Answer: antigens

AnswerCrossword Clue
ANTIGENSForeign instigators?
ANTIGENSThey induce immune system responses
antigensany substance (as an immunogen or a hapten) foreign to the body that evokes an immune response either alone or after forming a complex with a larger molecule (as a protein) and that is capable of binding with a product (as an antibody or T cell) of the immune response
antigensANTIGEN, a substance that stimulates the production of antibodies, also ANTIGENE