Development of DLBCL in MYD88^L265Pmice. (A) Gross pathology images of spleens (top, in situ; bottom, dissected) and LNs from MYD88^L265P mice with DLBCL. Scale bars, 1 cm. (B) Histologic and IHC stains of indicated markers on serial LN (top) and kidney metastasis (met.) (bottom) sections from MYD88^L265P mice (n = 2) with DLBCL. Note punctate cytoplasmic MYD88 staining in the lymphoma cells (white arrowheads). Scale bars: white, 20 µm; black, 100 µm; yellow, 5 µm. (C) Density plots of flow cytometric analysis of indicated lymphocyte subpopulations in LNs from representative, age-matched AID^Cre control and MYD88^L265P DLBCL mice. (D) Clonality evaluated by Southern blot analysis of the IgH gene in DNA isolated from LNs, spleen (Sp), liver (Li), and tumor (T) of MYD88^L265P (n = 3) mice with DLBCL. Clonal rearranged bands are indicated with white arrowheads. (E) Location of murine MYD88^L265P and corresponding human DLBCL⁶  somatic mutations in affected proteins.