In this video, we're going to talk more details about opsonization, which is one of the three effects of complement system activation. Opsonization is really just a process that makes microbes easier to bind and engulf during the process of phagocytosis, which recall is cellular eating. During the process of opsonization, microbes are going to be coated with these molecules called opsonins. Opsonins are really just these small molecules that will bind to the cell surface of microbes, and they can be recognized by cell surface receptors of phagocytic cells. For example, C₃B is an opsonin, it will bind to the surface of microbes. By binding to the surface of microbes, C₃B can make phagocytosis much easier and more effective for phagocytic cells.

If we take a look at our image down below, notice at the top we're showing you a map of our lesson that starts with C₃ convertase. We know that activation of the complement system through either of the three pathways will ultimately lead to C₃ convertase, which will ultimately lead to one of these three effects of the complement system activation. In this video, we're focused on opsonization. On the left-hand side, we're showing you a little cartoon. If there is no opsonization, then notice that the macrophage, which is our phagocytic cell, is going to have a lot more trouble phagocytosing the microbe. Notice here the microbe is saying "can't catch me," and the macrophage is asking "why can't I grab you?" Phagocytosis is much more difficult if there is no opsonization.

Through opsonization, these opsonin molecules, which are these little blue circles, will bind to the surface of the microbes. Those little opsonins somewhat act as little grips that makes it a lot easier for the phagocyte to bind and phagocytose the microbe. Notice that these gloves here are representing opsonin cell surface receptors that allow for the phagocyte to bind a lot easier to the microbe. Notice that the macrophage is saying, "gotcha now." And the microbe here is not very happy saying, "oh, no." Basically, what we're saying here is that opsonization makes phagocytosis way easier for the phagocyte.

Up here at the top right, we're showing you a similar image, but we've got our macrophage here in blue, and it is phagocytosing this microbe that you see right here. If we zoom in, what you'll notice is that the microbe is going to be covered with C₃B, which is an example of an opsonin. The opsonin C₃B binds to the surface of the microbe, and so the cell surface receptors of the phagocyte can bind to the C₃B, and it makes it a lot easier for the phagocyte to phagocytose the microbe. Ultimately, what we're saying here is that opsonization is a process that makes phagocytosis much easier, more effective, and efficient.

This here concludes our brief lesson on opsonization, and we'll be able to get some practice applying these concepts as well as move forward and talk about the other effects of complement system activation including microbe sole lysis and the inflammatory response. So I'll see you all in our next video.