BTNL8 and systemic lupus erythematosus: Using rapid extracellular antigen profiling (REAP), Wang et al. discovered autoantibodies in SLE patients targeting 84 extracellular and secreted proteins, including cytokines (IL-6, INF-1, IL-1α, TNF-α), chemokines (CXCL3, CCL8, CCL22), growth factors (VEGF-B, FGF-21), and immunoregulatory proteins (CD44, CD95, PD-L2, butyrophilin-like 8 (BTNL8], B7-H4) [144].