( 2 ) mos t component s of th e immunologi c syste m i n huma n mil k ar e produce d throughou t lactation an d durin g gradua l weaning ; ( 3 ) th e factor s ar e usuall y commo n to othe r mucosa l sites ; ( 4 ) the y ar e adapte d t o resis t digestio n i n th e gastrointestinal trac t of th e recipien t infant ; ( 5 ) they protec t b y noninflammatory mechanisms ; an d ( 6 ) th e agent s ac t synergisticall y wit h eac h othe r or with defense agent s produced b y the recipient.