FLRT2 and systemic lupus erythematosus: With purified IgG from one SLE patient with high AECA activity (E10-19), two distinct clones were isolated and established, both of which were shown to have an identical gene, FLRT2. As we confirmed that E10-19 IgG bound specifically to cell-surface FLRT2 and FLRT2 was expressed on the cell surface of ECs, we concluded that FLRT2 is a novel cell-surface autoantigen as a target molecule for AECAs in SLE patients.