What are the signals that induce heavy-chain isotype switching, and what is the importance of this phenomenon for host defense against different microbes? What is affinity maturation? How is it...

What are the signals that induce heavy-chain isotype switching, and what is the importance of this phenomenon for host defense against different microbes? What is affinity maturation? How is it induced, and how are high-affinity B cells selected to survive? What are the principal clinical manifestations of advanced HIV infection, and what is the pathogenesis of these manifestations?