Systemic lupus erythematosus (SLE) is a prototype of human systemic autoimmune diseases. The pathogenesis behind the disease remains unclear. It is a chronic disease characterized by multisystem organ affection; with recurrent remissions and exacerbations. Therefore, detecting changes in disease activity is of great importance.A Proliferation Inducing Ligand (APRIL) is a novel member of the tumor necrosis factor (TNF) ligand superfamily. It was named for its capacity to stimulate tumor cell proliferation in vitro and provides survival and activation signals to normal B and T cells. Also now APRIL acts as a proliferative factor in megakaryocytopoiesis, there are growing evidences that APRIL contributes to the pathogenesis of SLE.Aim of the work:The aim of this work is to study the role of APRIL in SLE pathogenesis by detecting its mRNA expression in peripheral blood mononuclear cells (PBMCs) from SLE patients using conventional reverse-transcription polymerase chain reaction (RT-PCR) and correlate APRIL mRNA expression with different laboratory and clinical features of SLE.Results:Our study revealed statistically significant relation between APRIL gene expression and available clinical data of SLE patients with vasculitis, neurological symptoms and photosensitivity compared to controls.And no statistically significant relation between APRIL gene expression and available clinical data of SLE patients for arthritis, nephritis or disease activity index.