The role of cell-mediated immunity in the induction of inflammatory responses. Parke-Davis Award Lecture, 1977.

Reactions of cell-mediated immunity fall into two broad categories: those that involve direct participation of intact lymphocytes in the effector mechanism of the reaction and those that involve mediation by soluble lymphocyte-derived factors known as lymphokines. The first kind of reaction is essentially limited to lymphocyte-dependent cytotoxicity, although certain aspects of T cell-B cell cooperation may fall into this category as well. The second category appears to comprise the bulk of the so-called cell-mediated immune response and provides a link between this system and the inflammatory system. Various lymphokines have been shown to exert profound influence upon inflammatory cell metabolism, cell surface properties, patterns of cell migration, and the activation of cells for various biologic activities involved in host defense. Although substantial information is now available about various physicochemical as well as biologic properties of lymphokines, purification and characterization data are as yet too incomplete to allow us to ascribe all of these activities to discrete mediator molecules. Current work involving the development of antibody-based techniques for mediator assay may shed light on this issue. Information on the kinds of cells capable of lymphokine production is now available. Contrary to prior expectation, T cells are not unique in their capacity for lymphokine production. Under appropriate circumstances, B cells and even nonlymphoid cells can do so as well. The unique property of lymphocytes in this regard appears to relate to their ability to respond to certain specialized signals such as specific antigen or an appropriate mitogen. Mediator production per se may represent a general biologic phenomenon. Although lymphokines have been defined mainly in terms of in vitro assays, early speculations about their in vivo importance are proving correct. Evidence for the role of lymphokines comes from studies involving detection of lymphokines in tissues, studies involving injection of exogenous lymphokines, and studies involving suppression of in vivo reactions by various techniques. The use of antilymphokine antibodies has proven useful in the latter kinds of experiments. Work in many laboratories is beginning to relate these findings to clinically relevant situations. A major unsolved problem relates to the regulation and control of lymphokine production and activity. At present only a limited body of information is available on this point. This is a potentially fruitful area for future investigation since it may provide techniques for manipulating the immune system in ways that are clinically useful.