Isolation and characterization of lymphocyte mitogenic factor released in vivo during a cell-mediated immune reaction in the guinea pig.

By use of a guinea pig model of delayed hypersensitivity to horseradish peroxidase (HRPO), it has been possible to characterize the rate of release of lymphocyte mitogenic factor (MF) in vivo after i.p. challenge immune animals with antigen. MF is present in peritoneal fluid of immune guinea pigs 4 to 12 hr after i.p. challenge with HRPO, before 2 other lymphokines, lymphocyte-derived chemotactic factor for monocytes and macrophage migration-inhibitory factor, are released. The m.w. of MF generated in vivo and in vitro, as estimated by gel filtration, are similar, approximately 25,000. In vivo and in vitro MF are stable upon heating to 56 degrees C for 30 min. This observation that a mitogenic factor for lymphocytes is released early in vivo in a delayed hypersensitivity reaction gives support to the notion that its primary function in vivo may be to amplify cell-mediated immune reactions.