Nitric oxide, prostaglandins, and impaired cerebral blood flow autoregulation in group B streptococcal neonatal meningitis.

Impaired autoregulation of cerebral blood flow (CBF) contributes to CNS damage during neonatal meningitis. We tested (i) the hypothesis that cerebrovascular autoregulation is impaired during early onset group B streptococcal (GBS) meningitis, (ii) whether this impairment is regulated by vasoactive mediators such as prostaglandins and (or) nitric oxide (NO), and (iii) whether this impairment is preventable by specific and (or) nonspecific inhibitors: dexamethasone, ibuprofen, and Nomega-nitro-L-arginine, a NO inhibitor. Sterile saline or 10(9) colony-forming units (cfu) of heat-killed GBS was injected into the cerebral ventricle of newborn piglets. CBF autoregulation was determined by altering cerebral perfusion pressure (CPP) with balloon-tipped catheters placed in the aorta. GBS produced a narrow range of CBF autoregulation due to an impairment at the upper limit of CPP. We report that in vivo in the early stages (first 2 h) of induced GBS inflammation (i) GBS impairs the upper limit of cerebrovascular autoregulation; (ii) ibuprofen, dexamethasone, and Nomega-nitro-L-arginine not only prevent this GBS-induced autoregulatory impairment but improve the range of cerebrovascular autoregulation; (iii) these autoregulatory changes do not involve circulating cerebral prostanoids; and (iv) the observed changes correlate with the induction of NO synthase gene expression. Thus, acute early onset GBS-induced impairment of the upper limit of CBF autoregulation can be correlated with increases of NO synthase production, suggesting that NO is a vasoactive mediator of CBF.

Deregulation of cyclooxygenase and nitric oxide synthase gene expression in the inflammatory cascade triggered by experimental group B streptococcal meningitis in the newborn brain and cerebral microvessels.

Group B Streptococcus (GBS) is the most common cause of neonatal sepsis and meningitis. Despite antibiotics, GBS in the newborn initiates a cascade of molecular and biological events leading to altered cerebral perfusion, blood-brain barrier disruption, cerebral edema, intracranial hypertension, neurological damage, and even death. Having previously shown that GBS infection impairs cerebral blood flow autoregulation and increases prostaglandin (PG) levels, we examined the regulation of some crucial inflammatory mediators (PGs, nitric oxide (NO), tumor necrosis factor-a) in the brain and cerebral microvessels (MVs) from newborn piglets. Cyclooxygenase (COX), the key enzyme in PG biosynthesis, exists in two isoforms, COX-1 and COX-2. Both may be directly induced by NO in a model of renal inflammation. Besides its neurotransmitter role, NO is a potent vasorelaxant whose production is catalyzed by at least three distinct nitric oxide synthases (NOS) (bNOS, ecNOS, iNOS). Western blot analyses showed that the newborn (4 day old) brain expressed lower levels of COX-1 (8-fold), COX-2 (20-fold), bNOS (12-fold), and ecNOS (5-fold) than in the 1 day old. MV showed approximately equal levels of COX-2, lower levels of COX-1 (4-fold), bNOS (5-fold), and higher levels of ecNOS (20-fold) in comparison to 4-day-old cerebral MV. A 4-day-old brain expressed lower levels of bNOS (5-fold), ecNOS (10-fold), and COX-1 (2-fold) than the 6-week-old pig. COX-2 protein was undetected in a 4-day-old pig brain, but present in great excess in MV. Purified MV showed lower ecNOS (14-fold), COX-1 (2-fold), and about equal levels of bNOS and COX-2 in comparison with MV from 6-week-old pigs. Reverse transcription polymerase chain reaction analyses confirmed these results. Treatment with noo-nitro-L-arginine (LNA), a NOS inhibitor, downregulated COX-1 expression in the newborn brain and both COX-1 and COX-2 cerebral MV expression. GBS infection (10(9) colony-forming units, 0.5 mL intracerebroventricular) of sedated newborn piglets induced the expression of tumor necrosis factor-alpha in the cerebrospinal fluid after 2 hours, upregulated bNOS expression in both brain and MVs, upregulated ecNOS in MVs, and downregulated COX-1, COX-2, and ecNOS in the brain. GBS did not trigger the expression of iNOS. Our data suggest that there is a net deficiency of NOS isoforms in the immature brain and microvasculature of the 4-day-old piglet and that the differences in expression lead to the immature control of NO and PG production, rendering newborns particularly susceptible to neurological damage because of the undeveloped nature of their response mechanisms. Moreover, the GBS-induced cascade deregulates the gene expression of interacting inflammatory mediators and may cause a net vasoconstrictor/vasodilator imbalance, leading to cerebral hypertension and edema in the early stages of infection. Pharmacological manipulations of the inflammatory cascade could lead to novel therapeutic approaches for the treatment of GBS meningitis.

Biochemical mediators of meningeal inflammatory response to group B streptococcus in the newborn piglet model.

The meningeal inflammatory response to a heat-killed mutant unencapsulated strain of type III group B Streptococcus (GBS) was studied in a newborn piglet model. GBS (10(9) colony-forming unit equivalents) or saline (control) was inoculated intraventricularly. Serial cerebrospinal fluid measurements were done at baseline and over the course of the next 24 h for cytochemical changes and production of tumor necrosis factor (TNF) and prostaglandins. In separate experiments, we defined the time course of early changes during the first 6 h and dose response relationship over a range of inocula 10(6) to 10(9) colony-forming unit equivalents. The intraventricular inoculation of the heat-killed unencapsulated GBS induced marked leukocytosis and increased protein by 6 h. These changes were preceded by a several hundredfold increase in TNF (maximum at 2 h) and prostaglandins (maximum at 2-4 h). The early and sharp rise in TNF suggests its pivotal role in initiating the inflammatory cascade. The magnitude of the inflammatory response increased with increasing bacterial dose over the range studied. To study the effect of encapsulation of GBS in the induction of meningeal inflammation, we compared the response to the unencapsulated mutant strain with that to the encapsulated parent strain. The encapsulated strain produced much smaller inflammatory changes, and only with high doses of bacteria. The GBS cell wall appeared to be the primary bacterial product triggering inflammation. Intraventricular injection of the heat-killed unencapsulated GBS with exposed cell wall can serve as a valid model for studying neonatal meningitis.

Neutrophil Fc receptor participation in phagocytosis of type III group B streptococci.

Human peripheral blood neutrophils bear receptors for immunoglobulin G, FcRII, and FcRIII that differ structurally and functionally. We investigated the role of FcRII and FcRIII in the phagocytosis of group B streptococci (GBS) by measuring neutrophil uptake of radiolabeled type III GBS. The mean uptake of GBS opsonized with human serum containing complement and specific antibody was 76%, but when this serum was heated, the mean uptake was only 22%. A monoclonal antibody to FcRIII, Leu-11b, inhibited in a dose-dependent manner uptake of GBS opsonized with heated or intact serum to maxima of 40 and 30%, respectively. Conversely, a monoclonal antibody to FcRII, IV.3, inhibited by 77% the uptake of GBS opsonized with heated serum but had no effect when GBS was opsonized with intact serum. Leu-11b and IV.3 had an additive inhibitory effect with heated but not with intact serum. Neither monoclonal antibody inhibited the uptake of GBS opsonized with hypogammaglobulinemic serum. Therefore, FcRII is the primary mediator of the phagocytosis of GBS opsonized by antibody alone, whereas FcRIII plays a lesser role. Surprisingly, FcRII is not necessary for phagocytosis when complement is also present. FcRIII participates, to a limited extent, in phagocytosis of GBS opsonized with antibody whether or not complement is present. These findings suggest that the function of FcRII in triggering phagocytosis may be particularly important in host defense against type III GBS in the setting of complement deficiency of young infants.

Prevention of group B streptococcal infection.

Group B streptococci continue to be major perinatal pathogens, both for mothers and their infants, and are associated with significant morbidity, mortality, and its attendant cost to society. Approaches to prevention are directed toward either eliminating exposure to the organism or enhancing host resistance, that is, chemoprophylaxis and immunoprophylaxis. Intrapartum chemoprophylaxis has been shown to effectively interrupt vertical transmission of group B streptococci from the genitally colonized mother to the infant and to decrease the incidence of both maternal and early-onset neonatal group B streptococcal disease. To avoid unnecessarily exposing large numbers of colonized women to antibiotics, only those with defined risk factors should be selected for intrapartum chemoprophylaxis. This regimen is ampicillin given intravenously, 2 g initially at onset of labor or rupture of membranes, followed by 1 g every 4 hours until delivery. Risk factors include premature onset of labor or rupture of membranes before 37 weeks' gestation, rupture of membranes of more than 12 hours, intrapartum fever, group B streptococcal bacteriuria, or having previously delivered an infant with group B streptococcal disease. Detection of anogenital colonization is accomplished either by culture late in the second or early in the third trimester or by intrapartum group B streptococcal antigen testing of vaginal swabs from those previously culture-negative or not cultured. Although this approach combines the advantages of several proposed strategies, it will still miss those cases of group B streptococcal disease developing in the absence of discernible risk factors. Intrapartum prophylaxis does not prevent late-onset group B streptococcal disease. Prenatal and postnatal chemoprophylaxis have not been shown to be effective. Symptomatic infants born to mothers given chemoprophylaxis should be evaluated for neonatal sepsis and treated accordingly. This approach is also suggested for asymptomatic premature infants, those whose mothers have not received adequate prophylaxis or have previously delivered infants with group B streptococcal disease, and for twin siblings of infants developing group B streptococcal disease. Successful implementation of this approach may be limited by the availability and sensitivity of the rapid antigen test used. Immunoprophylaxis, and active immunization in particular, is the most promising method of preventing perinatal group B streptococcal disease in mothers and their infants, including late-onset disease. Immunization of pregnant women with type III polysaccharide vaccine has resulted in adequate provision of functional antibody to the infants born to responders.(ABSTRACT TRUNCATED AT 400 WORDS)

Potential use of intravenous immune globulin for group B streptococcal infection.

Several lines of evidence suggest that passive immunization as adjunctive therapy for or prevention of group B streptococcal (GBS) sepsis in neonates will require the use of preparations of human intravenous immune globulin (IVIG) that are hyperimmune for protective antibodies to GBS. Results from both in vitro and in vivo experiments utilizing commercially available IVIG preparations suggest that the doses necessary for achieving levels of pathogen-specific antibody capable of promoting efficient opsonization and phagocytosis of GBS may be prohibitive. Several laboratories have reported that standard IVIG preparations contain only modest levels of antibodies to the four capsular polysaccharides of GBS (the protective moieties), are variable in their effect on in vitro opsonophagocytosis by dose and method of preparation, and are significantly less protective in animal models than is IVIG prepared from adults immunized with GBS polysaccharide vaccines. Further, when we gave a single infusion of standard IVIG at a dose of either 500 or 750 mg/kg to 10 premature neonates during the first week of life, opsonophagocytosis of type III GBS by their sera and adult neutrophils was observed only when high levels of specific antibody were achieved, levels only transiently achieved in nonimmune infants. Commercial preparation of human immune globulin hyperimmune for GBS will be required for optimal adjunctive therapy in patients with sepsis due to GBS and for the possible prevention of late-onset infant disease.

Role of intravenous immunoglobulin in prevention of late-onset infection in low-birth-weight neonates. The Neonatal IVIG Study Group.

As a result of inadequate placental transport of maternal IgG, preterm neonates of less than 32 weeks' gestation, especially those with birth weights less than 1,500 g, are profoundly hypogammaglobulinemic at birth, a condition that worsens during the first several weeks of life. This hypogammaglobulinemia is believed to contribute to their high frequency of late-onset sepsis, with its accompanying morbidity and mortality. Animal studies suggest that human immunoglobulin prepared for intravenous use (IVIG) improves host defense against pathogens that cause neonatal infections, but studies of IVIG in human neonates have been inconclusive because of the small numbers of infants included, lack of suitable controls, use of clinical rather than strict microbiologic definition of sepsis, and performance only in a single hospital outside the United States. A double-blind, randomized, placebo-controlled multicenter trial in the United States is in progress to determine the efficacy of IVIG in the prevention of late-onset infections in infants with birth weights between 500 and 1,750 g. Infants are infused with 500 mg of IVIG/kg or albumin-saline placebo at 3-7 days of age, 7 days later, and every 14 days for five doses. Efficacy parameters include mortality, number of proved infectious episodes (bacterial, fungal, or viral), and infection-related morbidity. Definitive guidelines for the possible use of prophylactic IVIG in low-birth-weight neonates should result from this evaluation of 500 to 700 infants in the United States.

Pharmacokinetics of intravenous immunoglobulin in very low birth weight neonates.

We studied the pharmacokinetics of single doses of intravenous immunoglobulin (IVIG) of 1000, 750 and 500 mg/kg administered to 21 neonates with birth weights from 750 to 1500 g. No adverse effects were detected. Mean pharmacokinetic values for the large, intermediate and small dose groups, respectively, were: elimination half-life, 19.6, 28.7 and 22.1 days; clearance, 5.2, 5.6 and 3.7 ml/kg/day; volume of distribution, 151, 255 and 130 ml/kg. Mean peak IgG concentrations in serum were 1826, 1476 and 1257 mg/dl for the large, intermediate and small dose groups, respectively. Mean IgG on post-infusion Days 1 to 28 were similar for the intermediate and small dose groups but were higher in the larger dose group. Both large and intermediate doses achieved larger increases in IgG over preinfusion values (delta IgG) than the small dose. The differences in delta IgG between the large and intermediate doses were less notable. The wide variability observed indicates that individualization of intravenous immunoglobulin dosage will be required in these patients.

Successful bone marrow transplantation with split lymphoid chimerism in DiGeorge syndrome.

A female infant with DiGeorge syndrome associated with severe T-cell immunodeficiency underwent a successful bone marrow transplantation from her HLA-identical, mixed leukocyte culture-nonreactive brother at 5 months of age. Mature circulating T cells and mitogen-induced proliferative responses were detectable at 10 days posttransplant, and by 8 months post-transplant functional T- and B-cell reconstitution was documented by normal responses to mitogens and normal levels of serum immunoglobulins as well as in vitro and in vivo T-cell reactivity to specific antigens and production of specific antibody to T cell-dependent antigens in vivo. Phytohemagglutinin-induced interleukin-2 production and cell surface interleukin-2 receptor expression improved posttransplant, with normal production values observed by 8 months posttransplant. Histologic examination of appendix and thoracic lymph node obtained 9 and 17 months posttransplant, respectively, revealed near-normal lymphoid architecture, with germinal center formation providing morphologic confirmation of reconstitution. Stable split lymphoid chimerism with T cells of donor origin and B cells remaining recipient in origin was documented by sex chromosome analysis. Two years posttransplant the subject remains free of serious infections. In conclusion, this case indicates that bone marrow transplantation can produce peripheral immunoreconstitution without need for significant thymic influence, most likely by providing a source of postthymic T cells, and that bone marrow transplantation should be considered a therapeutic option in patients with DiGeorge syndrome associated with severe T-cell deficiency.

Disposition of an immunoglobulin intravenous preparation in very low birth weight neonates.

To assess the disposition, tolerance, and toxicity of an intravenous preparation of immunoglobulin (IGIV) in very low birth weight (VLBW) neonates, we administered single doses of 500 or 750 mg/kg to 20 neonates with birth weights between 750 and 1500 g during the first week of life. The infusion of this product was well tolerated. Modest changes in hemoglobin, hematocrit, and total hemolytic complement occurred as expected. Hepatic toxic effects were not detected. Mean peak IgG concentrations were 1564 and 1316 mg/dL for the high-dose and low-dose groups, respectively. Mean IgG concentrations were very similar for both groups on postinfusion days 1, 4, 7, 14, 21, and 28. IgG concentrations remained above 300 mg/dL in seven of 10 infants in each group by day 21, and in six of the high-dose group and seven of the low-dose group by day 28. Mean elimination half-lives were 22.6 and 22.8 days in the high-dose and low-dose groups, respectively. These data provide a basis for assessment of potential efficacy of IGIV in the prevention of late-onset infection in VLBW neonates.

Unusual occurrence of an epidemic of type Ib/c group B streptococcal sepsis in a neonatal intensive care unit.

An epidemic of late-onset sepsis due to type Ib/c group B Streptococcus (Ib/c-GBS) occurred in a neonatal intensive care unit (NICU). During a seven-week period, five very low birth weight infants (index cases [ICs]) more than four weeks of age became bacteremic. Bacteriologic surveillance of neonates revealed persistent colonization in three ICs and identified three asymptomatic carriers (ACs). All ICs and one AC acquired Ib/c-GBS nosocomially, whereas the other two ACs were colonized at birth. Among nursery personnel, 39% carried GBS, but only two harbored Ib/c-GBS. Although phage typing of Ib/c-GBS isolates identified two patterns of susceptibility, we believe a single strain was involved in the epidemic, because the patterns overlapped and most isolates carried the same lysogenic phage. Analysis of events suggested infant-to-infant spread via the hands of personnel, but acquisition from the colonized staff was also possible. The control measures instituted prevented further spread of Ib/c-GBS in the NICU.