1996a-999 2011b-305 activeoxygen adaptiveimmunity antioxidants bacteria congresses drugeffects freeradicals host-pathogeninteractions immuneresponse immunity immunologicaldeficiencysyndromes immunology infection infections metabolism naturalimmunity nutritionalaspects nutritionalphysiologicalphenomena oxygen parasites physiologicaleffect qv800a278a1988 qw541c7581995 qw541i3262011 qw700i421981 viruses