STAT3 and Splenomegaly: Considering the reduction in splenomegaly with these results, the absence of STAT3 in B cells of stat3f/f;CD19Cre/+ mice reduced the total number of viral genome-positive splenocytes by 36-fold, from approximately 286,000 cells in the control mice to 7,910 cells in the stat3f/f;CD19Cre/+ mice (Table 1).