PRF1 and ankylosing spondylitis: Nonbeneficial effects of anti-TNF immunotherapy in chronic inflammatory diseases (as rheumatoid arthritis and ankylosing spondylitis) associated with reactivation of Mycobacterium infection may be attributed to the depletion of the cytolytic CD8+perforin+/granulysin+ CTL population by Infliximab [19].