00:01
Hey everybody, so this question is asking us about b cell activation and how b lymphocytes go from being unactivated precursor cells that are simply in the circulation to being triggered by an antigen in the body and turning into plasma cells.
00:24
So they're now activated cells.
00:25
They're taking part in our adaptive immune response.
00:28
Once they are activated.
00:30
So they turn from b lymphocytes into b plasma cells.
00:36
And in part a of this question, it specifies that b cells have to be bound by multivalent antigens in order to be activated.
00:52
So they have to be bound by multivalent antigens in order to be activated.
00:57
And so that's going to give us, and then asks us, well, what does this mean about the activation of b cells? what can we say about the mechanism of activation of b cells? so i'm going to diagram out of b cell here.
01:13
Here's the cell surface.
01:17
It's a b lymphocyte, b lymphocyte.
01:27
And embedded in the cell surface of the cell all over are going to be b cell receptors.
01:35
So b cell receptors.
01:44
And if we were to have one small little antigen bind to one of these receptors, it wouldn't really do much for activating the b cell.
01:53
There would be no signal transduction through the membrane and into the b cell to tell it to turn into a plasma cell.
02:00
It would simply kind of keep going on as it had been from the very beginning.
02:06
However, if we were to take away this and go, on have a larger antigen presented say a bacterial cell so a bacterial cell on its own is going to be pretty large right and all of our b cell receptors are binding here to this bacterial cell on all these different spots this is going to go ahead and activate our b lymphocyte and so that gives us a couple of different hints as to why this is like how b cells actually become activated first of all, it is kind of a safety mechanism to make sure that our lymphocytes aren't activated too easily, right? we don't want to have an accidental activation of our b lymphocyte, and so we want to make sure that multiple of our b cell receptors are being bound, and that's only going to happen if we find this big, large antigen that has multiple binding sites for the b lymphocyte.
03:15
And so that's going to ensure that whenever it's activated, it's actually responding to a real pathogen.
03:22
It's not being activated by mistake.
03:25
Another hint that this is going to give us about how b cells are activated is that when this antigen is present on the outside of the cell, it's going to actually cluster these b cell receptors together in the plasma membrane...