The adaptive immune system is made of cells that can defend against specific pathogens, and the stars of the show are the T cells and the B cells. These are types of lymphocytes, which are cells found in lymph, that clear fluid of the lymphatic system, and they also include natural killer cells, which you might recall are part of the innate immune system. So, T cells, as we'll see, are going to be involved in what's called the cell-mediated response, be involved in the humoral response, and their job is going to be to produce antibodies and secrete them into the humors of the body. It's an old-fashioned term for the blood and the lymph, you know, the fluids of the body. They're going to produce antibodies and secrete them throughout the body, which will help recruit immune cells and also fight the pathogens directly.
Lymphocytes are going to be produced in bone marrow, like all leukocytes, and T cells and B cells are actually going to mature in different places. T cells are going to move to the thymus to mature, which is an organ, kind of like underneath the neck a little bit. You can see it right there in that picture and B cells will actually stick around in the bone marrow to mature. So, you can kind of remember it, you know, by T for thymus and B for bone marrow.
Lymphocytes are named because they are the main type of cell found in the lymph, and they circulate throughout the blood, lymphatic system, and the spleen, which is an organ that essentially filters the blood. It removes any damaged, dead, or compromised red blood cells, and these lymphocytes will also hang out in lymph nodes, which filter lymph, so they're basically going to be hanging around all the places that, you know, fluids of the body circulate through, and that's going to give them a really good access to any pathogens that have found their way into the body. There's a high probability that they'll run across them in these areas.
And here you can see a layout of the lymphatic system, the lymph vessels connecting all the little lymph nodes as well as the organs like the spleen and the thymus. And here you have an image of a lymph node. Jump out of the way here. And you can see that if you zoom in, you can see lymphocytes floating around in there, and, of course, this lymph node is going to have a lot of lymph vessels flowing into it, having their lymph filtered, and then the lymph will flow out of the node and continue flowing through the lymphatic system, and some fluid will actually re-enter the bloodstream.
Now, there's also this tissue type called mucosal-associated lymphoid tissue, or MALT, and basically, these are immune system cells that are going to be found in the gut and the respiratory tract. These tissues are going to be mucusy to scoop up any invading pathogens, and, you know, they are not labeled here in this image, but I want to bring your attention to them because they are part of this immune system and play an important role in picking up any pathogens.
Now, with that, let's flip the page.