Using an ELISA specific for anti-IFN IgG antibodies to assess the pharmacokinetics of the anti-human IFN monoclonal antibody rontalizumab in SLE, Morimoto et al. observed anti-interferon antibodies (AIAAs) in 27% of rontalizumab–naïve patients, the majority of whom had significantly lower levels of serum type 1-IFN and downstream IFN pathway activity [10]. The gene discussed is IFNA1; the disease is systemic lupus erythematosus.