Interleukins in immunologic and allergic diseases.

Figure 1 depicts some of the potential interactions of the interleukins. Among the substances discussed here, only IL-2 has been used to any large degree in a clinical series. Other cytokines not discussed including some of the colony stimulating factors, tumor necrosis factor and the interferons have also been used in clinical trials. Undoubtedly as we learn more about interleukins IL-1 through IL-7, clinical applications will become apparent. For the allergist/immunologist there are two areas of greatest potential interest. The first of these is in treating immunodeficiency states. Preliminary studies of the use of IL-2 in patients with T cell dysfunction suggest that this substance may be useful in treating selective T cell disorders. IL-4, 5, and 6 all have some influence on B cell function. It is likely that in the near future one or more of these agents will be used clinically. It is also clear that the interleukins have the potential to influence basic mechanisms known to be important in allergic disease. IL-3 is the major factor influencing mast cell growth. IL-4 among other things, promotes B cells to switch to IgE synthesis as well as to induce Fc epsilon RII receptors on B cells. IL-5 is important in the differentiation and growth of eosinophils. Finally, IL-6 is the terminal differentiation factor that causes B cells to become plasma cells. The next few years should result in an even better understanding of the role of each of these interleukins. It is likely that such information will greatly expand the horizons for understanding the pathogenesis of many immunologically mediated diseases and will provide the basis for new modalities of treatment.