Dysregulation of the granulocyte-macrophage colony-stimulating factor receptor is one of the causes of defective expression of CD80 antigen in systemic lupus erythematosus.

CD80 and CD86, expressed on the antigen-presenting cells (APCs) provide costimulatory signals for T lymphocytes. Recently, defective expression of CD80 has been reported in systemic lupus erythematosus (SLE) although its mechanism is unclear. Here, expression of the B7 antigens induced by interferon-gamma, interleukin-4 or granulocyte-macrophage stimulating-factor (GM-CSF) along the differentiation process of APCs was investigated. In contrast to CD86, expression of CD80 on the CD14+ cells induced by GM-CSF was reduced in SLE. GM-CSF receptor (GM-CSFR) was down-regulated by GM-CSF or phorbol 12-myristate 13-acetate in both of the normal controls and SLE patients, while this change was more remarkable in the latter. In the presence of 1-(5-isoquinolinsulfonyl)-2-methylpiperazine, an inhibitor of protein kinase C, the PMA-induced down-regulation of GM-CSFR was reversed in the normal controls but not in SLE. These data suggest that dysregulation of the GM-CSFR might be associated with the defective expression of CD80, leading to dysfunction of the APCs in SLE.