Why is a Th1 or Th2 cell needed to mediate APCinitiated antibody production? Why do the B cells not bind directly to the APCs? Explain why direct antigen activation of CTLs and B cells is more...

Why is a Th1 or Th2 cell needed to mediate APCinitiated antibody production? Why do the B cells not bind directly to the APCs?

Explain why direct antigen activation of CTLs and B cells is more important than APC-initiated activation in subsequent encounters with a microbe. Why is the APC-initiated pathway needed at all?