Lymphokine regulation of macrophage effector activities

Our concept of the regulation of macrophage activation is ever expanding and contracting. In regard to the number of LK that regulate macrophages killing activities, we have entered a new phase. In the beginning there was one macrophage activation factor, MIF; then there were many macrophage activation factors, most uncharacterized and bearing a variety of names. Then came IFN, a genetically cloned single reagent that induced destruction of virtually every target assessed; all activities of macrophages were assumed to be regulated by IFN. Once again, however, the LK universe is expanding: the number of single, cloned reagents that induce macrophage killing activities is amazing. With just two targets, a fibrosarcoma cell and an intracellular amastigote of L. major, we can identify 5 different macrophage activation factors, four of which are cloned and sequenced. As more recombinant reagents become available, the story of macrophage activation is likely to become even more complex. It is fascinating not only that certain of the LK are capable of inducing single effector reactions in the absence of effects on other effector activities, but also that at least one effector reaction requires the cooperation of several molecularly distinct LK. The complexity of LK activation factors that regulate a single effector reaction in vitro is compounded by the complexity in effector cell populations. For example, inflammatory macrophages exposed to LK kill the fibrosarcoma tumor target 5 to 10-fold better than an equal number of resident peritoneal macrophages. In contrast, LK treated resident macrophages eliminate intracellular amastigotes of leishmania far more efficiently than inflammatory cells. Thus, changes in cell populations dramatically affect the capacity to demonstrate a single effector reaction. Further, simple changes in assay conditions also determine whether an effector reaction can be observed in vitro. And superimposed upon all these layers of complexity is the target itself. The mechanisms a macrophages uses to block the replication of a virus may be totally ineffective in the destruction of a multicellular helminth, such as Schistosoma mansoni. And there is no reason to suspect that the extracellular destruction of a tumor target occurs by the same means that the macrophage uses to kill an intracytoplasmic bacterium, such as a rickettsia.(ABSTRACT TRUNCATED AT 400 WORDS)