Lympho-proliferation and splenomegaly are more pronounced in mA3 deficient mice. Age and weight-matched WT, mA3+/-, and mA3-/- male mice on C57BL/6 background (n = 5) were inoculated with PBS (negative control) or LP-BM5 virus via the IP route (A). Eight weeks after inoculation, mice were sacrificed. Spleen sizes (B) and weights (C) were recorded for each genotype. Single cell suspension was obtained from splenocytes and stained with cell surface antibodies to differentiate B cells from CD4 + T lymphocytes and determine lymphocyte number using flow cytometry. B cell percentage was detected with anti-B220 (D and E), and CD4 + T percentage was detected with anti-CD4 (D and F). Activation of CD69 expression on B cells (G) and CD4+ T cells (H) was detected upon triple-staining with anti -B220, -CD4, and -CD69. Flow cytometry data were analyzed with Flowjo. Error bars are standard error; * is significance with p value equal or less than 0.05; and ** is significance with p value equal or less than 0.01. Experiments were repeated at least three different times with similar results and representative data presented.