278 paRT I Immune Effector mechanisms get Cell Effect Activatio Activated Tu cells PLEIOTROPY IL-4 Proliferation IFN-Y Thymocyte Activated TH cells Mast cel REDUNDANCY 9→出彐 Proliferation 12 Activated Tu cells B cell SYNERGY IL-4 Induces class switch to lge IL-5 Activated TH cells ANTAGONISM Activated TH cells IL-4 Blocks class switch to IgE induced by IL-4 IFN-Y IFN-Y TNF, IL-2, and Activated Tu cells B cell other cytokines FIGURE 12.2 Cytokine attributes of (a)pleiotropy, redundancy. synergy(synergism), antagonism, and(b) cascade induction immune-system cells. Soon after, it was discovered that pro- natans and the absence of well-defined assay systems for duction of these factors by cultured lymphocytes was induced individual cytokines. a great advance was made with the by activation with antigen or with nonspecific mitogens. Bio- development of gene-cloning techniques during the 1970s chemical isolation and purification of cytokines was ham- and 1980s, which made it possible to produce pure cytokines red because of their low concentration in culture super- by expressing the protein from cloned genes. The discovery ofimmune-system cells. Soon after, it was discovered that pro￾duction of these factors by cultured lymphocytes was induced by activation with antigen or with nonspecific mitogens. Bio￾chemical isolation and purification of cytokines was ham￾pered because of their low concentration in culture super￾natants and the absence of well-defined assay systems for individual cytokines. A great advance was made with the development of gene-cloning techniques during the 1970s and 1980s, which made it possible to produce pure cytokines by expressing the protein from cloned genes. The discovery of 278 PART III Immune Effector Mechanisms Activated TH cells PLEIOTROPY Mast cell IL-4 Thymocyte B cell Activation Proliferation Differentiation Proliferation Target Cell Effect IL-4 Proliferation IL-2 IL-5 Activated TH cells REDUNDANCY IL-4 + IL-5 Activated TH cells SYNERGY Induces class switch to IgE Blocks class switch to IgE induced by IL-4 IL-4 IFN-γ Activated TH cells ANTAGONISM Proliferation B cell B cell B cell Activated TH cells Activated TH cells IFN-γ, TNF, IL-2, and other cytokines Macrophage IL-12 CASCADE INDUCTION IFN-γ (a) (b) FIGURE 12-2 Cytokine attributes of (a) pleiotropy, redundancy, synergy (synergism), antagonism, and (b) cascade induction