ISG15 and systemic lupus erythematosus: Our study shows that in SLE patients with LN, full vaccination against SARS-CoV-2 did not consistently augment neutralizing antibody titers but was accompanied by an increase in type I and III interferon activity and selected pro-inflammatory cytokines, together with upregulation of the ISG15 gene-encoding protein induced by type I IFN in T cells.