chapter_9 - Chapter 9 The Humoral Immune Response This...

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Chapter 9 The Humoral Immune Response Most antibody (B cell) responses need “help” “Help” comes from T cells (signal 2) Most help comes from T H 2 but T H 1 can also provide help There are also antibody responses that do not require T help (Thymus-independent or T-independent antibody responses) T help controls or partly controls B cell proliferation, class switching, initiation of somatic mutations and memory Antibodies protect extracellular spaces, blood and certain surfaces from microorganisms This chapter deals with ( i ) activation of B cells, ( ii ) distribution of antibodies and ( iii ) destruction of antigen as a result of being targeted by antibodies
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Activation by antigen binding and helper T cell interactions Activation is proliferation and differentiation Examples of the mechanisms used by antibodies to get rid of antigens (mechanisms can be Ig isotype- specific) Also induces inflammation
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B cell activation T-independent antibody response generally have 1. no memory 2. no isotype switching (IgM only) 3. no somatic mutations Thymus-dependent because T cells are required Thymus-independent because T cells are not needed Some responses require T help whereas other do not
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For us, signal 2 is provided to B cells by CD40L and and IL-4 (other cytokines involved, too) Recall, T cell activation up-regulates T cell expression of CD40L (and next slide) For B cells, “help” is Signal 2
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1 2 CD40 B7 MHC II TCR and CD28 on T cell bind MHC II plus peptide and B7 on dendritic cell CD40L binding to CD40 causes the dendritic cell to express high levels of B7 to better interact with T cells and activate them Secrete IL-2 T cell get signals 1 and 2 resulting in T cell expression of CD40L, high affinity IL-2 receptors and secretion of IL-2 CD40L CD40L
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T help for B cells is via the same antigen that is recognized by the B cell However, not necessarily by the same epitope Linked recognition Linked recognition
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Linked recognition Linked recognition T H T H Peptide 52-67 Peptide 34-48 (Specific for peptide 34-48) (Specific for peptide 52-67) Antigen processing Antigen presentation MHC class II = TH can recognize any of these peptides and provide “help” B cell antibody is specific for peptide 68-74
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Figure 9.4 B cell and T helper cells recognize epitopes of the same molecular complex but not necessarily the same epitopes. Linked recognition
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If T cells recognize only peptides, how do you make antibodies to polysaccharides or other non-protein macromolecules? For a thymus- dependent antibody responses, protein must be part of the antigen Thymus dependent antigens (TD antigens) Linked recognition = protein = polysaccharide Haemophlius influenzae type B vaccine
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IL-4 is secreted in the direction of the B cell so there is little bystander effect on neighboring B cells Fig. 8.29 Recall the cytotoxic T lymphocyte killing mechanism
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Those B cells and T cells that bind antigen are trapped in the T cell zone of the peripheral lymphoid organ where they can both get activated and interact Recall T cell circulation from Chapter 8
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This note was uploaded on 09/22/2011 for the course BIOL 6570 taught by Professor Jenniferleavey during the Spring '11 term at Georgia Tech.

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chapter_9 - Chapter 9 The Humoral Immune Response This...

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