BCL2L1 and rheumatoid arthritis: Additionally, its role in other immune cells (and recruited from other locations, e.g., tissue/synovium) needs to be further elucidated as there is scientific evidence that increased expression of MCL-1 in synovial fibroblasts and synovial macrophages or an increased expression of BCL-XL in osteoclasts contributed to disease progression in RA [27–29].