Chapter 12: B Cell Activation and Antibody Production What is humoral immunity? It is the component of the immune system that uses antibodies produced by differentiated B cells (plasma cells) to provide us with protection against pathogens. As we will see, antibodies can be secreted or membrane bound, but humoral immunity specifically refers to using secreted antibodies. Overview of B cell activation: Let’s start at the beginning…How do antigens get to the B cells? Abbas, Lichtman and Pillai8_Figure 12-1; p.240 Abbas, Lichtman and Pillai8_Figure 12-4; p.243B cell activation T-dependent vs. T-independent antigens Abbas, Lichtman and Pillai8_Figure 12-3; p.242 Abbas, Lichtman and Pillai8_Figure 12-5; p.244Now that antigens have activated the B cells, what do B cells do next? T-dependent B cells are a little complicated… Abbas, Lichtman and Pillai8_Figure 12-6; p.245 Abbas, Lichtman and Pillai8_Figure 12-7; p.246How do T cells find the B cells they are specific to (share the same antigen recognition)? The hapten-carrier effect Abbas, Lichtman and Pillai8_Figure 12-8; p.246B cell activation using helper T cells (aka. Helper T cell-mediated B cell activation. Abbas, Lichtman and Pillai8_Figure 12-10; p.248 Abbas, Lichtman and Pillai8_Figure 12-11; p.250Isotype Switching Abbas, Lichtman and Pillai8_Figure 12-12; p.251 Abbas, Lichtman and Pillai8_Figure 12-14; p.252Of great importance to keep in mind is that when we change the isotype of the antibody, we do NOT change the antigen to which it can recognize – we are only changing the function that antibody has against that particular antigen. So, how does isotype switching occur? Abbas, Lichtman and Pillai8_Figure 12-15; p.253Affinity Maturation Antibody Testing Abbas, Lichtman and Pillai8_Figure 12-17 (on right) and Figure 12-18 (on left); p.255 Abbas, Lichtman and Pillai8_Figure 12-19; p.256How to make antibody-secreting plasma cells B cell responses to T-independent antigens are far more simplified than to T-dependent antigens (but, also not as good!) Thymus-Dependent Antigen Thymus-Independent Antigen Chemical nature Proteins Polymeric antigens, especially polysaccharides; also glycolipids, nucleic acids Features of Antibody Response Isotype switching Yes; IgG, IgE, and IgA Little or no; may be some IgG and IgA Affinity maturation Yes No Secondary response (memory B cells) Yes Only seen with some antigens (e.g., polysaccharides) Abbas, Lichtman and Pillai8_Figure 12-20; p.258 Table 12-2: Properties of Thymus-Dependent and Thymus-Independent Antigens; p.259Why are memory cells so important? Abbas, Lichtman and Pillai8_Figure 12-2; p.241Stopping the B cell response is just as important as initiating it… Abbas, Lichtman and Pillai8_Figure 12-21B;
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