Analysis of SNARE-mediated regulation of plasma cell biology – PC-SEC

This project is based on a mouse model lacking Sec22b expression specifically in the B cell lineage. We use it to analyse the impact of Sec22b on the humoral immune response in vivo through classical vaccination and infection model. Furthermore, we use this model to perform in vitro differentiation assay to precisely determine at the cellular and molecular level the role of Sec22b in plasma cell fate. Tissues and cells in culture are investigated through classical techniques like multiparametric flow cytometry, ELISA or immunohistofluorescence but also through more cutting-edge approaches like single-cell microfluidics quantification of antibody secretion rate (DropMap), RNAseq or high resolution microscopy of the organelles structure.

Thanks to an original mouse model we were able to demonstrate that the SNARE molecule Sec22b is indispensable for plasma cell biology and the humoral immune response through several mechanisms:
We demonstrated that Sec22b is important for antibody trafficking from the endoplasmic reticulum to the Golgi.
We also reported that in absence of Sec22b, the endoplasmic reticulum fails to expand while mitochondria accumulate in plasma cells. In parallel, the unfolded protein response is exacerbated.
Altogether, these defective cellular processes contribute to the defective survival and expansion of mutant plasma cells.
As a consequence, in absence of Sec22b expression in the B cell lineage the vaccinal and infectious humoral response is totally impaired.

In the next coming months, we will decipher more precisely how Sec22b regulates the biogenesis of organelles and how these processes regulate the survival, proliferation and maturation of plasma cells.

Papers published and acknowledging the support of the ANR:
1. Leupaxin Expression Is Dispensable for B Cell Immune Responses. Bonaud A, Clare S, Bisio V, Sowerby JM, Yao S, Ostergaard H, Balabanian K, Smith KGC, Espéli M.Front Immunol. 2020 Mar 25;11:466. doi: 10.3389/fimmu.2020.00466
2. Hematologic disorder-associated Cxcr4 gain-of-function mutation leads to uncontrolled extrafollicular immune response. Alouche N, Bonaud A, Rondeau V, Hussein-Agha R, Nguyen J, Bisio V, Khamyath M, Crickx E, Setterblad N, Dulphy N, Mahevas M, McDermott DH, Murphy PM, Balabanian K, Espéli M.Blood. 2021 Jun 3;137(22):3050-3063. doi: 10.1182/blood.2020007450.
3. Hematopoietic Multipotent Progenitors and Plasma Cells: Neighbors or Roommates in the Mouse Bone Marrow Ecosystem? Bonaud A, Lemos JP, Espéli M, Balabanian K.Front Immunol. 2021 Apr 15;12:658535. doi: 10.3389/fimmu.2021.658535.
Book chapters published and acknowledging the support of the ANR:
1. Culture, Expansion and Differentiation of Human Bone Marrow Stromal Cells. Bisio V, Espéli M, Balabanian K, Anginot A.Methods Mol Biol. 2021;2308:3-20. doi: 10.1007/978-1-0716-1425-9_1.
2. Culture, Expansion and Differentiation of Mouse Bone-Derived Mesenchymal Stromal Cells. Abou Nader Z, Espéli M, Balabanian K, P Lemos J.Methods Mol Biol. 2021;2308:35-46. doi: 10.1007/978-1-0716-1425-9_3
3. Feeder-Free Differentiation Assay for Mouse Hematopoietic Stem and Progenitor Cells. Rondeau V, Espéli M, Balabanian K.Methods Mol Biol. 2021;2308:47-58. doi: 10.1007/978-1-0716-1425-9_4.
4. Immunophenotyping of the Medullary B Cell Compartment In Mouse Models. Bonaud A, Balabanian K, Espéli M.Methods Mol Biol. 2021;2308:95-105. doi: 10.1007/978-1-0716-1425-9_8.
Presentation at international scientific meetings on this specific topic:
1. 3rd French Germinal centre club workshop Virtual meeting 2021
2. EBC Net virtual meeting 2021
3. European Congress of Immunology 2021

Plasma cells and the antibodies they secrete are essential for long-term protective immune responses and tissue homeostasis. However, they can also contribute to the pathology of numerous inflammatory and autoimmune conditions. Despite their relevance in health and disease, the mechanisms underlying antibody production and secretion are still poorly understood. This is an essential question as a better characterization of the involved molecular actors may pave the way to improved antibody production, and to the development of new therapies for antibody-driven diseases. Preliminary data obtained in our laboratory showed that the Sec22b SNARE is essential for antibody secretion but also for plasma cell maturation. Using a conditional mouse model we observed in absence of Sec22b in the B cell lineage an almost complete lack of circulating antibodies and a dramatic decrease in the number of plasma cells in the spleen and the bone marrow. We now plan to use this model to address how Sec22b affects plasma cell fitness and antibody secretion. In parallel we will determine the impact of such defects on the normal and pathological humoral immune response and on tissue homeostasis, in particular in the BM. Collectively, this project should bring new lights on the molecular mechanisms underlying antibody secretion by plasma cells, a key process with huge relevance both at the therapeutic and at the industrial levels but largely overlooked so far. Moreover, our model will allow us to study with great details the impact of plasma cells and antibodies on homeostasis and inflammation at the tissue and organism level.