Immunobiology of Primary Antibody Deficiencies: Towards a new classification

Primary antibody deficiencies (PADs) are the most common primary immunodeficiencies. The hallmark of PADs is a defect in the production of normal amounts of antigen specific antibodies. These antibodies or immunoglobulins are indispensible for the adaptive immune response against a wide variety of pathogens. A defect in antibody production results in recurrent and/or severe infections. PADs represent a heterogeneous spectrum of conditions, ranging from often asymptomatic selective IgA and IgG subclass deficiencies to the severe congenital agammaglobulinemia’s, in which antibody production of all immunoglobulin isotypes is severely decreased. Apart from recurrent infections there is a wide range of other clinical complications associated with primary antibody deficiency, affecting quality of life and life expectancy. Primary antibody deficiencies are the result of primary or secondary defects in B-cell development. This Chapter will discuss the principles of adaptive immunity including normal B-cell development, followed by an introduction of the known immunogenetic and clinical characteristics of primary antibody deficiency. Next, we give an overview of potential pathophysiological mechanism in idiopathic primary immunodeficiency. Finally, the aims of the thesis are explained

Circadian variation of plasminogen-activator-inhibitor-1 levels in children with meningococcal sepsis

Objective To study whether the circadian variation of plasminogen-activator-inhibitor-1 (PAI-1) levels, with high morning levels, is associated with poor outcome of children with meningococcal sepsis presenting in the morning hours. Design Retrospective analysis of prospectively collected clinical and laboratory data. Setting Single center study at Erasmus MC-Sophia Children's Hospital, Rotterdam, the Netherlands. Subjects 184 patients aged 3 weeks to 18 years with meningococcal sepsis. In 36 of these children, PAI-1 levels at admission to the PICU were measured in plasma by ELISA. Interventions None. Measurements and main results Circadian variation was studied by dividing one day in blocks of 6 hours. Patients admitted between 6:00 am and 12:00 am had increased illness severity scores and higher PAI-1 levels (n = 9, median 6912 ng/mL, IQR 5808-15600) compared to patients admitted at night (P = 0.019, n = 9, median 3546 ng/mL, IQR 1668-6118) or in the afternoon (P = 0.007, n = 7, median 4224 ng/mL, IQR 1804-5790). In 184 patients, analysis of circadian variation in relation to outcome showed more deaths, amputations and need for skin grafts in patients admitted to the PICU between 6:00 am and 12:00 am than patients admitted during the rest of the day (P = 0.009). Conclusions Circadian variation of PAI-1 levels is present in children with meningococcal sepsis and is associated with illness severity, with a peak level in the morning. Whether circadian variation is an independent risk factor for morbidity and mortality in meningococcal sepsis needs to be explored in future studies

The 11q Terminal Deletion Disorder Jacobsen Syndrome is a Syndromic Primary Immunodeficiency

Background: Jacobsen syndrome (JS) is a rare contiguous gene syndrome caused by partial deletion of the long arm of chromosome 11. Clinical features include physical and mental growth retardation, facial dysmorphism, thrombocytopenia, impaired platelet function and pancytopenia. In case reports, recurrent infections and impaired immune cell function compatible with immunodeficiency were described. However, Jacobsen syndrome has not been recognized as an established syndromic primary immunodeficiency. Goal: To evaluate the presence of immunodeficiency in a series of 6 patients with JS. Methods: Medical history of 6 patients with JS was evaluated for recurrent infections. IgG, IgA, IgM and specific antibodies against S. pneumoniae were measured. Response to immunization with a polysaccharide vaccine (Pneumovax) was measured and B and T lymphocyte subset analyses were performed using flowcytometry. Results: Five out of 6 patients suffered from recurrent infections. These patients had low IgG levels and impaired response to S. pneumoniae polysaccharide vaccination. Moreover, we also found a significant decrease in the absolute number of memory B cells, suggesting a defective germinal center function. In a number of patients, low numbers of T lymphocytes and NK cells were found. Conclusions: Most patients with JS suffer from combined immunodeficiency in the presence of recurrent infections. Therefore, we consider JS a syndromic primary immunodeficiency. Early detection of immunodeficiency may reduce the frequency and severity of infections. All JS patients should therefore undergo immunological evaluation. Future studies in a larger cohort of patients will more precisely define the pathophysiology of the immunodeficiency in JS

Immunoglobulin G fragment crystallizable glycosylation after hematopoietic stem cell transplantation is dissimilar to donor profiles

Immunoglobulin G (IgG) fragment crystallizable (Fc) N-glycosylation has a large influence on the affinity of the antibody for binding to Fcγ-receptors (FcγRs) and C1q protein, thereby influencing immune effector functions. IgG Fc glycosylation is known to be partly regulated by genetics and partly by stimuli in the microenvironment of the B cell. Following allogeneic hematopoietic stem cell transplantation (HSCT), and in the presence of (almost) complete donor chimerism, IgG is expected to be produced by, and glycosylated in, B cells of donor origin. We investigated to what extent IgG glycosylation in patients after transplantation is determined by factors of the donor (genetics) or the recipient (environment). Using an IgG subclass-specific liquid chromatography-mass spectrometry method, we analyzed the plasma/serum IgG Fc glycosylation profiles of 34 pediatric patients pre-HSCT and at 6 and 12 months post-HSCT and compared these to the profiles of their donors and age-matched healthy controls. Patients treated for hematological malignancies as well as for non-malignant hematological diseases showed after transplantation a lower Fc galactosylation than their donors. Especially for the patients treated for leukemia, the post-HSCT Fc glycosylation profiles were more similar to the pre-HSCT recipient profiles than to profiles of the donors. Pre-HSCT, the leukemia patient group showed as distinctive feature a decrease in sialylation and in hybrid-type glycans as compared to healthy controls, which both normalized after transplantation. Our data suggest that IgG Fc glycosylation in children after HSCT does not directly mimic the donor profile, but is rather determined by persisting environmental factors of the host

Overview of 15-year severe combined immunodeficiency in the Netherlands: towards newborn blood spot screening

Severe combined immune deficiency (SCID) is a fatal primary immunodeficiency usually presenting in the first months of life with (opportunistic) infections, diarrhea, and failure to thrive. Hematopoietic stem cell transplantation (HSCT) and gene therapy (GT) are curative treatment options. The objective of the study was to assess the morbidity, mortality, and diagnostic and therapeutic delay in children with SCID in the Netherlands in the last 15 years. These data may help to judge whether SCID should be considered to be included in our national neonatal screening program. In the period 1998–2013, 43 SCID patients were diagnosed in the Netherlands, 11 of whom were atypical SCID (presentation beyond the first year). The median interval between the first symptom and diagnosis was 2 months (range 0–1173 months). The total mortality was 42 %. In total, 32 patients were treated with HSCT of whom 8 were deceased. Nine patients died due to severe infectious complications before curative treatment could be initiated. Conclusion: Because of a high mortality of patients with SCID before HSCT could be initiated, only a national newborn screening program and pre-emptive HSCT or GT will be able to improve survival of these patients

Exhaustion of the CD8+ T cell compartment in patients with mutations in phosphoinositide 3-kinase delta

Pathogenic gain-of-function mutations in the gene encoding phosphoinositide 3-kinase delta (PI3Kδ) cause activated PI3Kδ syndrome (APDS), a disease characterized by humoral immunodeficiency, lymphadenopathy, and an inability to control persistent viral infections including Epstein-Barr virus (EBV) and cytomegalovirus (CMV) infections. Understanding the mechanisms leading to impaired immune response is important to optimally treat APDS patients. Immunosenescence of CD8+ T cells was suggested to contribute to APDS pathogenesis. However, the constitutive activation of T cells in APDS may also result in T cell exhaustion. Therefore, we studied exhaustion of the CD8+ T cell compartment in APDS patients and compared them with healthy controls and HIV patients, as a control for exhaustion. The subset distribution of the T cell compartment of APDS patients was comparable with HIV patien

A novel heterozygous mutation in the STAT1 SH2 domain causes chronic mucocutaneous candidiasis, atypically diverse infections, autoimmunity, and impaired cytokine regulation

Chronic mucocutaneous candidiasis (CMC) is a primary immunodeficiency characterized by persistent or recurrent skin and mucosal surface infections with Candida species. Different gene mutations leading to CMC have been identified. These include various heterozygous gain-of-function (GOF) mutations in signal transducer and activator of transcription 1 (STAT1) that are not only associated with infections but also with autoimmune manifestations. Recently, two STAT1 GOF mutations involving the Src homology 2 (SH2) domain have been reported, while so far, over 50 mutations have been described mainly in the coiled coil and the DNA-binding domains. Here, we present two members of a Dutch family with a novel STAT1 mutation located in the SH2 domain. T lymphocytes of these patients revealed STAT1 hyperphosphorylation and higher expression of STAT1 target genes. The clinical picture of CMC in our patients could be explained by diminished production of interleukin (IL)-17 and IL-22, cytokines important in the protection against fungal infections

Translating Sepsis-3 criteria in children: Prognostic accuracy of age-adjusted quick SOFA score in children visiting the emergency department with suspected bacterial infection

Background: Recent attempts to translate Sepsis-3 criteria to children have been restricted to PICU patients and did not target children in emergency departments (ED). We assessed the prognostic accuracy of the age-adjusted quick Sequential Organ Failure Assessment score (qSOFA) and compared the performance to SIRS and the quick Pediatric Logistic Organ Dysfunction-2 score (qPELOD-2). We studied whether the addition of lactate (qSOFA-L) would increase prognostic accuracy. Methods: Non-academic, single-center, retrospective study in children visiting the ED and admitted with suspected bacterial infection between March 2013 and January 2018. We defined suspected bacterial infection as initiation of antibiotic therapy within 24 h after ED entry. Age-adjusted qSOFA, SIRS, qPELOD-2, and qSOFA-L scores were compared by area under the receiver operating characteristics curve (AUROC) analysis. Primary outcome measure was PICU transfer and/or mortality and secondary outcome was prolonged hospital length of stay. Results: We included 864 ED visits [474 (55%) male; median age 2.5 years; IQR 9 months-6 years], of which 18 were transferred to a PICU and 6 ended in death [composite outcome PICU transfer and/or mortality; 23 admissions (2.7%)]. 179 (22.2%) admissions resulted in prolonged hospital length of stay. PICU transfer and/or death was present in 22.5% of visits with qSOFA≥2 (n = 40) compared to 2.0% of visits with qSOFA < 2 (n = 444) (p < 0.01). qSOFA tends to be the best predictor of PICU transfer and/or mortality (AUROC 0.72 (95% CI, 0.57-0.86) compared to SIRS [0.64 (95% CI, 0.53-0.74), p = 0.23] and qPELOD-2 [0.60 (95% CI, 0.45-0.76), p = 0.03)]. Prolonged hospital length of stay was poorly predicted by qSOFA (AUROC 0.53, 95% CI 0.46-0.59), SIRS (0.49, 95% CI 0.44-0.54), and qPELOD-2 (0.51, 95%CI 0.45-0.57). qSOFA-L resulted in an AUROC of 0.67 (95%CI, 0.50-0.84) for PICU transfer and/ormortality and an AUROC of 0.56 (95% CI, 0.46-0.67) for prolonged hospital length of stay. Conclusion: The currently proposed bedside risk-stratification tool of Sepsis-3 criteria, qSOFA, shows moderate prognostic accuracy for PICU transfer and/or mortality in children visiting the ED with suspected bacterial infection. The addition of lactate did not improve prognostic accuracy. Future prospective studies in larger ED populations are needed to further determine the utility of the qSOFA score

Target attainment of cefotaxime in critically ill children with meningococcal septic shock as a model for cefotaxime dosing in severe pediatric sepsis

Reduced target attainment of β-lactam antibiotics is reported in critically ill patients. However, as target attainment of cefotaxime in severely ill pediatric sepsis patients may differ from adults due to age-related variation in pharmacokinetics, we aimed to assess target attainment of cefotaxime in this pilot study using meningococcal septic shock patients as a model for severe sepsis. Secondary analysis of prospectively collected data from a randomized controlled trial. Children with meningococcal septic shock (1 month to 18 years) included in this study received cefotaxime 100–150 mg/kg/day as antibiotic treatment. Left-over plasma samples were analyzed using LC-MS/MS to determine cefotaxime concentrations. MIC values from EUCAST were used to determine target attainment of cefotaxime for Neisseria meningitidis (0.125 mg/l), but also for Streptococcus pneumoniae (0.5 mg/l), Enterobacteriaceae (1 mg/l), and Staphylococcus aureus (4 mg/l). Target attainment was adequate when all samples exceeded MIC or fourfold MIC values. One thirty-six plasma samples of 37 severe septic shock patients were analyzed for cefotaxime concentrations. Median age was 2 years with a median PRISM-score of 24 and mortality of 24.8%. The median unbound cefotaxime concentration was 4.8 mg/l (range 0–48.7). Target attainment ranged from 94.6% for the MIC of N. meningitidis to 16.2% for fourfold the MIC S. aureus. Creatinine levels were significantly cor

Evaluation of a clinical decision rule to guide antibiotic prescription in children with suspected lower respiratory tract infection in The Netherlands

BACKGROUND: Optimising the use of antibiotics is a key component of antibiotic stewardship. Respiratory tract infections (RTIs) are the most common reason for antibiotic prescription in children, even though most of these infections in children under 5 years are viral. This study aims to safely reduce antibiotic prescriptions in children under 5 years with suspected lower RTI at the emergency department (ED), by implementing a clinical decision rule. METHODS AND FINDINGS: In a stepped-wedge cluster randomised trial, we included children aged 1-60 months presenting with fever and cough or dyspnoea to 8 EDs in The Netherlands. The EDs were of varying sizes, from diverse geographic and demographic regions, and of different hospital types (tertiary versus general). In the pre-intervention phase, children received usual care, according to the Dutch and NICE guidelines for febrile children. During the intervention phase, a validated clinical prediction model (Feverkidstool) including clinical characteristics and C-reactive protein (CRP) was implemented as a decision rule guiding antibiotic prescription. The intervention was that antibiotics were withheld in children with a low or intermediate predicted risk of bacterial pneumonia (≤10%, based on Feverkidstool). Co-primary outcomes were antibiotic prescription rate and strategy failure. Strategy failure was defined as secondary antibiotic prescriptions or hospitalisations, persistence of fever or oxygen dependency up to day 7, or complications. Hospitals were randomly allocated to 1 sequence of treatment each, using computer randomisation. The trial could not be blinded. We used multilevel logistic regression to estimate the effect of the intervention, clustered by hospital and adjusted for time period, age, sex, season, ill appearance, and fever duration; predicted risk was included in exploratory analysis. We included 999 children (61% male, median age 17 months [IQR 9 to 30]) between 1 January 2016 and 30 September 2018: 597 during the pre-intervention phase and 402 during the intervention phase. Most children (77%) were referred by a general practitioner, and half of children were hospitalised. Intention-to-treat analyses showed that overall antibiotic prescription was not reduced (30% to 25%, adjusted odds ratio [aOR] 1.07 [95% CI 0.57 to 2.01, p = 0.75]); strategy failure reduced from 23% to 16% (aOR 0.53 [95% CI 0.32 to 0.88, p = 0.01]). Exploratory analyses showed that the intervention influenced risk groups differently (p < 0.01), resulting in a reduction in antibiotic prescriptions in low/intermediate-risk children (17% to 6%; aOR 0.31 [95% CI 0.12 to 0.81, p = 0.02]) and a non-significant increase in the high-risk group (47% to 59%; aOR 2.28 [95% CI 0.84 to 6.17, p = 0.09]). Two complications occurred during the trial: 1 admission to the intensive care unit during follow-up and 1 pleural empyema at day 10 (both unrelated to the study intervention). Main limitations of the study were missing CRP values in the pre-intervention phase and a prolonged baseline period due to logistical issues, potentially affecting the power o