Generation of switched memory B cells in response to vaccination in Down syndrome children and their siblings

BACKGROUND

Immunodeficiency is an integral aspect of Down syndrome, as demonstrated by the increased susceptibility to infection of affected. Mortality is still higher than in general population, with respiratory infections among the major causes of death. As more people with Down syndrome are living today than ever before, it is indispensable to develop strategies to prevent and cure the associated disorders. Vaccination is the most successful instrument of preventive medicine. Special seasonal influenza and pneumococcal vaccination strategies have been designed for individuals with risk conditions of all ages. Down syndrome individuals are not included in the high-risk categories.

METHODS

We enrolled in our study 15 children with Down syndrome and their siblings, vaccinated for the first time with seasonal influenza vaccine and receiving a booster dose of a glyco-conjugated pneumococcal vaccine. We compared the immunological features and response to vaccination measuring serum antibody titers and frequency of specific memory B cells.

RESULTS

We confirm that a severe reduction of switched memory B cells is always associated to Down syndrome. After primary vaccination Down syndrome children generate significantly less specific switched memory B cells than their siblings. The response to a booster dose of vaccine is instead comparable in both groups. The production of specific antibodies was equally effective in Down syndrome and controls both after primary and secondary immunization.

CONCLUSIONS

Down syndrome individuals should be considered a high risk group, because of their increased susceptibility to infection and reduced number of switched memory B cells. Tailored vaccination protocols are needed in order to reduce their burden of infections throughout life.

Immunophenotype Anomalies Predict the Development of Autoimmune Cytopenia in 22q11.2 Deletion Syndrome

BACKGROUND

Patients with 22q11.2 deletion syndrome (22q11.2DS) may develop severe thrombocytopenic purpura and hemolytic anemia. There are no reliable predictors for the development of hematologic autoimmunity (HA) in these patients.

OBJECTIVE

To describe the peculiar B and T subpopulation defects in patients with 22q11DS who have developed HA and test if these defects precede the development of HA.

METHODS

We performed a case-control multicenter study. Patients with HA were compared with a control population of 22q11.2DS without HA (non-HA). A complete immunological evaluation was performed at diagnosis and at the last follow-up including extensive T and B phenotypes.

RESULTS

Immunophenotype at the last follow-up was available in 23 HA and 45 non-HA patients. HA patients had significantly decreased percentage of naïve CD4⁺ cells (26.8% vs 43.2%, P = .003) and recent thymic emigrants (48.6% vs 80.5%, P = .046); decreased class-switched B cells (2.0% vs 5.9%, P = .04) and increased naive B cells (83.5% vs 71.4%, P = .02); increased CD16+/56+ both in absolute number (312 vs 199, P = .009) and percentage (20.0% vs 13.0%, P = .03). Immunophenotype was performed in 36 patients (11 HA and 25 non-HA) at diagnosis. Odds ratio (OR) of immune cytopenia were estimated for both CD4 naïve ≤30% (OR 14.0, P = .002) and switched memory B cells ≤2% (OR 44.0, P = .01). The estimated survival curves reached statistical significance, respectively, P = .0001 and P = .002.

CONCLUSIONS

Among patients with 22q11.2DS, those with HA have characteristic lymphocyte anomalies that appear considerably before HA onset. Systematic immunophenotyping of patients with 22q11.2DS at diagnosis is advisable for early identification of patients at risk for this severe complication.

Altered frequencies of memory B cells in new-onset systemic lupus erythematosus patients

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune disease, characterized by B cell hyperactivity and pathogenic autoantibodies formation. The objective of this study is to evaluate the distribution of B cell subsets in patients with SLE. We included patients with SLE followed in First Affiliated Hospital of Xi'an JiaoTong University, Xi'an, China. Flow cytometry was used to measure frequencies of B cell subsets, including memory B cells, switched memory B cells, non-switched memory B cells, double-negative memory B cells, and naïve B cells in 130 patients with SLE and 55 healthy controls. The different distributions of B cell subsets were further evaluated by their associations with disease activity and clinical manifestation. SLE patients showed significant alteration of B cell subsets, including lower frequency of non-switched memory B cells and higher double-negative memory B cells. The frequencies of B cell subsets also varied between new-onset SLE patients and chronic SLE patients. Frequencies of total memory B cells, switched memory B cells, and non-switched memory B cells were lower in new-onset SLE patients and frequency of naïve B cells was higher compared with healthy controls. Chronic SLE patients showed increased switched memory B cells and double-negative memory B cells. In addition, switched memory B cells and double-negative B cells were higher in patients with lupus nephritis (LN) regardless of disease activity. Our findings suggested that abnormalities of the B cell subsets homeostasis might contribute to the pathogenesis of SLE.

Evaluation of antibody response to polysaccharide vaccine and switched memory B cells in pediatric patients with inflammatory bowel disease

Background/Aims

Inflammatory bowel disease (IBD) is a chronic disease of the gastrointestinal tract, whose etiologies are still unknown. This study was performed to evaluate the humoral immune response in terms of B cell functions in selected IBD patients.

Methods

Eighteen pediatric patients with IBD, including 12 cases of ulcerative colitis (UC) and six with Crohn disease (CD), were enrolled in this study. The pneumococcal vaccine was injected in all patients, and the IgG antibody level to the polysaccharide antigen was measured before and 4 weeks after injection. The B cell switch-recombination process was evaluated.

Results

Five patients with IBD (three CD and two UC) had defects in B cell switching, which was significantly higher than in controls (p=0.05). Ten patients had a specific antibody deficiency and exhibited a higher frequency of bacterial infection than the healthy group. The mean increased level of IgG after vaccination was lower in IBD patients (82.9±32.5 µg/mL vs 219.8±59.0 µg/mL; p=0.001). Among the patients who had an insufficient response, no significant difference in the number of switched memory B-cell was observed.

Conclusions

A defect in B lymphocyte switching was observed in pediatric IBD patients, and especially in those patients with CD. Owing to an increased risk of bacterial infections in those patients with antibody production defects, pneumococcal vaccination could be recommended. However, not all patients can benefit from the vaccination, and several may require other prophylactic methods.

Switched memory B cells promote alveolar bone damage during periodontitis: An adoptive transfer experiment

Periodontitis is a bacteria-induced disease that often leads to alveolar bone damage. We sought to determine the role and mechanism of switched memory B cells in alveolar bone destruction during periodontitis. Sensitized B cells were sorted and cultured, then their expression of receptor activator for nuclear factor-κB ligand (RANKL), interleukin-6 (IL-6), and interleukin-12 (IL-12) was detected. Using these cells, we prepared adoptive transfer models in which we induced periodontitis. We found that switched memory B cells produced more RANKL in terms of both protein and mRNA levels than other subpopulations. Switched memory B cells expressed more IL-6 and IL-12 mRNA than other subpopulations, but differences in respective protein levels were not significant. Moreover, we found that switched memory B cell transfer resulted in increased alveolar bone loss and periodontal osteoclastogenesis. Moreover, switched memory B cell transfer increased the proportion of Th1 and Th17 cells as well as the expression of RANKL, osteoprotegerin (OPG), tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), IL-1β, IL-6, IL-17A in gingiva, and cervical lymph nodes (CLNs). The outcomes of the present study indicate that switched memory B cells regulate alveolar bone homeostasis via enhancing cytokine expression and increasing proliferation of Th1 and Th17 cells.

B-cell subsets imbalance and reduced expression of CD40 in ataxia-telangiectasia patients

BACKGROUND

Ataxia-telangiectasia (AT) is a well-known primary immunodeficiency with recurrent sinopulmonary infections and variable abnormalities in both the humoral and cellular immune system. Dysfunctions in immunoglobulin production, reduced number of B cells, and B-cell receptor excision circles copies have been reported. We aimed to understand the immunological mechanisms involving the humoral compartment in AT patients by analysing peripheral blood B cells subsets, B-T lymphocyte cooperation through the expression of CD40 and CD40 ligand (CD40L), and cytokines involved in class-switch recombination production.

METHODS

We compared the proportion of B-cell subsets, the expression of CD40/CD40L, and the plasma levels of IL-6 and IFN-γ of 18 AT patients and 15 healthy age-sex-matched controls using flow cytometry.

RESULTS

We found that some steps in peripheral B cell development were altered in AT with a pronounced reduction of cell-surface CD40 expression. The proportions of transitional and naïve-mature B cells were reduced, whereas CD21-low, natural effector memory, IgM-only memory, and IgG atypical memory B cells were present in a higher proportion.

CONCLUSIONS

These findings revealed a disturbed B-cell homeostasis with unconventional maturation of B lymphocyte memory cells, which can explain the consequent impairment of humoral immunity.

Rapid isolation of a potent human antibody against H7N9 influenza virus from an infected patient

Influenza virus A H7N9 remains a serious threat to public health due to the lack of effective vaccines and drugs. In this study, a neutralizing human antibody named 3L11 was rapidly isolated from the switched memory B cells of a patient infected with H7N9. The antibody 3L11 was encoded by the heavy-chain VH1-8 gene and the light-chain VL2-13 gene that had undergone somatic mutations, and conferred high affinity binding to H7N9 hemagglutinins (HAs). It promoted killing of infected cells by antibody-dependent cell-mediated cytotoxicity (ADCC). Epitope mapping by mass spectroscopy (MS) indicated that 3L11 bound to the peptide 149-175 of HAs that contained the 150-loop of the receptor-binding site (RBS). Additionally, the 3L11 escape strains had G151R (Gly¹⁵¹→Arg¹⁵¹) and S152P (Ser¹⁵²→Pro¹⁵²) mutations within a conserved antigenic site A near the RBS that were not observed in field strains. Importantly, 3L11 fully protected mice against a lethal H7N9 virus challenge, in both pre- and postexposure administration regimens. Altogether, this work demonstrates the feasibility of rapid isolation of neutralizing H7N9 antibodies from infected patients and provides a potential prophylactic and therapeutic agent against H7N9 viruses.