PDCD1 and helminthiasis: In subjects with chronic helminth infections and evidence of mycobacterial infection, in vitro studies have revealed diminished Th1 and Th17 responses to mycobacterial antigens [22–24]; these diminished responses are related to overexpression of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1), and transforming growth factor beta (TGF-β) and to exaggerated Th2 responses [25].