Thymic development in surgically bursectomized embryonic chicken: expression of PCNA, CD3, CD4 and CD8 markers

Little information is available on the functional relationship between bursa and thymus during chicken embryogenesis. We, therefore, investigated embryonic thymuses taken at 17 days in ovo from chickens bursectomized at 68-72 hours, with histological, histochemical (PAS, Alcian blue), and immunoreaction (anti-cytokeratin B, anti-PCNA/cyclin and anti-CD3, CD4 and CD8 antibodies) methods and compared these data with those from normal and sham-operated chickens of the same age. The bursectomized thymuses distinctly differed from normal and sham-operated thymuses: they were smaller, and the cortical zone was thinner and contained fewer epithelial cells and thymocytes. Only few cortical thymocytes were immunoreactive for PCNA, indicating low proliferative rate. More cortical thymocytes as compared with the normal, expressed CD3 on their cell membrane, whereas the thymocytes at the cortical-medullary border expressing anti- CD4 and anti-CD8 antidodies were less numerous than in normal thymus. The medullary zone contained few epithelial clusters made up of fewer cells than medullary clusters in normal chickens. Some cystic formations were enlarged and contained PAS- or Alcian-blue positive amorphous material. All these data suggest that early bursectomy affects both morphological and functional thymic development.