In this video, we're going to begin our introduction to T lymphocytes or T cells. First, we need to recall from some of our previous lesson videos that T lymphocytes or T cells play an important role in cell-mediated immunity, which is a part of adaptive immunity. Cell-mediated immunity targets and destroys intracellular pathogens, or disease-causing agents that have made their way inside of a host cell. It does this by using, once again, T cells or T lymphocytes. We are going to continue to introduce and talk about T cells and T lymphocytes as we move forward. What you'll notice here is that we're showing you the primary lymphoid organs here, and recall that T cells are developed in the thymus. After these T cells are fully developed, the naive forms of the T cells or the inactive forms of the T cells will migrate to the secondary lymphoid organs, like tonsils, lymph nodes, or the spleen.
Really, what we're going to learn moving forward is that there are two major types of T cells. There are cytotoxic T cells or TC cells, and there are also helper T cells or TH cells. As we move forward in our course, we will differentiate between these two types of T cells. Both the cytotoxic T cell and the helper T cell need to be activated by an antigen-presenting cell such as a dendritic cell. Here, we show a dendritic cell presenting antigens on its surface so that they can activate these T cells. Upon activation of the T cells, these T cells will begin to divide and differentiate into either memory T cells—notice that there are both memory cytotoxic T cells, memory TC cells, but there are also memory TH cells as well or memory helper T cells. In addition to generating these memory cells, they also differentiate into effector cells as well, effector helper T cells, and also effector cytotoxic T cells.
What you'll notice is that it's these effector T cells that can go on to carry out the immune functions. The memory T cells are stored for generating an immune response to a secondary infection, a potential secondary infection. Notice that the B cells are being shown over here on the right-hand side, but we're going to talk about the B cells later in our course after we finish talking about the T cells. Everything that we've discussed here in this video about the T cells will be broken down and explained in more details as we move forward. This concludes our brief introduction to T lymphocytes. We'll continue learning about them as we go forward. So, I'll see you all in our next video.