Selective suppression of interleukin-12 induction after macrophage receptor ligation.

Interleukin (IL)-12 is a monocyte- and macrophage-derived cytokine that plays a crucial role in both the innate and the acquired immune response. In this study, we examined the effects that ligating specific macrophage receptors had on the induction of IL-12 by lipopolysaccharide (LPS). We report that ligation of the macrophage Fcgamma, complement, or scavenger receptors inhibited the induction of IL-12 by LPS. Both mRNA synthesis and protein secretion were diminished to near-undetectable levels following receptor ligation. Suppression was specific to IL-12 since IL-10 and tumor necrosis factor-alpha (TNF-alpha) production were not inhibited by ligating macrophage receptors. The results of several different experimental approaches suggest that IL-12 downregulation was due to extracellular calcium influxes that resulted from receptor ligation. First, preventing extracellular calcium influxes, by performing the assays in EGTA, abrogated FcgammaR-mediated IL-12(p40) mRNA suppression. Second, exposure of macrophages to the calcium ionophores, ionomycin or A23187, mimicked receptor ligation and inhibited IL-12(p40) mRNA induction by LPS. Finally, bone marrow-derived macrophages from FcR gamma chain-deficient mice, which fail to flux calcium after receptor ligation, failed to inhibit IL-12(p40) mRNA induction. These results indicate that the calcium influxes that occur as a result of receptor ligation are responsible for inhibiting the induction of IL-12 by LPS. Hence, the ligation of phagocytic receptors on macrophages can lead to a dramatic decrease in IL-12 induction. This downregulation may be a way of limiting proinflammatory responses of macrophages to extracellular pathogens, or suppressing the development of cell-mediated immunity to intracellular pathogens.

Reversal of proinflammatory responses by ligating the macrophage Fcgamma receptor type I.

Macrophages can respond to a variety of infectious and/or inflammatory stimuli by secreting an array of proinflammatory cytokines, the overproduction of which can result in shock or even death. In this report, we demonstrate that ligation of macrophage Fcgamma receptors (FcgammaR) can lead to a reversal of macrophage proinflammatory responses by inducing an upregulation of interleukin (IL)-10, with a reciprocal inhibition of IL-12 production. IL-10 upregulation was specific to FcgammaR ligation, since the ligation of the Mac-1 receptor did not alter IL-10 production. The identification of the specific FcgammaR subtype responsible for IL-10 upregulation was determined in gene knockout mice. Macrophages from mice lacking the FcR gamma chain, which is required for assembly and signaling by FcgammaRI and FcgammaRIII, failed to upregulate IL-10 in response to immune complexes. However, mice lacking either the FcgammaRII or the FcgammaRIII were fully capable of upregulating IL-10 production, implicating FcgammaRI in this process. The biological consequences of FcgammaRI ligation were determined in both in vitro and in vivo models of inflammation and sepsis. In all of the models tested, the ligation of FcgammaR promoted the production of IL-10 and inhibited the secretion of IL-12. This reciprocal alteration in the pattern of macrophage cytokine production illustrates a potentially important role for FcgammaR-mediated clearance in suppressing macrophage proinflammatory responses.

Role of complement in mouse macrophage binding of Haemophilus influenzae type b.

Previous in vivo studies demonstrated that clearance of encapsulated Haemophilus influenzae from blood is associated with the deposition of C3 on these bacteria and is independent of the later complement components (C5-C9). Since clearance of encapsulated bacteria is determined by phagocytosis of bacteria by fixed tissue macrophages, we studied the interaction of H. influenzae type b with macrophages in vitro. Organisms bound to macrophages in the presence of nonimmune serum. Binding was not evident in heat-treated serum or in serum from complement depleted animals and was inhibited by F(ab')2 fragments of antibody to C3 and by blockade of the macrophage complement receptor type 3. The majority of organisms bound in the presence of complement alone remained extracellular. Antibody in the form of convalescent serum or an IgG1 monoclonal to type b capsule did not increase the total number of organisms associated with macrophages, but did increase the number of organisms ingested. Furthermore, complement enhanced antibody-mediated ingestion. This in vitro study demonstrates that complement largely mediates binding of H. influenzae to macrophages. This binding may be critical in determining the early clearance of these bacteria from blood and may be an important mechanism of defense in the nonimmune, as well as the immune host.

Clinical profile of ceftobiprole, a novel beta-lactam antibiotic.

Ceftobiprole, an investigational beta-lactam antibiotic, has been shown to have a broad spectrum of activity against Gram-positive and Gram-negative pathogens. Unlike currently available beta-lactams, ceftobiprole has been shown to be active against methicillin-resistant staphylococci because of its high affinity for penicillin-binding protein (PBP) 2' (2a). Ceftobiprole has undergone extensive evaluation in phase I studies to characterise dose, pharmacokinetics, and safety/tolerability. In an early phase II study, all 35 clinically evaluable patients (n = 40) with complicated skin and skin structure infections (cSSSIs) receiving intravenous ceftobiprole 750 mg twice-daily were cured, including four of four patients with methicillin-resistant Staphylococcus aureus (MRSA). Microbiological eradication was achieved in 91% (21/23) of evaluable patients. On the basis of these results, phase III studies of ceftobiprole for the treatment of cSSSIs were initiated. One study compared intravenous ceftobiprole (500 mg every 12 h) to intravenous vancomycin (1 g every 12 h) in patients with cSSSIs due to Gram-positive bacteria. Staphylococci were the predominant pathogens, and more than 25% of the microbiologically evaluable patients had infections caused by MRSA. In the clinically evaluable population, efficacy and adverse events were comparable between treatment arms. Additional clinical trials in cSSSI and pneumonia patients are underway to evaluate ceftobiprole for the treatment of infections due to both Gram-positive and Gram-negative bacteria. Ceftobiprole is the first cephalosporin to demonstrate clinical efficacy in patients with infections due to methicillin-resistant staphylococci and, if approved by regulatory authorities, is expected to be a useful addition to the armamentarium of agents for the treatment of complicated skin infections and pneumonia.

Energy balance, viral burden, insulin-like growth factor-1, interleukin-6 and growth impairment in children infected with human immunodeficiency virus.

OBJECTIVE: To determine the relationship between energy metabolism and growth abnormalities in HIV-infected children and to assess clinical or laboratory characteristics which may be contributing factors to their growth impairment. DESIGN: A comparative study. METHODS: We measured energy intake by inpatient calorie count/outpatient 24 h food recalls, resting energy expenditure by indirect calorimetry, total energy expenditure by the doubly-labeled water technique, iron metabolism, protein metabolism, and lipid metabolism markers as well as CD4 count, viral load, insulin-like growth factor-1 (IGF-1), serum interleukin-6 (IL-6), and whole blood stimulated IL-6 levels in prepubertal congenitally HIV-infected children with normal and impaired growth patterns. RESULTS AND CONCLUSIONS: Differences in energy expenditures were not found between normal and growth-impaired HIV-infected children. Energy intake but not energy expenditure was significantly reduced when HIV-infected children were compared to expected normal values for age and gender. Advanced HIV clinical disease, severe immune suppression, increased viral burden, increased IL-6 activity, decreased total serum protein, and decreased IGF-1 levels were more likely to be found in HIV-infected children with growth impairment in comparison with HIV-infected children with normal growth.

Staphylococcus epidermidis bacteremia in neonates: further observations and the occurrence of focal infection.

The frequency and clinical significance of Staphylococcus epidermidis isolates from blood cultures of neonates collected during a 17-month period in The New York Hospital neonatal intensive care unit (NICU) were reviewed. Twenty-three episodes of clinically significant S epidermidis bacteremia were detected using the criteria of isolation from 3/3 blood culture bottles from a single culture, or isolation from two or more blood cultures taken at different times, or simultaneous isolation from blood and fluid, pus or vascular catheter. Of these 23 episodes of S epidermidis bacteremia, ten were associated with colonized vascular catheters, and four episodes occurred in infants with necrotizing enterocolitis. Focal S epidermidis infection occurred in ten episodes, and persistent bacteremia occurred frequently in this setting. S epidermidis was the most frequent cause of bacteremia in the Neonatal Intensive Care Unit during the period reviewed. Of the isolates determined to be clinically significant, 74% were resistant to methicillin and cephalothin and 91% were resistant to gentamicin. All isolates were sensitive to vancomycin. In addition to removing vascular catheters suspected of being colonized and searching for potential sites of focal infection, an antibiotic regimen that includes vancomycin should be initiated once significant S epidermidis bacteremia has been recognized in the neonate.

Neonatal Staphylococcus epidermidis right-sided endocarditis: description of five catheterized infants.

Coagulase-negative staphylococci are important causes of bacteremia and focal infections in infants hospitalized in neonatal intensive care units. The medical records and echocardiograms of 58 newborns with persistent Staphylococcus epidermidis bacteremia who were hospitalized in the neonatal intensive care unit at The New York Hospital during the past 5 1/2 years were reviewed, and five infants were identified as having S epidermidis right-sided infective endocarditis. These episodes were associated with placement of umbilical venous catheters in the right atrium, slow resolution of bacteremia, and persistent thrombocytopenia. This experience suggests the role of endocardial trauma resulting from the placement of umbilical venous catheters in the pathogenesis of endocarditis. The increasing importance of coagulase-negative staphylococci as a cause of bacteremia in the newborn may explain the emergence of S epidermidis as an important cause of infective endocarditis in the neonatal intensive care unit. These cases underscore the potential severity of S epidermidis infection in the premature newborn.

Efficacy and safety of dapsone prophylaxis against Pneumocystis carinii pneumonia in human immunodeficiency virus-infected children.

Dapsone (4,4'-diaminodiphenylsulfone) is recommended as an alternative agent for prophylaxis against Pneumocystis carinii in children with human immunodeficiency virus infection. We reviewed our experience over the past 100 months with 20 children (age range, 2 months to 13 years) who received dapsone and examined the safety and efficacy of this regimen. Dapsone was taken for an average of 7.33 months/patient or a total of 4410 days by those children in whom safety could be assessed. Three of the 20 patients had an adverse reaction to dapsone. One had mild elevation of blood methemoglobin values (5.6%) and transient elevation of serum transaminases that resolved without discontinuing drug. The other two developed allergic skin rashes which necessitated discontinuation. Efficacy of dapsone in preventing P. carinii pneumonia (PCP) was assessed in 16 children at high risk for developing PCP (defined by CD4 counts or prior PCP infection). These 16 children took dapsone for an average of 6.88 months and a total of 3300 days. Two of the 16 high risk children, one who had had a previous P. carinii pneumonia, developed PCP while taking dapsone. Both had CD4 counts < or = 200 cells/mm3 and were taking dapsone for > or = 12 months before developing PCP. Dapsone is well-tolerated in children and appears to be as effective in preventing PCP in children with human immunodeficiency virus infection as it is in adults.

Anaerobic bacteremia in a neonatal intensive care unit: an eighteen-year experience.

A review of anaerobic bacteremia in the Neonatal Intensive Care Unit identified 29 episodes of clinically significant bacteremia occurring over the past 18 years. This experience suggested that certain clinical settings were associated with specific anaerobic infections. Although Gram-positive and Gram-negative anaerobes were isolated with similar frequency, 8 of 12 infants bacteremic within the first 48 hours of life were infected with Gram-positive, penicillin G-susceptible organisms whereas 11 of 17 infants older than 2 days were bacteremic with Gram-negative, penicillin G-resistant anaerobes. Eleven of 17 infants with anaerobic bacteremia associated with necrotizing enterocolitis were bacteremic with Gram-negative anaerobes. Five of 6 infants with anaerobic bacteremia associated with chorioamnionitis were bacteremic with Gram-positive anaerobes. These observations should be considered in making decisions regarding empiric therapy for the newborn at highest risk for anaerobic bacteremia.

Neonatal enterococcal bacteremia: an increasingly frequent event with potentially untreatable pathogens.

BACKGROUND: Enterococci can cause serious infections in the newborn. The increased number of these infections since the late 1970s and the increased isolation of organisms resistant to many commonly used antimicrobials prompted review of our experience with enterococcal bacteremia in the neonatal intensive care unit. This review was aimed at defining the character of illness of newborns who had these infections during a 20-year period. METHODS: This was a retrospective review of the medical records of newborns with enterococci isolated from blood. RESULTS: Between January, 1974, and December, 1993, 138 episodes of enterococcal bacteremia occurred in newborns hospitalized in the neonatal intensive care unit. Thirty-four episodes occurred during the first decade and 104 episodes during the second decade. One hundred of the 138 episodes were reviewed. In 64% of these episodes other microorganisms were also isolated from blood. Comparison of clinical characteristics associated with these episodes in the first and second decade demonstrated that episodes occurring in the more recent decade occurred in older infants (mean age of onset, 44.7 vs. 16.1 days; episodes occurring after 14 days, 73% vs. 41%). Common characteristics associated with enterococcal bacteremia included the presence of a central vascular catheter (77%), necrotizing enterocolitis (33%) and abdominal distension (21%). Vancomycin-resistant enterococci caused bacteremia in 6 infants and caused illnesses indistinguishable from those caused by susceptible organisms. CONCLUSIONS: In the more recent decade there were three times the number of episodes of enterococcal bacteremia in our neonatal intensive care unit than there were in the previous decade. The characteristics associated with these infections were similar to those occurring with other nosocomial bacterial infections in the neonate and did not change during the period reviewed. Most recent episodes occurred as part of polymicrobial infections in newborns hospitalized for more than 1 month. Infections caused by vancomycin-resistant enterococci occurred in older patients but were clinically indistinguishable from infections caused by sensitive organisms.

Characteristics of human immunodeficiency virus-infected children at the time of death: an experience in the 1990s.

OBJECTIVE: To describe the changes in the characteristics of human immunodeficiency virus (HIV)-related deaths in children with perinatally acquired infection. METHODS: A retrospective review of all deaths that occurred in HIV-infected children managed at The New York Hospital-Program for Children with AIDS during a 7-year period from January, 1990, to December, 1996. Differences in the characteristics at death between 15 children who died in 1990 and 10 children who died in 1996 were analyzed. RESULTS: Fifty-eight deaths in our cohort of HIV-infected children were identified during the 7-year period. The mean age at death was 4.43 years. Sixty-nine percent of children were black, 55% were male and 94% were receiving Medicaid. The mean weight/age Z score was -3.9 and the mean CD4 index was 0.067 with 65% having <50 CD4 cells/microl at the time of death (TOD). The most common organ/organ systems to be involved at the TOD were lung (78%) and central nervous system (61%). Mycobacterium avium complex (MAC) was the most common isolate at the TOD (26%) followed by Pneumocystis carinii (20%) and Pseudomonas aeruginosa (17%). The leading non-infectious cause of death was cardiac failure (9%). Comparison of the characteristics at the TOD between 1990 and 1996 revealed significant differences in mean age (2.1 vs. 9.2 years, P < 0.0001), mean CD4 count index (0.18 vs. 0.02, P < 0.03), mean number of organ/organ system involvement (3.9 vs. 5.9, P < 0.05), percent receiving antiretroviral therapy (33% vs. 70%, P < 0.02), mean number of years receiving antiretroviral therapy (0.88 vs. 3.86 years, P < 0.01), percent receiving P. carinii pneumonia prophylaxis (27% vs. 100%, P < 0.001), percent receiving MAC prophylaxis/therapy (0% vs. 100%, P < 0.0001), and cause of death from P. carinii pneumonia (53% vs. 0%, P < 0.01). CONCLUSIONS: Compared with children who died in 1990, HIV-infected children who died in 1996 were significantly older, more lymphopenic and more likely to have a greater number of organ system involvements and to have received antiviral therapy and antimicrobial prophylaxis. In 1996 no child died of P. carinii pneumonia. In 1996 MAC and P. aeruginosa were the two most important opportunistic infections causing death. These changes in the characteristics at death will warrant review of resources used in treating these children and may be critical in advising parents and care givers about the prognosis of this chronic infection.

Effect of changing antiretroviral therapy on human immunodeficiency virus viral load: experience with fifty-four perinatally infected children.

BACKGROUND: Experience in adults has shown that combination therapy including HIV protease inhibitors (PI) can profoundly affect viral replication and slow progression of HIV-associated disease. Trials defining the influence of PI and combination therapies on long term outcome of HIV infection in children have not yet been completed. Experience with infants and children who were receiving routine care in an HIV specialty clinic was reviewed to characterize the effect of changes involving one, two or three antiretrovirals. METHODS: Clinical and laboratory findings of children in whom antiretroviral therapy was changed were retrospectively reviewed. Successful response was defined as a reduction of viral load of at least 0.7 log10 RNA copies/ml lasting for at least 3 months. Differences in characteristics and the character of the response associated with successful and unsuccessful changes were analyzed. RESULTS: Of the 72 changes in therapy that were made in 54 children, 29 resulted in a successful response. A change involving 3 antiretrovirals was more likely to produce a successful response than a change involving 1 agent (6 of 9 vs. 6 of 24; P < 0.04). Reduction of viral load by > 100-fold or to undetectable amounts occurred more frequently in children who responded to a regimen containing a PI than in children who responded to reverse transcriptase inhibitors (11 of 21 vs. 1 of 8; P=0.05). Furthermore successful responses associated with addition of a PI were associated with a greater reduction in viral load than those that involved reverse transcriptase inhibitors (1.63+/-0.60 vs. 0.99+/-0.12 log10; P=0.003). CONCLUSIONS: This experience suggests that changing antiretroviral therapy in HIV-infected children to regimens containing three drugs is more likely to result in a successful virologic outcome than changes in therapy involving one drug. This experience further supports the conclusion that including a PI as part of an antiretroviral regimen is more likely to result in a greater reduction in viral load in children.

An investigation of vancomycin-resistant Enterococcus faecium within the pediatric service of a large urban medical center.

BACKGROUND: Between 1990 to 1992 and 1993 to 1995 there was a >5-fold increase (16.7% to 89.8%) in vancomycin-resistant Enterococcus faecium isolates as a percentage of all isolates of vancomycin-resistant enterococci on the pediatric units of The New York Hospital-Cornell Medical Center (NYH-CMC). A molecular epidemiologic investigation was undertaken to determine the extent to which this increase was associated with the spread of a vanA-containing clone of vancomycin-resistant E. faecium that had been previously defined in adults hospitalized at NYH-CMC or with the spread of another vanA clone that had been defined in children hospitalized on the pediatric service at Memorial Sloan-Kettering Cancer Center, which shares a common pediatric intensive care unit and pediatric house staff with NYH-CMC. METHODS: Molecular genotyping of vancomycin-resistant E. faecium isolates obtained from pediatric patients from 1993 to 1995 was performed by pulsed field gel electrophoresis of chromosomal SmaI digests. Southern hybridization was performed using vanA- and vanB-specific probes. Medical records of patients were reviewed for pertinent clinical and demographic information. RESULTS: A single vanB clone of vancomycin-resistant E. faecium was responsible for 17 (77.3%) of 22 isolates in the neonatal intensive care unit (NICU) of NYH-CMC. Two other vanB strains of vancomycin-resistant E. faecium and 2 vanA strains were identified among the 5 remaining NICU isolates. Vancomycin-resistant E. faecium isolates from the other pediatric units represented a heterogeneous population of primarily vanA strains, but vanA clonal strains previously identified from patients on adult services at NYH-CMC and from children hospitalized at Memorial Sloan-Kettering Cancer Center were not detected. CONCLUSION: A newly identified vanB clone was responsible for the increase in vancomycin-resistant E. faecium isolates in the NICU of NYH-CMC. The increase of vancomycin-resistant E. faecium among children hospitalized at NYH-CMC was unrelated to the spread of vancomycin-resistant E. faecium among adults in the same hospital or among children at an affiliated facility cared for by the same house staff and sharing a common pediatric intensive care unit.

Multiple methicillin-resistant Staphylococcus aureus strains as a cause for a single outbreak of severe disease in hospitalized neonates.

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of nosocomial infection. Outbreaks of infection caused by these pathogens are generally considered to be traceable to introduction of single strains into a hospital population. A large outbreak of bacteremic disease that recently occurred in our neonatal intensive care unit (11 episodes in 10 patients) involved 9 low birth weight infants and was associated with serious infection (4 episodes of meningitis). To determine the role of a single point source in this outbreak, isolates were characterized based on phenotypic and genotypic analyses. Phenotypic analysis included assessing hemolytic activity, phage typing, antimicrobial susceptibility testing and methicillin resistance population analysis. Genotypic analysis included assessment of plasmid profiles, dot-blot hybridization, restriction enzyme fragment pattern analysis and hybridization analysis of chromosomal DNA using a panel of staphylococcal gene probes. This analysis established that at least two distinct strains of MRSA were responsible for disease during this outbreak. This experience demonstrates the potential for MRSA to cause severe disease in the neonatal intensive care unit and indicates that the epidemiology of MRSA outbreaks is more complex than the spread of a single strain of bacteria.

Host defense abnormalities associated with HIV infection.

Infection with human immunodeficiency virus (HIV) impairs immune function. Most abnormalities in host defense associated with HIV infection are due to helper T-cell dysfunction. Studies defining these abnormalities in the HIV-infected patient have largely been done in adults. A more complete understanding of the immunodeficiency that occurs in infants and young children congenitally infected with HIV awaits further study of their immune function and the effect this virus has on the developing immune system.