Latent lymphokines: isolation of guinea pig latent lymphocyte-derived chemotactic factor for monocytes. Its activation by trypsin and a soluble factor from macrophages.

Guinea pig lymphocytes when depleted of macrophages and stimulated by the T cell mitogen phytohemagglutinin produce a latent form of lymphocyte-derived chemotactic factor for monocytes (LDCF-M). Latent LDCF-M is also produced when immune lymphocytes are stimulated in vitro with specific antigen, horseradish peroxidase. Latent LDCF-M from both sources can be activated and converted to "classical" LDCF-M by trypsin and by a soluble factor obtained from sonicated macrophages. These observations suggest that macrophages may modulate lymphokine activities in vivo by releasing soluble factors that convert inactive latent lymphokines to biologically active substances.