VMC 221: Veterinary Immunology and Serology (1+1)

BURSA OF FABRICIUS

• Bursa of Fabricius is found only in birds and equivalent organs in mammals are gut associated lymphoid tissues (GALT) in Peyer’s patches of small intestine, lymphoid tissue of colon and appendix or tonsil.
• Bursa is a round sac like structure (elongated in case of ducks) originates from the dorsal epithelium diverticulum of the cloaca (located just above the cloaca).
• The bursa reached its maximum size by 3 weeks after hatch and then undergoes gradual involution.

Structure 

• Bursa consists of lymphocytes embedded in epithelial tissue. This epithelial tissue lines a hollow sac connected to the cloaca by a duct.
• Inside the sac, folds of epithelium (plicae) extend into the lumen. Each plica contains many lymphoid follicles (bursal follicle).
• Bursal follicles contain follicle associated epithelial cells, lymphocytes, macrophages and plasma cells
• Each follicle is divided into a cortex and medulla. The cortex is the outer part packed with lymphocytes, plasma cells and macrophages.
• The inner part is medulla. These stem cells under the influence of bursal micro environment (hormonal influence of bursepoietin/ bursin ) mature and differentiate into bursal lymphocytes or B cells.
• B cells appear in the bursa between12-15 days of embryonic development.
• Bursa is not a pure primary lymphoid organ because it can trap antigen and some antibody synthesis takes place. It also contains a small focus of T cells just above the bursal duct opening.

Bursal follicles

Function

• Differentiation of immature B- cells into immunocompetent B- cells (antibody producing cells)
• It can also trap antigen and produce antibody.