Progression of histologic lesions within the mesenteric lymph nodes of mice infected with "scid-adapted" MARV. Scid mice were challenged intraperitoneally with 1000 plaque-forming units of 'scid-adapted' MARV-Ci67 and tissue samples were collected on days 0, 2, 4, 6, and 8 after challenge (n = 4–5/group). (A-F) Tissues from the MARV-infected mice were stained with hematoxylin and eosin and representative pictures from day 0 (A), day 2 (B), day 4 (C), and days 6 and 8 (D, E, F) are shown. (A) Control scid mouse sampled at day 0 (i.e. uninfected) contain abnormal lymph node morphology due to a paucity of B and T lymphocytes and failure of follicle development. (B) No significant histologic changes compared to uninfected lymph nodes observed at day 0. (C) By day 4, mesenteric lymph nodes from the MARV-infected scid mice exhibited minimal to mild lymphoid depletion and a slight increase in the number of tingible body macrophages. (D, E) At days 6 and 8, lymphoid depletion and lymphocytolysis was a consistent finding in the mesenteric lymph nodes of all MARV-infected scid mice. (F) At day 8, note the increased numbers of tingible body macrophages containing variably sized apoptotic-like bodies. Magnifications were 10× for panels A, B, C, D, and E and 40× for panel F. Tingible body macrophages are indicated by arrow heads.