Abstract: TH-PO040

The Immunoglobulin Repertoire in IgA Nephropathy Revealed by Deep Sequencing

Session Information

Category: Glomerular

  • 1001 Glomerular: Basic/Experimental Immunology and Inflammation

Authors

  • Steers, Nicholas J., Columbia University, New York, New York, United States
  • Sheng, Zizhang, Columbia University, New York, New York, United States
  • Mccutchan, Jason, Columbia University, New York, New York, United States
  • Shapiro, Lawrence, Columbia University, New York, New York, United States
  • Gharavi, Ali G., Columbia University, New York, New York, United States
Background

Dysregulated IgA1 response is a central defect in the development of IgA nephropathy (IgAN), but it is not clear if the altered IgA1 response is attributable to a monoclonal or polyclonal expansion of the dysregulated of IgA plasma B-cells.

Methods

Our cohort consisted of 15 healthy controls (HC), 16 IgAN patients. IgA plasma cells were phenotyped by flow cytometry, IgA1, IgA, and IgG were measured by ELISA. The immunoglobulin repertoire was sequenced and analyzed using SONAR software.

Results

We studied peripheral B-cells in 16 IgAN patients, and 15 HC, in the steady state. Increased numbers of IgA plasma cells (88 per 1000 activated B-cells) were detected in the peripheral blood of IgAN patients compared to HC (20 per 1000 activated B-cells), correlating with increased levels of IgA and IgA1 detected in the plasma. Following in vitro stimulation, IgA cells from IgAN patients have a greater proliferative capacity compared to HC. We next asked if the increased number of peripheral IgA B-cells in IgAN patients arose by monoclonal or polyclonal expansion. We used NGS to sequence the immunoglobulin repertoire to determine if there were differences in usage of immunoglobulin heavy chain variable (V), heavy chain joining (J), kappa and lambda genes. We observed no differences in the heavy chain V, J and kappa usage, however we detected an enhanced usage of the IGLV2-8 lambda chain in IgAN patients compared to controls (12.9% Vs 7.9% respectively, p<0.01). Examination of the complementary determining region (CDR) 3 length or the somatic hypermutation (SHM) levels in the immunoglobulin sequences showed no differences between the IgAN patients and the HC.

Conclusion

We did not detect any consistent differences in usage of immunoglobulin heavy V and J chains, CDR3 length, or SHM levels between IgAN patients and HC at the repertoire level, with the exception of lambda IGLV2-8 usage. This indicates a global expansion of IgA plasma cells rather than a monoclonal expansion in IgA Nephropathy. Future studies will be directed towards identification of intrinsic and extrinsic regulatory factors leading to globally enhanced proliferative potential in IgA plasma cells.

Funding

  • NIDDK Support