This video, we're going to talk about another way that some viruses can evade the immune system, and that is by avoiding the effects of antibodies. Similarly to bacteria, viruses can also rapidly change their surface structures due to mutations that accumulate in their genome during replication. These mutations that accumulate in the viral genome can change its surface structures, and those changes in the surface structures allow the virus to once again evade the adaptive immune response, specifically evading the antibodies. Some viruses use antibodies to enhance their infection by the process of antibody-dependent enhancement, also known as ADE for short. Viral particles that are bound by antibodies in this process of ADE are engulfed by macrophages where the virus is actually able to actively replicate.

If we take a look at our image down below over here on the left-hand side, we're showing you how some viruses are able to mutate to avoid antibodies. Notice over here on the left-hand side we're showing you our normal virus and this virus is going to have viral surface proteins. What you'll notice is that the viral surface proteins over here on the left-hand side are pink and circular. Through mutations that can accumulate as this virus replicates, these mutations can lead to changes in the surface molecules of the virus. Now, this virus has new viral surface proteins, and the surface proteins have gone from pink circles to being these blue squares. Thus, the antibodies that used to be effective towards the circular pink viral proteins are no longer effective towards the bluish square surface proteins. By mutating, the virus is able to evade the effects of the antibodies.

Now over here on the right-hand side, we're also showing you how viruses can actually use antibodies themselves to enter cells in the process of antibody-dependent enhancement or ADE. In this image, you'll notice that there is a virus, and the virus is being bound by these antibodies. But these antibodies are actually going to assist with the virus's replication. These antibodies will actually enhance the ability for this virus to replicate. Notice that the virus is saying "Engulf me, I dare you" to the macrophage. As these antibodies are bound, it leads to phagocytosis. However, this virus is able to evade destruction and it is actually able to replicate inside of the macrophage via this process. The virus replicates within the macrophage, evading the antibodies and evading the immune system. This here concludes our brief lesson on how some viruses are able to avoid the effects of antibodies in order to evade the immune response. We'll be able to get some practice applying this as we move forward. So I'll see you all in our next video.