CD52 and rheumatoid arthritis: Secondary HLH is associated with infections (viral, fungal, bacterial, and parasitic), drugs (methotrexate, non-hormonal anti-inflammatories, anticonvulsants, anti-TNF-α, anti-CD52), autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, Sjögren syndrome, systemic sclerosis, and Kawasaki disease), neoplasms (lymphomas), and immunosuppression (solid organ transplantation).1,2,5,9,10,12,13,14,16 A diagnostic criteria was proposed in 1991 and revised in 2004 by the International Society of Histiocytosis and includes 8 items of which at least 5 must be present (Chart 1).1,2,6,8