B cells characterization in ADA2 Deficiency patients

Introduction

ADA2 deficiency, a recently described disease, is characterized by systemic vasculopathy and episodes of strokes. The defect is due to a loss of function mutation of CECR1 gene, codifying for Adenosine Deaminase 2 protein. This protein regulates the catabolism of extracellular adenosine, which we have recently shown is an important regulator of Class Switch Recombination in B lymphocytes. Accordingly DADA2 patients can present hypogammaglobulinemia.

Objectives

Therefore we decided to characterize peripheral B and T lymphocytes of DADA patients to directly address if ADA2 mutation affects B-cell function and in particular we focused on B cell- T cell interaction.

Patients and methods

3 patients carrying mutations in CECR1 were examined. They showed clinical history with livedo reticularis, fever, vasculitis and neurological symptoms. Two patients presented hypogammaglobulinemia requiring intravenous immunoglobulin replacement therapy. We analyzed peripheral B and T cell phenotype by flow cytometry, in vitro B-cell proliferation and differentiation to Immunoglobulin secreting cells in response to CpG and T cell help.

Results

Flow cytometer analysis showed a reduction of total B cells compared with age matched controls. Intriguingly a decrease in the percentage of memory B cell compartment (CD19+CD27+) was observed. Moreover we noted that the rate of B cells proliferation and differentiation to Immunoglobulin Secreting Cells of DADA2 patients with autologous T cell help are impaired. In fact in vitro IgM, IgG and IgA secretion is significantly reduced with respect to HD B lymphocytes in presence of mutated CD4 helper T cells.

Conclusions

Our findings suggest that ADA2 defect could lead to a defect in B cell function and to a reduced T cell dependent B cell response.