with augmented IL-4 and IL-5 mRNA levels suggesting increased gene expression and/or mRNA stabilization. Most striking, however, was the progressively enhanced IL-4 and IL-5 production and diminished IL-2 and IFN-gamma production with repetitive consecutive cycles of CD28 stimulation. The enhanced Th2-like response correlated with an increased frequency of IL-4-secreting cells; up to 70% of the cells produced IL-4 on the third round of stimulation compared to only 5% after the first stimulation as determined by ELISPOT. CD28 activation also promoted a Th2 response in naive neonatal CD4+ cells, indicating that Th cells are induced to express a Th2 response rather than preferential expansion of already established Th2-type cells. This CD28-mediated response was IL-4 independent, since enhanced IL-5 production with repetitive stimulation cycles was not affected in the presence of neutralizing anti-IL-4 antibodies. These results indicate that CD28 activation may play an important role in the differentiation of the Th2 subset in humans.