Based on my immunology knowledge, naïve B and T cells don't life very long. If an antigen comes along and they activate, you get a memory cell that sticks around and gives you longer lasting immunity. However, what about later on down the road for things we haven't seen? For T cells: T cells are made from hematopoietic stem cells from bone marrow but mature in the thymus. I was told that the thymus pretty much stops producing new naïve T cells sometime in our 20s. Now if this is true, that means in our late 20s/early 30s we would have no naïve T cells left. How is it then, that people of this age can have immunity to something they have never encountered. No memory cells and no naïve cells floating around.
Were my professors wrong and naïve cells stick around for a long time? If not, whats the explanation? How do we have immunity at this age?
TL;DR I think we stop producing naïve T cells in our 20s. How can we have immunity to novel infections at this age without naïve cells?
Considering a naïve B cell specific for a thymus-dependent antigen (i.e. a peptide), what differences will it face when being activated for the first time vs contacting the same antigen as a memory B cell?
Will the B cell need help from a Th lymphocyte in both cases? If that is so, is the interaction between CD40 and CD40L the only difference you can find between the two mechanisms of activation?
The Tea Party and Republicans let Mitt Romney be the 2012 candidate. Not a great guy, but probably better than Bush and didn't send his supporters to threaten to kill Joe Biden and Speaker Boehner. McCain 2008, defends a Black Democrat against a racist woman calling him an Arab, instead of joking along and saying "I get you, I wonder if he really was born here." Trump 2016, a total charlatan and sketchy corrupt guy, questioned elections, etc, but few members of Congress were calling to kill each other. But by the end of Trump, we've ended up with a party that is going to start a civil war at this rate and seems to want to end democracy as soon as possible.
How did this happen? By 2030 we'll be living in a military state or at best Putin's Russia.
