ePoster Presentation 49th Annual Scientific Meeting of the Australian and New Zealand Society for Immunology 2021

Increased basal and induced phosphoinsitol-3-kinase signalling in B- and T-cells of healthy adults carrying the PTPN22 R620W mutations (#186)

Emily SJ Edwards 1 2 , Pei M Aui 1 2 , Julian J Bosco 2 3 , Samar Ojaimi 2 4 5 6 , Stephanie Stojanovic 2 3 , Josh Chatelier 2 3 , Robert G Stirling 2 3 , Paul U Cameron 2 3 , Fiona Hore-Lacy 2 3 , Robyn E O'Hehir 2 3 , Menno C van Zelm 1 2 3
  1. Immunology and Pathology, Monash University, Melbourne, VIC, Australia
  2. The Jeffrey Modell Diagnostic and Research Centre for Primary Immunodeficiencies in Melbourne, JMF, Melbourne, VIC, Australia
  3. Allergy, Asthma and Clinical Immunology Service, , Department of Respiratory, Allergy and Clinical Immunology (Research), The Alfred Hospital,, Melbourne, VIC, Australia
  4. Department of Infectious Diseases, Monash Health, Melbourne, VIC, Australia
  5. Centre for Inflammatory Diseases , Monash Health, Melbourne, VIC, Australia
  6. Department of Allergy and Immunology, Monash Health, Melbourne, VIC, Australia

Background: The non-synonymous common variant c.1858C>T (p.R620W) in PTPN22 is a risk variant for autoimmunity. Furthermore, prevalence is higher in patients with predominantly antibody deficiency (PAD), a primary immunodeficiency with increased incidence of autoimmunity. PTPN22 is a phosphatase that restricts signal transduction downstream of B- and T-cell receptors. Whether this mutation enhances or impairs PTPN22 function is currently disputed. Here, we addressed this by studying phosphoinositol-3-kinase (PI3K) signalling in B- and T-cells from healthy adults with and without the c.1858C>T variant.

Methods: Peripheral blood was collected from 63 healthy adults for Sanger sequencing for PTPN22 c.1858C>T variant identification, detailed B- and T-cell immunophenotyping, and in vitro stimulation of antigen receptor signalling for S6 phosphorylation.

Results: 6/63 healthy controls were heterozygous for PTPN22 c.1858C>T, at an allele frequency of 4.8%. Heterozygous carriers had significantly higher CD27+IgM+IgD+ B-cell numbers. Carriers expressed higher CD19 and lower CD21 levels on transitional and naïve-mature B-cells, and higher CD8 levels on cytotoxic T-cells. Additionally, their naïve B-, CD4+ and CD8+ T-cells exhibited higher basal phosphorylated-S6 levels. Finally, antigen receptor stimulation resulted in higher phospho-S6 levels in B-cells (anti-IgM) and T-cells (anti-CD3) compared to individuals without the variant.

Conclusion: Here, we showed for the first time that PTPN22 R620W results in increased PI3K signalling in B- and T-cells, demonstrating that the mutation inhibits the repressive function of PTPN22. PI3K signalling in lymphocytes is tightly balanced with increased activity resulting from PIK3CD and PIK3R1 mutations leading to antibody deficiency and autoimmunity. Our results indicate that this variant has similar effects but to a milder degree, which would explain the predisposition to autoimmunity. Thus, a common variant can directly impact an individual’s immune profile. Future studies, will address the functional consequences of this variant in PAD patients and whether this functions as a first genetic hit for developing disease.