THU0030 DISTINCT EFFECTS OF FIVE JAK INHIBITORS IN THE MODULATION OF HUMAN B CELL ACTIVATION

Background:

JAK inhibitors have been successfully introduced in the treatment of rheumatoid arthritis (RA) and psoriatic arthritis and are in clinical trials for numerous other autoimmune diseases. JAK inhibition effectively reduces cytokine-mediated activation and survival of pathology-driving immune cells by targeting signaling downstream of cytokine receptors. The outcome of such immunomodulation hence will largely depend on the intrinsic expression of the four different JAKs, the cytokine environment and the targeted cell type. Comparative studies investigating the effect on B cells are lacking. In light of the use of JAK inhibitor treatment in autoantibody mediated diseases, the study of the B cell compartment represents a milestone to assess their potential.

Objectives:

We thus aimed to study the B cell compartment as well as B cell function under JAK inhibition in RA patients and to compare the specific effect the JAK inhibitors tofacitinib (pan-JAK), baricitinib (JAK1/2), ruxolitinib (JAK1/2), upadacitinib and filgotinib (selective JAK1) on in vitro B cell activation, differentiation, proliferation, and class switch.

Methods:

B cell subpopulations in RA patients treated with baricitinib or tofacitinib was assessed by flow cytometric analysis of peripheral blood mononuclear cells. For in vitro studies, magnetically isolated total B cells from healthy donors were stimulated T-cell -independently with CpG and treated with scalar doses of the JAK inhibitors tofacitinib, baricitinib, ruxolitinib, upadacitinib and filgotinib. Flow cytometric analysis was performed on days 0, 3 and 6. Cytokine secretion was measured by Cytokine Multiplex Assay.

Results:

B cell phenotyping of RA patients treated with JAK inhibitors baricitinib or tofacitinib showed an increase in marginal zone (MZ) B cells. To investigate this further, we turned to an in vitro model of T-cell-independent B cell activation with CpG via TLR9, known to support MZ B cell expansion. Here, JAK1/2 and selective JAK1 inhibitor treatment led to a dose-dependent decrease of total B cell numbers. When assessing B cell-subpopulations, we observed an altered B cell differentiation with a significant increase in MZ-like B cells under JAK inhibition, which led to a subsequent increase in plasmablast differentiation in the first days. This effect was more pronounced upon pan-JAK inhibitor treatment than JAK1 or JAK1/2 inhibition, indicating that broader JAK inhibition is associated with a stronger effect (tofa > ruxo > bari > upa > filgo).

Notably, we further detected a significant dose-dependent reduction of switched memory formation, strongest with JAK1/2 inhibition (upa > ruxo > bari > tofa > filgo). Consistent with this finding, we observed decreased AID expression under JAK inhibition. Concomitantly, induction of STAT3 expression and STAT3 phosphorylation were reduced under JAK inhibition, suggesting that downstream signalling was abrogated.

To assess the role of autocrine signaling in this system, we measured cytokine secretion upon JAK inhibition and found that JAK2 inhibition led to reduced IL10 secretion. This in turn resulted in an increase of inflammatory cytokines such as IL6, TNF, highlighting the importance of B cell as cytokine-secreting cell type.

Conclusion:

In a T-independent in vitro B cell model JAK inhibition led to a reduced total B cell number as well as reduced switched memory development, whereas MZ-like B cells were increased. Especially JAK2 inhibition strongly impaired switched memory formation. JAK inhibition does not only impact cytokine signalling but also leads to changes in cytokine secretion dynamics and amounts, potentially impacting other cell types.

In conclusion, JAK inhibition has a major effect on B cell activation and maturation, with differential outcomes between JAK inhibitors hinting towards distinct and unique effects on B cell homeostasis.

Disclosure of Interests:

None declared

AB0033 CHARACTERIZATION OF THE PERIPHERAL B CELL COMPARTMENT IN PATIENTS WITH EOSINOPHILIC GRANULOMATOSIS WITH POLYANGIITIS

Background:

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare form of systemic vasculitis, which is characterized by bronchial asthma, hypereosinophilia, and systemic vasculitis. B-lymphocytes play a key role in EGPA as producers of IgE and anti-neutrophil cytoplasmic antibodies (ANCAs). Indeed, the neutrophils that are targeted by these antibodies are widely described as the mechanism of endothelial damage in this disease. On the other side, the therapeutic response to rituximab in EGPA patients provides evidence for a role of B-cells in the pathogenesis of EGPA. Therefore characterizing B cell subpopulations may help in understanding the disease and the treatment.

Objectives:

To characterize the peripheral B cell compartment in patients with EGPA and to analyze the in vivo potential of B lymphocytes to class-switch to IgE and to assess in vitro the differentiation potential of naïve B cells of EGPA patients into IgE-secreting plasmablasts.

Methods:

Clinical characteristics of the patients, including organ involvement and treatment regimen were evaluated. Laboratory work-up included ANCA-status, eosinophils, IgE, IgG, IgA, IgM, and peripheral CD19+B-cell count. For immunophenotyping isolated PBMCs were stained with monoclonal or polyclonal antibodies and B cells were classified into: naïve, marginal zone, class-switched memory B cells, unconventional memory B cells, transitional and plasmablasts. Furthermore, the expression of IgG+ and subclasses IgG1-4, IgA+, IgE+B cells, BAFFR and TACI was quantified. For in vitro differentiation assays magnetically isolated B lymphocytes from EGPA patients and age-matched healthy controls were stimulated with CD40L, IL-21 and IL-4. Starting the culture with equal number of B cells, the absolute number of plasmablasts, and IgE class switched cells after 9 days was determined by counting the events in the CD27highCD38high gate or the IgG/A/D-IgE+gate by flow cytometry. IgE secretion in the supernatant was measured by ELISA. JAK-STAT signalling pathway was analyzed in response to IL-4 and IL-21 stimulation and phosphorylation of STAT5 and 6 measured by flow cytometry.

Results:

34 patients with EGPA diagnosed according to ACR and CHC-criteria were included into the study. Ten of these patients were analysed separately because they received rituximab therapy. Peripheral B cell numbers in EGPA patients were markedly diminished. B cell subpopulation phenotyping showed in average 57.9% naïve B cells, 12.5 % marginal zone like B cells and 19.2% switched memory B cells. Plasmablasts constituted in average 1.15% of the peripheral B cell compartment, transitional B cells 2.0%. Interestingly, the expression of BAFF receptor and TACI in the memory B cell subset was significantly decreased in EGPA patients when compared with healthy donors. In vitro assays of isolated B cells from EGPA patients demonstrated an increased proportion of IgE-class-switched B cells after 9 days of culture under IL4 stimulation compared with controls. However, no differences were observed in the phosphorylation of STAT5 and STAT6 after stimulation with IL-4 or IL-21.

Conclusion:

In the EGPA-patients we observed markedly diminished B-cells despite of normal lymphocyte counts. B cells showed a reduced expression of BAFF-R and TACI. Class switch to IgE is enhanced in EGPA patients.

Disclosure of Interests:

None declared

Vav1 haploinsufficiency in a common variable immunodeficiency patient with defective T-cell function

Common variable immunodeficiency (CVID) is a primary immune disorder characterized by impaired antibody production, which is in many instances secondary to defective T cell function (T-CVID). We previously identified a subset of T-CVID patients characterized by defective expression of Vav1, a guanine nucleotide exchanger which couples the T-cell antigen receptor to reorganization of the actin cytoskeleton. Here we have addressed the possibility that an intrinsic defect in the Vav1 gene might underlie the reduction in Vav protein observed in T cells from these patients. We report the identification in one T-CVID patient of a heterozygous deletion in Vav1. The gene deletion, spanning exons 2-27, accounts for the reduction in Vav1 mRNA and protein in T cells from this patient. The disease-related pedigree of this patient suggests a de novo origin of the Vav1 deletion. The findings highlights Vav1 as an autosomal dominant disease gene associated with CVID with defective T-cell function.

Significant bacteriuria in outpatient diabetic and non-diabetic persons

AIMS

The prevalence of significant bacteriuria (SB) in diabetes mellitus has not been clearly established. Having previously investigated SB frequency in inpatient diabetic women, we now screened for SB (both asymptomatic and symptomatic forms) in outpatients.

METHODS

We examined 511 consecutive outpatients with Type 1 (T1D) or Type 2 diabetes (T2D), and 98 non-diabetic subjects. At least one uncontaminated midstream urine sample was available from 602 subjects: 64 T1D (37 female, age 49 +/- 13 years, diabetes duration 23 +/- 15 years), 441 T2D (212 female, 66 +/- 10 years, 12 +/- 10 years), and 97 healthy control subjects (39 female, 57 +/- 12 years). On the same day, we determined: blood cell count, fasting plasma glucose (FPG), glycated haemoglobin (HbA(1c)), plasma creatinine, urinary creatinine, and urinary albumin excretion (UAE; microg/mg urinary creatinine).

RESULTS

The rate of SB was 14.1% in T1D, 9.3% in T2D and 6.2% in control subjects (P = NS). The 50 diabetic patients with SB differed from the 455 diabetic patients without SB in gender (43 male vs. 206 female, P < 0.001), FPG (10.2 +/- 3.6 vs. 9.2 +/- 2.9 mmol/l, P < 0.05), HbA(1c) (7.8 +/- 1.1 vs. 7.5 +/- 1.3%, P < 0.05), and UAE (median 15.6 vs. 7.6 microg/mg, P < 0.01). Eleven diabetic patients with SB had symptoms (vs. 48 without SB, P < 0.05); UAE levels were higher in the 39 asymptomatic diabetic patients with SB than in the 11 symptomatic patients.

CONCLUSIONS

The prevalence of SB is similar in outpatient diabetic individuals and in non-diabetic subjects. The main risk factors for SB in diabetic patients were female gender and UAE. The likelihood of asymptomatic SB increased with UAE levels, i.e. with the presence of established microangiopathy. Poor glycaemic control is associated with bacteriuria, either as a cause or consequence of bacteriuria.

[Pneumothorax in severe chest injuries]

The authors reviewed CT scans and supine chest X-ray of 47 patients affected by severe thoracic trauma, examined in 1985-86. The sensibility of the two methodologies in the assessment of pneumothorax was compared. CT detected 25 pneumothorax, whereas supine chest X-ray allowed a diagnosis in 18 cases only. In 8 of the latter (44.4%) the diagnosis was made possible by the presence of indirect signs of pneumothorax only--the most frequent being the deep sulcus sign. The characterization of pneumothorax is important especially in the patients who need to be treated with mechanical ventilation therapy, or who are to undergo surgery in total anaesthesia.