In humans delayed hypersensitivity to tuberculin and coccidiodin can be transferred from a skin-test positive donor to a previously nonreactive recipient with a dialyzable fraction of donor peripheral leukocytes. The mechanism by which transfer is effected by this relatively low molecular weight material is unknown. Should transfer with dialysate be accomplished with hypersensitivity to low molecular weight artificial antigens, further characterization of “transfer factor” might be facilitated.
