IL15 and rheumatoid arthritis: RA synovium is enriched with bone marrow cells (monocytes, macrophages, neutrophils, eosinophils, basophils, red blood cells, dendritic cells, and megakaryocytes or platelets) and plasma-like dendritic cells, which produce various cytokines (IL-12, IL-15, IL-18, IL-6, IL-32), HLA class II molecules, and co-stimulatory molecules responsible for T-cell activation and presentation 34.