Skin, immune cell, and serum Ig changes in MYD88^L265Pmice. (A) Representative gross pathology photographs of submandibular skin showing dermatitis and alopecia in MYD88^L265P but not MYD88^WT mice. (B) H&E, Giemsa, and IHC stains of indicated cell markers on serial submandibular skin sections from representative MYD88^WT and MYD88^L265P mice. Giemsa stain was used to identify mast cells; F4/80, macrophages. Scale bars: white, 10 µm; black, 100 µm. Percentage of T cells (C), macrophages (D), and mast cells (E) or number of mast cells relative to the tissue area (F) per field in the submandibular skin of MYD88^WT and MYD88^L265P mice. Measurements were made with inForm Cell Analysis Software analyzing 8 fields per genotype. Graphs depict the mean ± SD. P values were calculated by using Welch’s t test. (G) Histologic (H&E) analysis of representative cervical LNs demonstrating cyst development in MYD88^L265P but not in AID^Cre or MYD88^WT mice. Scale bars: white, 50 µm; black, 500 µm. Representative density plots (H) and graphs (I) depicting the mean ± SD of flow cytometric analysis of splenic lymphoid cell subpopulations from AID^Cre (n = 6), MYD88^WT (n = 7), and MYD88^L265P (n = 6) mice immunized with SRBCs. (J) Serum Ig concentrations assessed using multiplex immunoassay in MYD88^L265P mice grouped according to severity of submandibular skin lesions. Graphs depict the median ± 25th to 75th percentile. P values were calculated by using Mann-Whitney U test. (K) Percentage of MYD88^L265P mice classified by the severity of submandibular skin lesions with serum IL-6 concentrations >49 pg/mL assessed using multiplex immunoassay. P value was calculated by using Fisher’s exact test. (L) IHC stains of indicated cytokines on serial submandibular skin sections from representative MYD88^WT and MYD88^L265P mice. Scale bars: white, 10 µm; black, 100 µm.