Histologic analysis of target tissues from mice segregating the splenomegaly phenotype. Spleen (S) (R indicates red pulp; W, white pulp), bone marrow (BM) and lymph nodes (LN) from (BALB/cJ × BXH-2)F2 mice showing presence (high SI) or absence (low SI) of splenomegaly were harvested, fixed, sectioned, and stained with hematoxylin and eosin. Original magnification was × 40 (M,O), × 400 (A,C,E,G,I,K), and × 1000 (B,D,F,H,J,L,N,P). Important infiltration of cells with neutrophil-like appearance with “ring” nuclei is seen in red pulp of the spleen, bone marrow, and in enlarged lymph nodes of F2 mice showing splenomegaly.