In this video, we're going to briefly discuss the IgM class of antibody. The IgM antibody is very important for controlling infections in the blood. It is actually the very first antibody that is going to be initially produced in a primary infection by plasma cells before a process known as class switching takes place. Later in our course, in a different video, we'll talk more about this antibody class switching. The IgM class of antibody is also the largest class of antibody in terms of its size and molecular mass because IgM antibodies consist of a pentamer, which means that it is composed of 5 identical Y-shaped subunits. Because it has 5 Y-shaped subunits, each subunit with 2 antigen binding sites, that means that there are 10 antigen binding sites. Because there are so many antigen binding sites on these IgM antibodies, that makes them very effective at linking antigens together. The large size of the IgM antibody class actually prevents the IgM antibody from leaving the blood, into the tissues. Thus, the primary role of the IgM antibody is to help control infections in the blood. Also, the IgM class of antibody is the most efficient antibody class at activating the complement system via the classical pathway.
If we take a look at our image down below, we'll have an image that helps to emphasize these same features of the IgM class of antibody. Notice first that it is indeed a pentamer that consists of these five identical Y-shaped subunits. That makes it the largest antibody class in size. Also, it is the very first antibody that is initially created by all plasma cells prior to the antibody class switching process that we'll get to talk about in more detail later in our course. The primary role of the IgM antibody, because of its large size, is to control infections in the bloodstream. This is the most effective antibody at activating the complement system. It activates the complement system when it binds to the antigen. Here we have a little image that shows you C3 convertase being generated upon activation of the complement system and then all of these actions that result from the complement system activation, including inflammation, opsonization, and cell lysis of microbes. If you don't remember much about the complement system, make sure to go back to our older lesson videos to check them out. This concludes our brief lesson on the IgM class of antibody, and we'll be able to get some practice applying these concepts and talk about the other classes as we move forward. So, I'll see you all in our next video.