A Journey into the Bursa of Fabricius
Exploring T cell subsets through flow cytometry and their implications for poultry health
In the intricate landscape of the avian immune system, one organ stands out for its peculiarity and importance: the bursa of Fabricius. This unique structure, found only in birds, has fascinated scientists since its initial description by Hieronymus Fabricius in 1621 1 . For centuries, its function remained mysterious, but modern science has revealed it as the birthplace of antibody-producing B cells—so crucial that the "B" in B lymphocytes literally stands for "bursa-derived" 1 4 .
Flow cytometry allows researchers to identify and count specific immune cell types with remarkable precision, revealing unexpected T cell populations in the bursa.
The bursa of Fabricius serves as the primary site for B cell development in birds, making it essential for understanding avian immunity.
This chicken-specific organ located near the cloaca serves as a primary lymphoid organ, essential for the development and maturation of the immune system 1 .
Rapid growth during late embryogenesis and early life
Reaches peak relative size
Gradual regression after sexual maturation
While the bursa is famous for B cells, T cells represent another crucial arm of the adaptive immune system in chickens, responsible for cell-mediated immunity 5 .
Flow cytometry is a powerful laser-based technology that allows scientists to analyze the physical and chemical characteristics of cells or particles as they flow in a fluid stream through a beam of light. Think of it as an extremely sophisticated cell scanner that can rapidly process thousands of cells per second 3 .
Processes thousands of cells per second with precision
One significant hurdle in chicken immunology has been the low cross-reactivity of mammalian reagents with chicken cells due to limited homology at the molecular level between species 3 . However, the scientific community has made tremendous strides in developing chicken-specific antibodies.
Pan-T cell marker
Helper T cells
Cytotoxic T cells
Activation marker
A groundbreaking study published in 2024 provided unprecedented insights into how T cell populations in chicken lymphoid organs change during early development 5 .
Spleens collected at ED18, D5, and D30
Single-cell suspensions created through mechanical disruption
Cultured with Con A and chIL-2 for 5 days
Two antibody panels used for immune cell identification
Quantified percentages of T cell subsets
| Developmental Stage | CD4+ T Cells | CD8+ T Cells |
|---|---|---|
| Embryonic Day 18 | Lower | Lower |
| 5 Days Post-hatch | Increasing | Increasing |
| 30 Days Post-hatch | Higher | Higher |
| Cell Type | Percentage | Function |
|---|---|---|
| B Cells (Bu1+) | Highest | Antibody production |
| CD4+ T Cells | Significant | Immune regulation |
| CD8+ T Cells | Significant | Cell killing |
| Monocytes/Macrophages | Decreased | Phagocytosis |
The data demonstrated a clear expansion of both CD4+ and CD8+ T cell populations after hatching, with a particularly notable increase in activated T cells as the chickens matured 5 . This pattern suggests that the immune system becomes increasingly competent during the early post-hatching period.
| Reagent | Target/Function | Research Application |
|---|---|---|
| Anti-chicken CD3 | Pan-T cell marker | Identifies all T cells in samples |
| Anti-chicken CD4 | Helper T cell subset | Distinguishes CD4+ "helper" T cells |
| Anti-chicken CD8α | Cytotoxic T cell subset | Identifies CD8+ "killer" T cells |
| Anti-chicken CD44 | T cell activation marker | Detects recently activated T cells |
| Anti-chicken TCRγδ | Gamma-delta T cell subset | Identifies specialized T cell population |
| Anti-chicken CD45 | Pan-leukocyte marker | Distinguishes all white blood cells |
| Concanavalin A (Con A) | T cell mitogen | Stimulates T cell proliferation in culture |
| Chicken IL-2 | T cell growth factor | Supports T cell survival and expansion |
Understanding how T cell populations develop provides crucial insights for combating infectious diseases that threaten poultry flocks. For instance, infectious bursal disease virus (IBDV) specifically attacks the bursa of Fabricius 1 .
Fayoumi chicken lines show greater resistance to infections compared to Leghorn lines 2 .
As global demand for poultry products grows, maintaining flock health through improved immunity becomes increasingly important for sustainable food production.
The ex vivo bursal cell culture model supports Replacement, Reduction, and Refinement in animal research by providing an alternative to live animal studies while generating valuable immunological data .
The application of flow cytometry to study T cells in the bursa of Fabricius represents more than just a technical achievement—it symbolizes a new era in avian immunology where we can visualize and understand the intricate workings of the chicken immune system with unprecedented clarity.
As we unravel the mysteries of T cells in the bursa of Fabricius, we move closer to harnessing the full potential of the avian immune system—advancing both scientific knowledge and the practical goal of healthier, more resilient poultry flocks for a food-secure future.