Th1 or Th2 lymphocyts

[Philippe AURIOL]

hello everybody, I'd like to ask you some immunological questions...

1/Does anybody know about the way a Th0 lymphocyts become a Th1 (IL2,
INFgamma) or a Th2 (IL3/4/6/8/10..)?

2/Some people say that it is the way  the allergies come, because of a
nearly orientation of Th2 lymphocyt, what do you think of that?

3/and then what is the time for a memory lymphocyt (CD45R0) to remain
active, in other word what is his during live?

Please answer me if you've got some informations about these three
questions.