UBC Theses and Dissertations
Early embryonic surgical bursectomy : an investigation of some aspects of the avian immune system Sparks, Esta Madeleine Frances
Surgical removal of presumptive bursal tissue at 72 hr in ovo results in high mortality before hatching and low survival in the first week thereafter. The viable chicks are underweight and usually remain so. Both the spleen and thymus of the bursectomized (Bx) chicks are reduced in size and lymphoid population. The effect on the thymus may be related to stress and subsequent adrenal cortical activity or may reflect some endocrine function of the bursa necessary for the maturation of thymic lymphoid tissue. The effect on the spleen seems to be more direct. In the absence of the primary level organ which induces maturation of the stem cells, the number of germinal centres in the secondary level organ is reduced. Some of the remaining germinal centres may be of T-cell origin, although these cells are more commonly found in diffuse lymphoid areas. The bulk of the germinal centres found in the Bx spleen must be of B-cell origin. Repeated stimulation of the humoral immune system with antigens and mitogens elicits a response in some Bx birds. The response is generally not found in the primary stimulation and is rarely of the magnitude of a normal response even after several stimulations. Antibody production may be limited to IgM type immunoglobulin; further studies are necessary to verify this. Autopsy and histological examination of the tissues of the responsive birds failed to show any evidence of residual bursal tissue. Whether these findings constitute proof of the role of the bursa in the humoral immune response or whether they reflect the broader consequences of bursectomy in the development of the bird requires further study. The inductive capacities of the bursa and the source and autonomous capacity of the stem cells thought to be induced in the bursa should also be investigated. The effects of early hormonal and late surgical bursectomy are similar to those found in this study, where an early embryonic surgical technique was used to avoid the possible complications of these other methods.
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