CD8A and Atrophy: Laboratory animal thymus atrophy via CD4+CD8+ lymphocyte apoptosis has been associated with any type of stress, such as restraint, irritation, trauma, or social stress, which is mediated by glucocorticoid release from the adrenal cortex (Warholm et al., 1984; Nakanishi et al., 1998; Dal-Zotto et al., 2003; Rodrigues-Mascarenhas et al., 2006).