Defining biological subsets in systemic lupus erythematosus: progress toward personalized therapy.

Systemic lupus erythematosus (SLE) is a heterogeneous disease with respect to disease severity, response to treatment, and organ damage. The pathogenesis of SLE includes immunological mechanisms which are driven by both genetic and environmental factors. There are clear differences in the pathogenesis of SLE between patients of different ancestral backgrounds, including differences in genetic risk factors, immunological parameters, and clinical manifestations. Patients with high vs. low levels of type I interferon (IFN) in circulation represents one major biological subset within SLE, and these two groups of patients are present in all ancestral backgrounds. Genetic factors, autoantibodies, and levels of other cytokines all differ between high and low IFN patients. This distinction has also been important in predicting response to treatment with anti-type I IFN therapies, providing a precedent in SLE for biological subsets predicting treatment response. This review will highlight some recent developments in defining biological subsets of SLE based on disease pathophysiology, and the idea that improved knowledge of disease heterogeneity will inform our efforts to personalize therapy in this disease.