Short-term administration of IL-7 does not affect thymic cytoarchitecture, but greatly affects spleen and lymph node cytoarchitecture. Hematoxylin and eosin-stained sections were prepared of thymus (cortex [C] and medulla [M]), spleen (arrows indicating arterioles within periarteriolar T-cell zones), and mesenteric lymph node (B-cell follicles [B] and T-cell parafollicular zones [T]). Mice treated with rmIL-7 (5 μg per day for 14 days) were compared with diluent controls. Magnification: ×100 in all sections. Sections shown here are representative of 6 mice in each group.