The immunological specificity of a macrophage inhibition factor.

A system is described by which antigen-free supernatants can be obtained from cultures of specifically sensitized lymph node cells and antigen. By its use it has been possible to demonstrate that antigen (PPD or β-lactoglobulin) is needed for the inhibition of normal macrophage migration by cell free supernatants from the lymph node cultures. It, therefore, seems likely that the macrophage inhibition factor (MIF) detected in this system was not a non-specific macrophage glue' but an antibody-like' factor immobilizing normal macrophages in the presence of antigen.