Mice transgenic for BAFF (B cell activating factor belonging to the TNF family) develop autoimmune-like disorders, including high levels of rheumatoid factors, circulating immune complexes, anti-DNA autoantibodies, and immunoglobulin deposition in the kidneys. These mice exhibit increased numbers of mature B and effector T cells, along with signs of B cell activation and T cell alterations. BAFF, a TNF family member, binds to B cells and promotes their growth. Transgenic mice overexpressing BAFF under a liver-specific promoter show expanded B cell compartments, increased Ig levels, and autoimmune manifestations. The study highlights the role of BAFF in B cell regulation and its potential involvement in autoimmune diseases. BAFF overexpression leads to the expansion of B cells, increased Ig production, and autoimmune-like symptoms, suggesting that dysregulation of BAFF expression may contribute to autoimmunity. The findings provide insights into the mechanisms underlying autoimmune disorders and suggest that BAFF could be a target for therapeutic interventions.Mice transgenic for BAFF (B cell activating factor belonging to the TNF family) develop autoimmune-like disorders, including high levels of rheumatoid factors, circulating immune complexes, anti-DNA autoantibodies, and immunoglobulin deposition in the kidneys. These mice exhibit increased numbers of mature B and effector T cells, along with signs of B cell activation and T cell alterations. BAFF, a TNF family member, binds to B cells and promotes their growth. Transgenic mice overexpressing BAFF under a liver-specific promoter show expanded B cell compartments, increased Ig levels, and autoimmune manifestations. The study highlights the role of BAFF in B cell regulation and its potential involvement in autoimmune diseases. BAFF overexpression leads to the expansion of B cells, increased Ig production, and autoimmune-like symptoms, suggesting that dysregulation of BAFF expression may contribute to autoimmunity. The findings provide insights into the mechanisms underlying autoimmune disorders and suggest that BAFF could be a target for therapeutic interventions.