Accidental involution of thymus (mouse, malaria infection)

Stain: Hematoxylin & eosin. Due to the infection with malarial parasites (Plasmodium berghei in mice) a steroid-related involution of the thymus is induced in mice within 14 days. A: normal thymus with cortex (2) and medulla (1). B: There is still a quite large remnant of the original thymus tissue after 2 weeks, however without the architectural boundaries between cortex and medulla. The circulating steroids e.g. cortisol increases in levels due to the infection, or stress and induce lysis of the cortical thymocytes. Background: Lethal malarial infections are known to depress immune responses to certain antigens. In the mouse, they reduce the antibody and splenic plaque-forming cell response to sheep red blood cells (SRBCs), render animals more susceptible to lymphomagenic viruses, and severe long term infections prolong xenogeneic skin graft survival time.