BTK and rheumatoid arthritis: Some of the important proteins involved in RA include JAK, p38 mitogen-activated protein kinase (MAPK), extracellular receptor kinase (ERK), JNK, IL-1 receptor-associated kinase (IRAK)-4, MMPs, toll-like receptor 4 (TLR-4), G protein-coupled receptor kinase (GRK)-2, Bruton's tyrosine kinase (BTK), CD3, CD11a, CD19, CD20, and CD80.