Many SLE patients show a distinctive "interferon signature" — a pattern of elevated expression of interferon-stimulated genes detectable in blood — that correlates with disease severity and appears to identify a specific biological subtype of the disease. This has directly enabled precision medicine in SLE: anifrolumab, which blocks the type I interferon receptor, shows its strongest treatment effects in patients with a high interferon signature at baseline. As interferon-signature testing becomes more accessible, it may allow clinicians to select interferon-targeted therapies (anifrolumab, and investigational agents like litifilimab) specifically for the subset of patients most likely to benefit, rather than treating all SLE patients as a single uniform population.