The IFN-regulatory factors IRF1, IRF3, IRF5, and IRF7 modulate processes involved in the pathogenesis of systemic lupus and
lupus nephritis, but the contribution of IRF4, which has multiple roles in innate and adaptive immunity, is unknown. To determine a putative pathogenic role of IRF4 in lupus, we crossed Irf4-deficient mice with autoimmune C57BL/6-(Fas)lpr mice. IRF4 deficiency associated with increased activation of antigen-presenting cells in C57BL/6-(Fas)lpr mice, resulting in a massive increase in plasma levels of TNF and
IL-12p40, suggesting that IRF4 suppresses
cytokine release in these mice. Nevertheless, IRF4 deficiency completely protected these mice from
glomerulonephritis and
lung disease. The mice were hypogammaglobulinemic and lacked antinuclear and
anti-dsDNA autoantibodies, revealing the requirement of IRF4 for the maturation of plasma cells. As a consequence, Irf4-deficient C57BL/6-(Fas)lpr mice neither developed
immune complex disease nor glomerular activation of
complement. In addition, lack of IRF4 impaired the maturation of Th17 effector T cells and reduced plasma levels of
IL-17 and
IL-21, which are
cytokines known to contribute to autoimmune tissue injury. In summary, IRF4 deficiency enhances systemic
inflammation and the activation of antigen-presenting cells but also prevents the maturation of plasma cells and effector T cells. Because these adaptive immune effectors are essential for the evolution of
lupus nephritis, we conclude that IRF4 promotes the development of
lupus nephritis despite suppressing antigen-presenting cells.