Autoantibody production in B6.GT mice. (A) Spontaneous autoimmune skin lesions and ear pinna erosion in old B6.GT mice. (B) IgM and IgG anti–double-stranded DNA-specific autoantibodies in serum from 5 age-matched female B6.WT, B6.TRAIL^−/−, B6.gld/gld, and B6.GT mice. Shown are endpoint titers of individual mouse sera (●) and mean autoantibody levels (horizontal line) of 5 mice per strain. (C) IgM and IgG rheumatoid factor antibodies: anti–rabbit Ig, or anti–mouse IgG2a antibodies, determined by standard ELISA, on serum from 5 age-matched female B6.WT, B6.TRAIL^−/−, B6.gld/gld, and B6.GT mice. Endpoint titers (●) and mean autoantibody levels are shown (horizontal line). (D) FACS analysis of B6.WT platelet-bound IgG and IgM autoantibodies in K₂EDTA-anticoagulated serum obtained from old B6.WT (n = 5), B6.TRAIL^−/− (n = 5), B6.gld/gld (n = 10 shown of 15 analyzed), or B6.GT mice (n = 10 shown of 15 analyzed). Serum antiplatelet antibody capacity to block detection of CD41 and CD61 is also shown. Log scale SSC/FWD scatter platelet events were gated to exclude 99.9% of electronic noise. (E) Visualization of megakaryocytes in Wright Giemsa-stained bone marrow smears. Scale bar represents 50 μm. (F) Enumeration of CD41^hiCD61^hi bone marrow megakaryocytes per 100 000 bone marrow leukocytes as determined by flow cytometry. Data are individual bone marrow megakaryocytes per pair mouse femurs (●), and means of bone marrow megakaryocytes from 5 mice per strain (horizontal line), calculated from CD41 versus CD61 dot plots of FWD-area large cells (< 0.5% events), pregated for singlet cells determined from FWD-height versus FWD-area dot plots (supplemental Figure 3). No statistically significant differences were found between any strains by 1-way analysis of variance.