CD28 and rheumatoid arthritis: ANA is an IL-1 receptor antagonist (IL-1ra), which blocks IL-1, involved in inflammation; a protein associated with joint destruction for RA.[45] ABA was composited of the extracellular domain and Fc portion of cytotoxic T lymphocyte-associated protein 4 (CTLA-4), which works by binding to the differential (CD)80/86 cluster on antigen-presenting cells (APC) and blocking the B7:CD28 interaction, then inhibiting joint inflammation.[46]