Helper T cells are the other type of effector T cells and their role is to assist with the activation of other immune cells and to recruit other immune cells by secreting cytokines. There are actually two types. There are Th1 cells whose specific role is to activate those cytotoxic T cells, and there are Th2 cells whose specific role is to help activate B cells which we'll talk about in just a moment. I just want to quickly point out this diagram of a helper T cell which, if it encounters the appropriate MHC, or appropriate antigen bound to the MHC protein, it's going to respond by either activating B cells, macrophages, or T cells or releasing cytokines to attract other immune cells. That's what's going on in this image.
Now, B cell activation occurs when a B cell receptor interacts with a free-floating antigen that has an epitope it can bind to and it will find these in the lymph or in the blood. Now, that antigen, when it's bound to the B cell receptor, will be ingested into the cell, then digested, and then part of it will be attached to an MHC class 2 protein and transported to the cell surface where it will be displayed. Now, Th2 cells that have complementary receptors to the displayed antigen will bind to the B cells and this Th2 cell will be activated by that interaction with the B cell and it will cause it to release cytokines and those cytokines will then, in turn, stimulate that B cell. So they'll basically have an interaction where they stimulate each other. They complement each other and stimulate each other and this causes the B cell to become fully activated and when it's fully activated, it's going to replicate and generate effector and memory cells. So, that's what's going to, you know, cause the B cell to, you know, produce those clonal populations and in that process, those B cells will experience what's called somatic hypermutation. Essentially, it's just like lots of mutation but kind of like planned for mutation. I don't want to say controlled mutation but it's like the cells induce this mutation and it allows those replicating B cells to actually fine-tune the receptor to bind the antigen better.
Now, these fully activated B cells are going to, as I said, produce effector and memory cells. The effector cells, or some of the effector cells it will produce are called plasma cells. These are effector B cells that produce massive amounts of antibodies and secrete those antibodies into the blood. B cell encounters, the appropriate B cell encounters, the appropriate antigen, you see this B cell can't bind that antigen, so it's not going to be activated and, then the B cell has an interaction with the helper T cell which causes it to become the basic idea behind how these B cells are going to do their job. With that, let's flip the page.
