Fig 1: MDV inhibits cell proliferation in the bursa from 6 to 14 dpi but not in the thymus. A Proliferating cells were detected on both thymus (a–f) and bursa (g–l) of CTL and MDV-infected chicks at 6, 10 and 14 dpi by immunochemistry. For that, paraffin embedded sections were stained with a rabbit anti-cell nuclear antigen antibody (PCNA) revealed with EnVision anti-rabbit HRP kit after 3'diaminobenzidine (DAB) treatment (brown nuclei, as shown enlarged (×4) in the corner panel (a). The tissues were counterstained with Gill’s hematoxylin and the PCNA-negative nuclei appeared in blue. In the thymus, the number of PCNA-positive cells appeared to be equivalent in both groups of chicks. In the bursa, the total number of PCNA-positive cells was highly reduced in the infected group compared to the control group. PCNA-positive cells were mostly present in the bursal cortex of the control group. Bar, 50 µm. B Percentage of PCNA-positive cells in the bursa and the thymus at 6, 10 and 14 dpi. The median is represented with a black line. A significant reduction in the number of PCNA-positive cells was observed at each time point in the bursa, and not in the thymus