Effector forms of T cells are helper T cells 帮助 T 细胞 and cytotoxic T cells 毒性 T 细胞 • Helper T cells help activate B cells and cytotoxic T cells 帮助 T 细胞会激活 B 细胞和毒性 T 细 胞 • Cytotoxic T cells secrete proteins that lead to cell death in infected cells 毒性 T 细胞分泌蛋 白质，引起受感染的细胞死亡 Structure/Function Evolution Systems Information Flow Energy/Matter
Figure 43.16 Antigen- presenting cell Pathogen Antigen fragment MHC molecule Antigen receptor Helper T cell Cytokines B cell Cytotoxic T cell Cytokines from helper T cells help activate B cells and cytotoxic T cells Structure/Function Evolution Systems Information Flow Energy/Matter
Figure 43.17-3 Cytotoxic T cell 3 1 2 MHC molecule Infected cell Antigen receptor Antigen fragment Perforin Pore Gran- zymes Released cytotoxic T cell Dying infected cell Cytotoxic T cells bind to infected cells and secrete perforin and granzymes • Perforin causes pores to form in the cell membrane of infected cells • Granzymes initiate apoptosis 细胞凋亡
Memory cells are responsible for long- term protection provided by a prior infection or vaccination 记忆细胞形成 长期保护 • Memory cells, produced during the original B cell or T cell proliferation, give rise to effector cells if the same epitope is encountered again – Secondary immune response = rapid Structure/Function Evolution Systems Information Flow Energy/Matter
Figure 43.15 Primary immune response to antigen A produces antibodies to A. Secondary immune response to antigen A produces antibodies to A; primary immune response to antigen B produces antibodies to B. Exposure to antigen A Exposure to antigens A and B Time (days) Antibody concentration (arbitrary units) 10 4 10 3 10 2 10 1 10 0 0 7 14 21 28 35 42 49 56 Antibodies to A Antibodies to B
Figure 43.2 Pathogens (such as bacteria, fungi, and viruses) INNATE IMMUNITY (all animals) • Rapid response Recognition of traits shared by broad ranges of pathogens, using a small set of receptors • Recognition of traits specific to particular pathogens, using a vast array of receptors • • Slower response Barrier defenses: Skin Mucous membranes Secretions Internal defenses: Phagocytic cells Natural killer cells Antimicrobial proteins Inflammatory response Humoral response: Antibodies defend against infection in body fluids. Cell-mediated response: Cytotoxic cells defend against infection in body cells . ADAPTIVE IMMUNITY (vertebrates only)
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