280 PART III Immune Effector Mechanisms VISUALIZING CONCEPTS immunity Cytokine promotion of activation, differentiation, proliferation, or cell death of T cells, B cells, macrophages. dendritic cells, NK cells, and other leukocytes. FIGURE12.5 Interaction of antigen with macrophages and the merous cytokines(blue arrows), generating a complex network of ubsequent activation of resting TH cells leads to release of nu- interacting cells in the immune response share a similar polypeptide fold, with four a-helical regions and differentiation, and the healing of wounds. Although the (A-D)in which the first and second helices and the third and immune response to a specific antigen may include the pro- fourth helices run roughly parallel to one another and are duction of cytokines, it is important to remember that connected by loops. cytokines act in an antigen-nonspecific manner. That is, they affect whatever cells they encounter that bear appropriate Cytokines Have Numerous Biological receptors and are in a physiological state that allows them Functions to respo Cytokines are involved in a staggeringly broad array of Although a variety of cells can secrete cytokines, the two biological activities including innate immunity, adaptive principal producers are the TH cell and the macrophage. immunity, inflammation, and hematopoiesis. Altogether, the Cytokines released from these two cell types activate an total number of proteins with cytokine activity easily exceeds entire network of interacting cells(Figure 12-5). Among the 100 and research continues to uncover new ones. Table 12-1 numerous physiologic responses that require cytokine in- summarizes the activities of some cytokines and places them volvement are development of cellular and humoral im- into functional groups. An expanded list of cytokines can be mune responses, induction of the inflammatory response, found in the Appendix. It should be kept in mind that most regulation of hematopoiesis, control of cellular proliferation of the listed functions have been identified from analysis ofshare a similar polypeptide fold, with four -helical regions (A–D) in which the first and second helices and the third and fourth helices run roughly parallel to one another and are connected by loops. Cytokines Have Numerous Biological Functions Although a variety of cells can secrete cytokines, the two principal producers are the TH cell and the macrophage. Cytokines released from these two cell types activate an entire network of interacting cells (Figure 12-5). Among the numerous physiologic responses that require cytokine in￾volvement are development of cellular and humoral im￾mune responses, induction of the inflammatory response, regulation of hematopoiesis, control of cellular proliferation and differentiation, and the healing of wounds. Although the immune response to a specific antigen may include the pro￾duction of cytokines, it is important to remember that cytokines act in an antigen-nonspecific manner. That is, they affect whatever cells they encounter that bear appropriate receptors and are in a physiological state that allows them to respond. Cytokines are involved in a staggeringly broad array of biological activities including innate immunity, adaptive immunity, inflammation, and hematopoiesis. Altogether, the total number of proteins with cytokine activity easily exceeds 100 and research continues to uncover new ones. Table 12-1 summarizes the activities of some cytokines and places them into functional groups. An expanded list of cytokines can be found in the Appendix. It should be kept in mind that most of the listed functions have been identified from analysis of 280 PART III Immune Effector Mechanisms VISUALIZING CONCEPTS Inflammation Macrophage Resting TH cell Adaptive immunity Cytokine promotion of macrophage activation Cytokine promotion of TH cell differentiation Hemato￾poiesis Cytokine promotion of activation, differentiation, proliferation, or cell death of T cells, B cells, macrophages, dendritic cells, NK cells, and other leukocytes. FIGURE 12-5 Interaction of antigen with macrophages and the subsequent activation of resting TH cells leads to release of nu￾merous cytokines (blue arrows), generating a complex network of interacting cells in the immune response.