PhD Scientific Days 2022

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

Characterization and Development of the Lymphoid Follicular Cortex of the Bursa of Fabricius

Text of the abstract

Introduction
The bursa of Fabricius (BF) is a primary lymphoid organ, unique in birds, that is responsible for the development of B cells within its follicular microenvironment. The bursal lymphoid follicles consist of two histologically and embryological distinct compartments: the ectodermal medulla and the cortex of mesodermal origin.
Aims
Despite the fact that the histology of the follicular medulla is well characterized, the morphology of the ontogenetically later emerging cortex is less clear.
Our aims are:
• Histological characterization of the follicular cortex with the help of immunohistochemistry and electronmicroscopy
• Detailed characterization of the cortical extracellular matrix proteins
• Ontogeny of the follicular cortex
Methods
Embedding, immunohistochemistry, embryomanipulation techniques, chorioallantoic membrane transplantation, in vitro cell cultures, RCAS-shh virus usage, confocal/STED/electronmicroscopy and statistical analysis were used in these experiments.
Results
In this study, we describe the molecular composition and ontogeny of the BF follicular cortex. In contrast to medulla, the adult cortical CD45+/chB6+
B-lymphocytes express surface CXCR4. In the cortex the reticular cells produce extracellular matrix (ECM) rich in proteoglycans, collagens, and glycoproteins, unlike the medulla where there is no detectable ECM. Characterization of the ECM showed that compared to most of the ECM proteins, expression of Tenascin-C can be first observed on 16th day of embryogenesis surrounding the developing follicle buds. Tenascin-C blocked B-cell migration in the explant cultures of embryonic BF. Similarly, RCAS-Shh retroviral vector-induced overexpression of Tenascin-C inhibits B-cell colonization of developing follicles.
Conclusion
1) development of the follicle cortex starts before hatching; 2) the B-cells of the cortical follicle shows a specific Bu-1+/CXCR4+/IgM low expression pattern, and has a CSF1R+/TIM4+/Lep100+ macrophage population; 3) the scaffold of the cortex is composed of mesenchymal reticulum cells that produce ECM; 4) In vivo and in vitro experiments show that Tenascin-C provides an inhibitory environment for B-cell migration.
Funding
Grant: NKFI - 138664