Apoptosis within the spleen and liver of 'scid-adapted' MARV-infected mice. Sections of the spleen and liver from mice infected with 'scid-adapted' MARV-Ci67 were stained using a TUNEL assay. (A-B) Control scid mouse sampled at day 0 (i.e. uninfected) contain TUNEL-positive cells, indicated by brown staining, in the spleen (A) and liver (B) due to natural turnover of naïve 'break-through' lymphocytes. (C-D) Increased number of TUNEL-positive cells in the spleen (C) and liver (D) of MARV-infected scid mice at day 6 postinfection.