the humeral part is done by macromolecules outside the cells. these may be secreted antibodies, complement proteins, or certain antimicrobial peptides. their job is to attack bacteria (and other foreign substances) which are loose in the blood stream or other fluids. in older medicine, these fluids were called "humors". both the more primitive innate immune system, and the later acquired or adaptive immune system of vertebrates, have humoral components.