In this video, we're going to begin our introduction to lymphocytes. Taking a look at our map of the lesson down below, we have natural killer cells, T cells, and B cells. Notice that these lymphocytes are all derived from common lymphoid progenitor cells. The T cells and B cells are the only lymphocytes listed here that are part of adaptive immunity. However, the natural killer cells, although they are lymphocytes, are not part of adaptive immunity but are part of innate immunity. Notice here that we're saying these lymphocytes include leukocytes that are important for adaptive immunity. But really, we're focusing specifically on the T cells and B cells when talking about lymphocytes important for adaptive immunity.

Adaptive immunity is a topic that we'll talk a lot more about later in our course, and it will be covered in other videos. The two major groups of lymphocytes that are important in adaptive immunity are once again the T cells and B cells. These cells respond to very specific antigens of invading microbes, and this specificity is a characteristic of adaptive immunity. Not all lymphocytes are part of adaptive immunity. It's important to note that there is a group of lymphocytes, specifically the innate lymphoid cells (ILCs), that differ from the B and T cells. The B and T cells are part of adaptive immunity, but the innate lymphoid cells are part of innate immunity. The innate lymphoid cells are commonly abbreviated as ILCs, and they differ from the B and T cells due to a lack of specificity in antigen recognition. While T cells and B cells are very specific and part of adaptive immunity, the innate lymphoid cells lack specificity.

A classic example of ILCs, or innate lymphoid cells, are the natural killer cells, abbreviated as NK cells. These natural killer cells are innate lymphoid cells, and they kill a variety of different cell types, so they are not specific to one type of antigen. They are non-specific. Taking a look at this image over here, notice that we're focusing specifically on the lymphocytes. The lymphocytes include natural killer cells, which are innate lymphoid cells that are part of innate immunity, but it also includes the T cells and B cells, which are important for adaptive immunity and adaptive immune responses.

We'll be able to talk in much more detail about the T cells and B cells later in our course when discussing adaptive immune responses. We will also talk more about the lymphocytes at that time, including more details about the natural killer cells in those separate videos. For now, this concludes our brief introduction to lymphocytes, and we'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.