Abstract
In contrast to mammals, early B cell differentiation and diversification of the antibody repertoire in chickens do not take place in the bone marrow but in a specialized gut associated lymphoid tissue (GALT), the bursa of Fabricius. During embryonic development, B cell precursors migrate to the bursa anlage, where they proliferate and diversify their B cell receptor repertoire. Around hatch these diversified B cells start to emigrate from the bursa of Fabricius and populate peripheral lymphoid organs, but very little is known how the migratory processes are regulated. As CXCL12 (syn. SDF-1) and CXCR4 were shown to be essential for the control of B cell migration during the development of lymphoid tissues in mammals, we analyzed expression and function of this chemokine/chemokine-receptor pair in the chicken bursa. We found a strong variation of mRNA abundance of CXCL12 and CXCR4 in different stages of bursa development, with high abundance of CXCL12 mRNA in the bursa anlage at embryonic day 10 (ED10). In situ hybridization demonstrated disseminated CXCL12 expression in the early bursa anlage, which condensed in the developing follicles and was mainly restricted to the follicle cortex post-hatch. Flow cytometric analysis detected CXCR4 protein already on early B cell stages, increasing during bursal development. Post-hatch, a subpopulation with the hallmarks of emigrating B cells became detectable, which had lower CXCR4 expression, suggesting that downregulation of CXCR4 is necessary to leave the CXCL12-high bursal environment. In vivo blockade of CXCR4 using AMD3100 at the time of B cell precursor immigration strongly inhibited follicle development, demonstrating that CXCL12 attracts pre-bursal B cells into the bursal anlage. Altogether, we show that CXCL12 and its receptor CXCR4 are important for both populating the bursa with B cells and emigration of mature B cells into the periphery post hatch, and that CXCR4 function in primary B cell organs is conserved between mammals and birds.
Highlights
The widely accepted dogma is that development of B cells with a highly diversified receptor repertoire is a continuous lifelong process, which takes place in the bone marrow [1]
To examine if CXCL12 and CXCR4 play a role in chicken B cell development, we started with an analysis of CXCL12 and CXCR4 mRNA abundance in bursa samples from different developmental time points: embryonic day 10 (ED10) = immigration of prebursal B cells, ED18 = no immigration/no emigration/strong proliferation, D2 = emigration and proliferation, D28 = terminally differentiated tissue with follicles separated in cortex and medulla
Sort-purified B cells from ED18 and D2 were compared with total bursal tissue and, while CXCL12 mRNA was detected at much higher levels in bursal tissue than in B cells (500 fold at ED18 and more than 15,000 fold at D2), abundance of CXCR4 was relatively similar in B cells and total tissue (Figure 1B), which argues for CXCL12 expression by non-B-cells/stroma cells and a main expression of CXCR4 mRNA in B cells
Summary
The widely accepted dogma is that development of B cells with a highly diversified receptor repertoire is a continuous lifelong process, which takes place in the bone marrow [1]. This certainly is true for human and mouse, but many higher vertebrate species use a different strategy to diversify the B cell repertoire, which includes gut-associated lymphoid tissue (GALT) structures [2,3,4]. The bursal phase starts between embryonic day 9 (ED9) and ED12, when a small number of pre-bursal stem cells migrates to the bursa anlage, where each of 10,000–12,000 lymphoid follicles is colonized by only 2–5 B cell precursors [7]. Post-hatch, the formerly homogeneous bursa follicles compartmentalize into dense highly proliferating B-cells in a cortex and a more heterogeneous medulla with B-cells and several types of myeloid cells and stroma cells, including bursal secretory dendritic cells [13]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
