PhD Scientific Days 2022

Budapest, 6-7 July 2022

Molecular Sciences I. (Poster discussion will take place in the Aula during the Coffee Break)

Detailed Characterization of Developing Bursa of Fabricius Reveals a Novel Lymphoid Follicle Inducer Cell Type

Szőcs Emőke 1, Soós Ádám 1, Halasy Viktória 1, Jancsovics Dalma 1, Nagy Nándor 1

1 Semmelweis University, Department of Anatomy, Histology and Embriology, Budapest

Text of the abstract

Introduction: The avian bursa of Fabricius (BF) is a primary lymphoid organ, critical to normal B-lymphocyte development. During embryogenesis the epithelial anlage of the BF emerges as a diverticulum of the cloaca surrounded by undifferentiated mesenchyme. While it is believed that CD45+ hematopoietic stem cells colonize the epithelial-mesenchymal primordium that would provide a selective microenvironment for B cell precursor expansion, it is more likely that separate B-cell, macrophage, dendritic cell precursors colonize the mesenchyme, and some precursors migrate to the surface epithelium initiating lymphoid follicle bud formation.
Aims: The goal of this project is to characterize the developmental mechanisms of lymphoid follicle formation and to describe the ontogeny of the lympho-myeloid stem cells which colonize the bursal epithelium.
Methods: Early bursal development was characterized in wild type and CSF1R-eGFP transgenic avian embryos using a large panel of monoclonal antibodies (mAbs) specific for leukocytes (CD45), B-cells (chB6, EIVE12), macrophages (TIM4), bursal dendritic cells (CSF1R). Fate mapping of cell populations was performed by chorioallantoic membrane transplantation.
Results: The staining of embryonic BF helps to distinguish between three different lineages of hematopoietic cells. CD45+/EIVE12+ cells were first observed in the BF rudiment, many of them enter the surface epithelium to induce follicle bud formation. This will be colonized by the second cell type that belong to the CSF1R+/TIM4+ population, followed by chB6+ B cell precursors.
In conclusion, we could determine three different types of precursors which colonize the embryonic BF, indicating that there is a pre-bursal segregation between these blood-borne cell lineages. Using chick-duck chimeras, we demonstrate that the first cell types which enter the bursal epithelium are not the dendritic/macrophages or B cell precursors, but are a transient lymphoid bud inducer cell population whose primary role is to induce follicle bud formation.

Funding: NKFI - 138664
Semmelweis University, Doctoral School of Molecular Medicine
Supervisor: Dr. Nándor Nagy