FAS and infection: Furthermore, the infection of chickens with IBDV increased the number of CD8+ T cells in the bursa and spleen, and the expression of Fas and Fas ligand (FasL), perforin (PFN), and granzyme-A (Gzm-A) in the bursa and spleen was significantly upregulated; this suggests that CTL may be involved in the clearance of IBDV from the target organ, the bursa, and peripheral tissues through both the Fas–FasL and perforin–granzyme pathways [93].