Question

he innate immune system was likened to ordinary police and the adaptive immune system was likened to spe- cialized backups, such as snipers. For those of you who follow true crime or mystery stories, you might find it amusing—and helpful in your studies—to try to come up with other criminal justice analogies. For example, you might make an analogy between ‘‘an- tibody production by B cells’’ and ‘‘smart bombs, sur- veillance, and tracking devices.’’ See what you can do with Th cells, cytokines, APCs, and NK cells.

2. Does the fact that sIgA does not activate comple- ment make it less effective in preventing infection than IgG? Hint: consider its location and function.

3. Explain how the structure of an antibody is de- signed to facilitate the function of the particular an- tibody, e.g., why an antibody has at least two active sites, why it has an Fc portion, and why it might be cross-linked as multimers. 72 Chapter 4

4. Why is a Th1 or Th2 cell needed to mediate APC- initiated antibody production? Why do the B cells not bind directly to the APCs?

Answer 1

1. Th cells are like the guns and cytokines are the bullets which can kill the enemy which is the antigen when present in our territory which is the APC cell while NK cells is the merciless elimination of the enemy

2.No it does not make IgA less effective, it was necessary because if significant amount of complements were activated at mucosae it could lead to inflammation and damage to the epithelium. Secretory IgA is not an efficient activator of complement. Thus, even though monocytes, macrophages, and mucosal epithelial cells all synthesize complement pro-enzymes, the bias toward secretory IgA production in the mucosae decreases the chance of activating the complement cascade and initiating damaging inflammation

3. An antibody has at least two active sites because an antigen can have many different epitopes to which paratope can bind. When two or more epitopes are identical, an antibody can form a stronger bond with the antigen than if only one of the antibody's sites is bound. Fc portion determines the effector function of the antibodies. it is cross linked tp form the visible precipitate

4. Th1 or Th2 cell cannot identify and bind antigen as it is , it can only bind to antigen when it is presented by MHC displayed by APC, the Th cells become activated and release cytokines which activates B cells to release antibodies. B cells are itself antigen presenting cells