Deficient lymphokine production of newborn lymphocytes

Preterm infants have deficient monocyte and lymphocyte cytokine responses to group B streptococcus

Group B streptococcus (GBS) is an important cause of early- and late-onset sepsis in the newborn. Preterm infants have markedly increased susceptibility and worse outcomes, but their immunological responses to GBS are poorly defined. We compared mononuclear cell and whole-blood cytokine responses to heat-killed GBS (HKGBS) of preterm infants (gestational age [GA], 26 to 33 weeks), term infants, and healthy adults. We investigated the kinetics and cell source of induced cytokines and quantified HKGBS phagocytosis. HKGBS-induced tumor necrosis factor (TNF) and interleukin 6 (IL-6) secretion was significantly impaired in preterm infants compared to that in term infants and adults. These cytokines were predominantly monocytic in origin, and production was intrinsically linked to HKGBS phagocytosis. Very preterm infants (GA, <30 weeks) had fewer cytokine-producing monocytes, but nonopsonic phagocytosis ability was comparable to that for term infants and adults. Exogenous complement supplementation increased phagocytosis in all groups, as well as the proportion of preterm monocytes producing IL-6, but for very preterm infants, responses were still deficient. Similar defective preterm monocyte responses were observed in fresh whole cord blood stimulated with live GBS. Lymphocyte-associated cytokines were significantly deficient for both preterm and term infants compared to levels for adults. These findings indicate that a subset of preterm monocytes do not respond to GBS, a defect compounded by generalized weaker lymphocyte responses in newborns. Together these deficient responses may increase the susceptibility of preterm infants to GBS infection.

Glyceraldehyde-3-phosphate dehydrogenase is a reliable internal control in Western blot analysis of leukocyte subpopulations from children

To study differences in the development of immunity, leukocytes from cord blood are often compared with those from adult peripheral blood. Western blot analysis is a common method for detecting proteins. In this study, we investigated the reliability of using different housekeeping proteins (β-actin, β-tubulin, and glyceraldehyde-3-phosphate dehydrogenase [GAPDH]) as internal controls for different leukocyte subpopulations from infants, children, and adults. Our results showed that the expression levels of β-actin and β-tubulin were much lower in cord blood leukocytes than in adult leukocytes, and this expression pattern persisted in children up to 3 years old. Further study revealed that the β-actin expression level in newborns was especially lower in CD14-positive monocytes. However, cord blood and adult peripheral blood monocytes had similar expression levels of β-actin messenger RNA (mRNA). Further experiments showed that posttranslational regulation was responsible for the low β-actin expression level in neonatal monocytes. Thus, researchers should carefully assess the appropriate use of housekeeping gene-encoded proteins as internal standards to normalize samples for comparisons of different leukocyte populations from subjects of different ages. In this study, we determined that GAPDH was a more reliable internal control than others in Western blot analysis for comparing the development of immunity among infants, children, and adults.

The antimicrobial function of milk lipids

Milk lipids serve not only as nutrients but as antimicrobial agents that constitute a defense system against microbial infections that occur at mucosal surfaces. The lipid fraction of milk develops antimicrobial activity in the gastrointestinal tract of suckling neonates as a result of lipolytic activity which converts milk triglycerides to antimicrobial fatty acids and monoglycerides. Antimicrobial milk lipids may be particularly important in protecting infants with an inadequate secretory immune response from infection. The lipid-dependent antimicrobial activity of milk is due to medium-chain saturated and long-chain unsaturated fatty acids and their respective monoglycerides released by lipases in the gastrointestinal tract. The antimicrobial activity of fatty acids and monoglycerides is additive and consequently it is their combined concentration that determines the lipid-dependent antimicrobial activity of milk. Microbial inactivation occurs rapidly by membrane destabilization. The antimicrobial activity of milk lipids can be duplicated using purified fatty acids and monoglycerides. It should be possible, therefore, to supplement banked human milk to provide lipid-dependent antimicrobial activity from the moment of ingestion (Schanler et al., 1986). This could reduce the risk of viral transmission from mother to infant through milk. Milk lipids also could be adapted for use at mucosal surfaces other than those in the gastrointestinal tract to reduce vertical transmission of pathogens during birth.

Functional analyses of cord blood natural killer cells and T cells: a distinctive interleukin-18 response

OBJECTIVE

To search for the functional property of cord blood (CB) cells, the effects of interleukin-18 (IL-18) on interferon-gamma (IFN-gamma) production of T cells or natural killer (NK) cells were compared between CB and adult peripheral blood (PB).

MATERIALS AND METHODS

T cells, CD45RA(+) T cells, and NK cells were purified from CB and adult PB mononuclear cells using magnetic beads or a cell sorter. After stimulation with or without IL-18 in the presence of IL-12 for 48 hours (NK cells) or 72 hours (T cells or CD45RA(+) T cells), IFN-gamma concentration was measured in each subset. Although IL-18 induced significant IFN-gamma production from both CB and adult PB T cells in the presence of IL-12, the IFN-gamma levels from CB T cells were lower than those from adult PB T cells. However, CD45RA(+) T cells from CB and from adult PB produced similar levels of IFN-gamma after stimulation with IL-18 + IL-12. On the other hand, CB NK cells exhibited higher IFN-gamma production and CD69 expression than adult PB NK cells after stimulation with IL-18 + IL-12. Cytolytic activity of CB NK cells increased to a level comparable to that of adult PB NK cells after the same IL-18/IL-12 stimulation.

CONCLUSIONS

These results suggest that a low response of CB T cells to IL-18 is due to a higher proportion of naive (CD45RA(+)) T cells in CB, which may be one of the factors responsible for the neonatal immaturity of the immune system as well as the low incidence of graft-vs-host disease in patients receiving CB stem cell transplantation. On the other hand, a high response of CB NK cells to IL-18 may contribute to the host defense during the neonatal period and antitumor effects in CB stem cell transplantation.

[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.

Relative immunocompetence of the newborn harbour seal, Phoca vitulina

The immune system of many mammalian species is not fully developed at birth, with newborns obtaining temporary immunological protection from maternal antibodies. Little is known of the immune system of the harbour seal, and developmental aspects of its immune system have not been systematically studied. We collected blood and milk samples from nine free-ranging mother-pup pairs throughout the lactation period on Sable Island, Canada, in an effort to characterise developmental aspects of the immune system of this newborn pinniped. Pup lymphocytes responded stronger to the mitogens concanavalin A, phytohaemagglutinin, and pokeweed mitogen than the lymphocytes of their mothers. In contrast to newborn cats and dogs, newborn seal pups developed high specific antibody responses after immunisation with an inactivated rabies vaccine. Circulating levels of total IgG in newborn pups were low (3% of maternal levels), but increased rapidly after colostrum intake (to 65% of maternal levels after 15 days). A similar pattern of increase in pup serum was observed for phocine distemper virus specific antibodies which had been detected in the serum and milk of mothers, suggesting that the transfer of colostral antibodies is an important feature of temporary protection for the pup. We speculate that the relative immunocompetence of the harbour seal at birth reflects an adaptation to its relatively short nursing period and limited maternal care.

Cytokine response of neonates to surgery

Cytokines are early responders in the cascade of host mediators after injury. The cytokine response in neonates following surgery and its prognostic significance were studied prospectively. Twenty-one patients (oesophageal atresia [5], congenital diaphragmatic hernia [4], exomphalos [4], patent vitellointestinal duct [1], anorectal anomaly [2], choledochal cyst [1], renal cyst [1], ovarian cyst [1], myelomeningocoele [1], and pyloric stenosis [1]) operated on at a median age of 3 days (range, 1 to 24 days) and 12 age-matched controls were included in the study. Plasma samples were obtained once in the controls, and serially preoperatively and at 1, 3, 6, 12, 24, 36, and 48 hours postoperatively in the patients. The levels of the cytokines, interleukin-6 (IL-6), and interleukin-8 (IL-8) were measured using the enzyme-linked immunosorbent assay (ELISA) technique. The median plasma levels of IL-6 and IL-8 in normal controls were 2.4 pg/mL and 92.0 pg/mL, respectively. Of the 21 patients, four had postoperative complications (pulmonary consolidation [2], septicaemia [1], and oesophageal leak [1]) between days 4 and 6. All 17 uncomplicated cases had an increase in IL-6 and IL-8 in the early postoperative period, with the peak occurring within 12 hours after surgery. The mean (+/- SEM) peak levels of IL-6 and IL-8 in uncomplicated cases were of 92.6 +/- 15.8 pg/mL and 230.3 +/- 45.3 pg/mL, respectively. In the four complicated cases, there was a disproportionately higher increase in both IL-6 (peaks, 305.0, 125.0, 240.0, and 220.0 pg/mL) and IL-8 (peaks, 1500.0, 340.0, 245.0, 355.0 and pg/mL), which preceded the clinical onset of complications. The early postoperative increases in plasma IL-6 and IL-8 probably represent the stress response of neonates to surgery. Furthermore, the association of an exaggerated increase in postoperative levels of plasma IL-6 and IL-8 and postoperative complications may have prognostic significance.

Cord blood contains cells secreting antibodies to nervous system components

Umbilical cord blood of newborns and peripheral blood of healthy adults were investigated by an immunospot assay for cells secreting IgG, IgA and IgM antibodies against myelin basic protein (MBP), proteolipid protein (PLP), myelin-associated glycoprotein (MAG) and myelin oligodendrocyte glycoprotein (MOG) which represent putative antigens for an autoimmune attack in multiple sclerosis (MS) and against acetylcholine receptor (AChR) which is considered an important autoantigen in myasthenia gravis. Cells secreting antibodies against one or more of these autoantigens were detected in 18 out of 24 newborns, and in eight out of 20 adults. Eight of the cord blood samples contained cells secreting antibodies of IgG, IgA and/or IgM isotypes to one antigen, five to two antigens, two to three antigens, two to four antigens, and one to five antigens. Most prominent were anti-MBP IgG antibody secreting cells which were detected in 13 newborns at a mean number of 1/20,000 cord blood cells, and in six adults at a mean number of 1/10(5) peripheral blood cells. Anti-AChR IgG antibody secreting cells were detected in four out of 12 newborns versus four out of 14 peripheral blood specimens, at mean values of 1/10(5) cells in both instances. Cells secreting autoantibodies of IgA and IgM isotypes were less frequent both in cord blood and peripheral blood. The occurrence of nervous tissue autoantibody secreting cells in newborns must be related to a possible primary role of such autoantibodies in MS and myasthenia gravis.

Lymphokine-activated killer cells in primary immunodeficiencies and acquired immunodeficiency syndrome

Cytotoxic mechanisms (e.g., natural killer (NK) lysis, antibody-dependent cellular cytotoxicity, and cytotoxic T lymphocyte lysis) play an important role in host defense against various infections and neoplasms. Lymphokine-activated killer (LAK) cytotoxicity, induced in vitro by incubating mononuclear cells with interleukin 2 (IL-2) for 2-5 days, may also represent an important component of the body's cytotoxic repertoire. In 10 patients with congenital cellular immunodeficiencies, including 5 with severe combined immunodeficiency, the mean LAK activity in a 3-hr chromium release assay against Raji target cells was 44 +/- 8.1%, which is equivalent to that observed in normal adults and neonates. In only one case, a patient with reticular dysgenesis, was there absent LAK cell generation. Haploidentical T cell-depleted bone marrow transplantation (BMT) restored LAK activity in this patient. LAK activity was first observed in this patient and two others 3-6 weeks following BMT, prior to other evidence of immunologic engraftment such as lymphocyte proliferation to mitogens, NK activity, or interferon-gamma production. One patient with adenosine deaminase deficiency showed normal levels of LAK activity despite absent NK activity. Three patients with chronic granulomatous disease also had normal LAK activity (57 +/- 14% specific lysis). In 9 patients with acquired immunodeficiency syndrome (AIDS), IL-2 activation resulted in a mean cytotoxic activity of 56 +/- 8.7% toward Raji targets. In addition, 9 patients with pre-AIDS complex also showed normal levels of cytotoxicity (37 +/- 3.3% toward Raji targets), equivalent to that of 8 normal controls, including two healthy homosexual males (mean lysis 38 +/- 3.9%). These results indicate that LAK cells appear early in immunologic ontogeny. Further, the mechanism of lysis is not oxygen dependent since LAK activity was present in the 3 patients with chronic granulomatous disease. The ability to generate LAK in a wide spectrum of immunodeficiencies may indicate that IL-2 could be used in therapy of such disorders.

Pulmonary surfactant inhibits priming of rabbit alveolar macrophage. Evidence that surfactant suppresses the oxidative burst of alveolar macrophage in infant rabbits

We have investigated the possible role of pulmonary surfactant in mediating a deficiency in alveolar macrophages (AM) from infant animals to produce chemiluminescent (CL) responses elicited by phorbol myristate acetate (PMA) or opsonized zymosan (Op-Zym). Freshly harvested AM from rabbits 7 to 28 days of age produced much reduced PMA-elicited CL responses compared to 5- to 6-month-old rabbits. Initially we observed that AM from both infant and adult rabbits exhibited increasing PMA- or Op-Zym-elicited CL responses in a time-dependent manner when they were incubated in RPMI 1640 medium without serum for more than 3 h. In addition, AM from infant rabbits acquired the capacity to become primed with macrophage activation factor (MAF) containing supernatants or fetal bovine serum (FBS) during an 18-h incubation period that was basically equivalent to that of AM from adult rabbits. Our studies reveal that natural and artificial surfactant inhibited "spontaneous" priming as well as priming of AM induced by MAF-containing supernatant or FBS for producing PMA- or OP-Zym-elicited CL responses from both normal infant and adult animals. In addition, these surfactant preparations also suppressed the response of AM from adult BCG-sensitized rabbits during the course of an 18-h incubation period. It is especially noteworthy that AM from infant rabbits appeared to be more susceptible to the inhibitory activity of surfactant than AM from adult animals. Our data indicate that freshly harvested AM from infant rabbits are under greater suppression than AM from adult rabbits in terms of their capacities to produce oxidative responses.(ABSTRACT TRUNCATED AT 250 WORDS)