Function and cell biology of neutrophils and mononuclear phagocytes in the newborn infant

The inflammatory response to injury in children

PURPOSE OF REVIEW

Severely injured children have a decreased incidence and different pattern of multiple organ failure when compared with adults. This article reviews recent advances in understanding the mechanisms leading to this discrepancy.

RECENT FINDINGS

Post injury, inflammation-related outcomes are age-related, as demonstrated by epidemiological and laboratory investigations that confirm a relative protection from acute lung injury and multiple organ failure in children. The importance of the innate immune system in initiating and regulating the inflammatory response to injury is also increasingly well understood, but relatively little research has focused on the implications of a maturing innate immune system for the inflammatory response to injury in children. The development of age-appropriate immunomodulatory interventions for the prevention and treatment of postinjury inflammatory dysregulation depends on continued investigation of mechanisms responsible for the unique pediatric inflammatory response to trauma.

SUMMARY

The inflammatory response to injury in children is functionally and mechanistically unique, as suggested by age-related differences in the incidence and pattern of systemic inflammation and multiple organ failure after major trauma. We review the current clinical and basic science literature related to postinjury inflammation in childhood, focusing on the developmental biology of innate immunity and the implications of a maturing immune system for trauma-related interventions and outcomes.

Differential gene expression signatures of adult peripheral blood vs cord blood monocyte-derived immature and mature dendritic cells

OBJECTIVE

Our previous studies have demonstrated differentially expressed genetic signature patterns in adult peripheral blood (APB) monocytes (Mos) vs cord blood (CB) Mos.

MATERIALS AND METHODS

In this study, we examined the differential gene expression profiles of APB vs CB immature dendritic cells (iDCs) and mature dendritic cells (mDCs) derived from Mos.

RESULTS

By utilizing oligonucleotide microarray, significant differential gene expression signature patterns were identified in APB vs CB mDCs, including increased expression of chemokines, cytokine receptors, and cell surface molecules. Additionally, signaling protein genes were significantly overexpressed in APB vs CB mDCs. There was also a significant amplification of expression of transcription factor interferon (IFN) regulatory factors and structure regulatory genes in APB vs CB mDCs. In contrast, there were genes expressed significantly higher in CB vs APB mDCs, including cell-cycle regulators and signaling molecule gene.

CONCLUSION

Taken together, these results suggest that specific genetic signatures might be responsible for differential DC differentiation and maturation between APB vs CB, and may provide insight into molecular mechanisms regulating differential immune responses between neonates and adults.

Deficient TACI expression on B lymphocytes of newborn mice leads to defective Ig secretion in response to BAFF or APRIL

Capsular polysaccharides of encapsulated bacteria do not induce immune response in newborns and the mechanism for this unresponsiveness is not clear. In adults, transmembrane activator and calcium-modulator and cyclophilin [corrected] ligand interactor (TACI) is a TNFR family member molecule with a pivotal role in Ab responses against polysaccharide vaccines. We investigated the expression and the functions of the TNF family cytokines, B cell-activating factor of the TNF family (BAFF) and a proliferation-inducing ligand (APRIL), and their receptors in newborn mice and found that TACI expression on B lymphocytes was dramatically reduced (p < 0.0001) in newborns as compared with adults. More importantly, TACI ligands BAFF or APRIL were unable to induce IgA/IgG/IgM secretion from newborn B lymphocytes. Additionally, TACI expression seems to be important in plasma cell development. Indeed, in contrast to adults, stimulation of newborn B lymphocytes with BAFF or APRIL did not result in up-regulation of CD138 expression. In vitro or in vivo exposure of newborn B lymphocytes to oligodeoxynucleotides (CpG ODN) led to up-regulation of TACI expression on newly formed, follicular, and marginal zone as well as B1 B lymphocyte populations, and rendered them responsive to BAFF- or APRIL-mediated CD138 expression and IgA/IgG secretion. Finally, immunization of newborn BALB/c mice but not TACI knockout mice with CpG ODN containing (4-hydroxy-3-nitrophenyl)acetyl-Ficoll led to development of IgG Abs against (4-hydroxy-3-nitrophenyl)acetyl. These findings demonstrate that low TACI expression may be a critical factor that determines the susceptibility of newborns to infections with encapsulated bacteria and the impaired immunogenicity of polysaccharide vaccines. Finally, CpG ODNs may correct deficient newborn response to polysaccharide vaccines by up-regulating TACI.

Gamma interferon production in response to Mycobacterium bovis BCG and Mycobacterium tuberculosis antigens in infants born to human immunodeficiency virus-infected mothers

In utero sensitization to infectious pathogens can establish immunological memory and may influence the immune response to unrelated antigens. Little is known about the influence of intrauterine human immunodeficiency virus (HIV) exposure on the cellular immune response to mycobacterial antigens. Whole-blood culture gamma interferon (IFN-gamma) production in response to mycobacterial antigens was measured at birth and 6 weeks of age to determine the characteristics of the IFN-gamma response in HIV-exposed infants to Mycobacterium bovis BCG and mycobacterial antigens. At birth, we observed an increased immune activation in response to phytohemagglutinin among HIV-exposed, uninfected infants. In a proportion of these infants, we also observed an increased immune activation in response to purified protein derivative, BCG, and early secreted antigen target 6. Increases in the IFN-gamma response to the four antigens between birth and 6 weeks of age, observed in all HIV-unexposed infants, was absent in a substantial proportion of HIV-exposed, uninfected infants. The immunological differences persisted at 6 weeks of age, suggesting a sustained impact of in utero immune priming by HIV. Intrauterine exposure to HIV affects the infants' cellular immune response to mycobacterial antigens, either specifically or as a consequence of nonspecific, broadly reactive immune activation. Further studies will be important to help determine optimal vaccination and disease prevention strategies for this vulnerable population group.

Immune control of Babesia bovis infection

Babesia bovis causes an acute and often fatal infection in adult cattle, which if resolved, leads to a state of persistent infection in otherwise clinically healthy cattle. Persistently infected cattle are generally resistant to reinfection with related parasite strains, and this resistance in the face of infection is termed concomitant immunity. Young animals are generally more resistant than adults to B. bovis infection, which is dependent on the spleen. Despite the discovery of B. bovis over a century ago, there are still no safe and effective vaccines that protect cattle against this most virulent of babesial pathogens. Immunodominant antigens identified by serological reactivity and dominant T-cell antigens have failed to protect cattle against challenge. This review describes the innate and acquired immune mechanisms that define resistance in young calves and correlate with the development of concomitant immunity in older cattle following recovery from clinical disease. The first sections will discuss the innate immune responses by peripheral blood- and spleen-derived macrophages in cattle induced by B. bovis merozoites and their products that limit parasite replication, and comparison of natural killer cell responses in the spleens of young (resistant) and adult (susceptible) cattle. Later sections will describe a proteomic approach to discover novel antigens, especially those recognized by immune CD4+ T lymphocytes. Because immunodominant antigens have failed to stimulate protective immunity, identification of subdominant antigens may prove to be important for effective vaccines. Identification of CD4+ T-cell immunogenic proteins and their epitopes, together with the MHC class II restricting elements, now makes possible the development of MHC class II tetramers and application of this technology to both quantify antigen-specific lymphocytes during infection and discover novel antigenic epitopes. Finally, with the imminent completion of the B. bovis genome-sequencing project, strategies using combined genomic and proteomic approaches to identify novel vaccine candidates will be reviewed. The availability of an annotated B. bovis genome will, for the first time, enable identification of non-immunodominant proteins that may stimulate protective immunity.

Novel microtechnique for assessment of postnatal maturation of the phagocytic function of neutrophils and monocytes

We describe a simple test for the evaluation of phagocytosis and provide a chart of reference values to evaluate normal phagocytosis by age. We assessed the postnatal maturation of phagocytic function of neutrophils and monocytes. Phagocytosis was evaluated in newborn children delivered vaginally or by cesarean section, infants, preschool children, schoolchildren, and adult subjects. Two drops of blood were placed on a microscope slide and incubated with Saccharomyces cerevisiae yeasts, and phagocytosis was evaluated by microscopy. Our technique showed results comparable to or better than those obtained by other usual techniques. The neutrophils of newborn children delivered by cesarean section showed a phagocytic capacity 45% higher than those of neonates delivered vaginally, whereas neutrophils from children in the latter group showed the lowest phagocytic capacity of all age groups. Phagocytosis by neutrophils reached the levels seen in adults at about the first year of life, while there were no important variations in phagocytosis by monocytes in the different age groups. The technique described is reliable and fast, uses only a few drops of blood, and allows better preservation of cell function due to the minimal manipulation to which the cells are submitted. The delayed maturation of the phagocytic function by neutrophils may account for the high levels of susceptibility of newborn and infant children to bacterial infections. This practical method of assessment of phagocytosis may allow the diagnosis of primary or secondary phagocytic deficiencies to be made more easily and may allow better monitoring and treatment of those with dysfunctions of these cells.

Differential gene expression patterns by oligonucleotide microarray of basal versus lipopolysaccharide-activated monocytes from cord blood versus adult peripheral blood

Monocytes (Mo) are critically important in the generation of inflammatory mediators, cytokines/chemokines, and regulation of innate and adaptive immune responses. We and others have previously demonstrated significant dysregulated cytokine gene expression and protein production and in vitro functional activities of activated cord blood (CB) vs adult peripheral blood (APB) mononuclear cells (MNC). In this study, we compared, by oligonucleotide microarray, the differential gene expression profiles of basal and LPS-activated APB vs CB Mo. We demonstrated a significant increase in the gene expression of several important functional groups of CB genes compared with basal levels including cytokine (IL-12p40, 5-fold), immunoregulatory (signaling lymphocytic activation molecule, 4-fold), signal transduction (Pim-2, 3-fold), and cell structure (Rho7, 4-fold) among others. Furthermore, there was significantly differentially amplified gene expression in LPS-activated APB vs LPS-activated CB Mo, including cytokine (G-CSF, 14-fold), chemokine (macrophage-inflammatory protein 1alpha, 5-fold), immunoregulatory (MHC DRB1, 5-fold), transcription factor (JunB, 4-fold), signal transduction (STAT4, 5-fold), apoptotic regulation (BAX, 5-fold), and cell structure (ladinin 1, 6-fold) among others. These results provide insight into the molecular basis for normal genetic regulation of Mo development and cellular function and differential inflammatory and innate and adaptive immune responses between activated CB and APB Mo.

Phenotypic and functional comparison of monocytes from cord blood and granulocyte colony-stimulating factor-mobilized apheresis products

OBJECTIVE

It is well established that T cells are effector cells in graft-vs-host disease (GVHD), yet the contribution of graft monocytes is less well characterized. Therefore, monocytes in cord blood (CB) and granulocyte colony-stimulating factor-mobilized apheresis products (G-AP), two stem cell grafts associated with reduction of acute and chronic GVHD and relative reduction of acute GVHD, respectively, were compared phenotypically and functionally.

MATERIALS AND METHODS

The frequencies, phenotypes, and pinocytosis activities of monocytes from CB and G-AP were determined by flow cytometry and their allostimulatory potential in a primary mixed leukocyte reaction.

RESULTS

G-AP contained significantly more monocytes than CB (24.9% +/- 7.1% vs 8.8% +/- 1.5% CD14+ and 62.4 +/- 27.5 x 10(6) vs 0.9 +/- 0.2 x 10(6) CD14+ cells/mL). Monocytes from both sources revealed similar phenotypes. They expressed CD4, CD11a, CD11b, CD11c, CD18, CD32, CD33, CD45R0, CD48, CD50, CD54, CD58, CD64, CD86, CD102, CD116, CD123, and HLA-DR; showed no expression of CD1a and CD83; and weak expression of CD16, CD45RA, and CD80. The levels of CD80 and CD86 expression were comparable; however, in contrast to G-AP monocytes, CB monocytes lacked CD40. There was no difference in pinocytosis activity and allostimulatory capacity of CB and G-AP monocytes.

CONCLUSIONS

Monocytes in CB and G-AP are phenotypically and functionally comparable. The only difference observed is the lack of CD40 on CB monocytes.

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.

Th1 T-cell and monocyte defects

Mutations predisposing to infections with intracellular pathogens and affecting Th1 T-cells and monocytes have been identified in the past few years. In this article, the authors review the interaction of T cells and monocytes in the context of host defense against intracellular pathogens. Known genetic defects in these pathways are summarized.

Cellular immune responses in neonates

Reduced numbers of lymphocytes and antigen presenting cells have been described as some of the main factors responsible for antigenic tolerance or low responsiveness in neonates. However, by changing the parameters of immunization, such as dose of antigen and frequency of antigen presenting cells we and others have shown that neonates have the option of developing the same variety of immune responses seen in adults. Several aspects of the development of cellular immunity in human and murine neonates are reviewed in this article, with a special focus on the development of T cell mediated responses, from ontogeny to effector function.

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

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