3) Surviving Inside Phagocytic Cells - Online Tutor, Practice Problems & Exam Prep

Surviving Inside Phagocytic Cells

In this video, we're going to talk about yet another method that some pathogens can use to evade or avoid the immune system, and that is through surviving inside of phagocytic cells. So recall from some of our previous lesson videos that we describe the process of phagocytosis in a stepwise manner. And so recall from those videos that when a pathogen is engulfed by a phagocyte, that pathogen will enter the phagocyte within a phagosome. And the phagosome will generally fuse with a lysosome, which will allow for the pathogen to be digested and eliminated. Now some bacteria have evolved mechanisms to be able to survive inside of a phagocytic cell even after they have been engulfed. And they can do this in 3 different ways that we have down below in our image. And so notice in this image on the outside right here what we have is our pathogen. And of course, our phagocytic cell is going to be this big blue cell that you see here. This is going to be our macrophage. And so notice that the pathogen, here has opsonins on its surface and those opsonins allow for the process of opsonization that makes the pathogen easier to be engulfed through the process of phagocytosis. And so when the pathogen is engulfed, notice that it is brought into the cell, within a phagosome. Okay? Now the first mechanism that some bacteria have evolved to survive inside of phagocytes is, they have evolved mechanisms to escape from the phagosome before the phagosome fuses with the lysosome. And so what you'll notice here in this image, right here in this region, we are showing you how some bacteria have evolved the mechanism to escape the phagosome. And when they escape the phagosome, they escape their destiny to be degraded and destroyed. And so when they escape, they are able to survive within the macrophage. Now another mechanism that some bacteria have been able to evolve over time to survive in phagocytes is that they can avoid or block the fusion of the phagosome with the lysosome by producing inhibitory proteins. And so notice here that, sometimes right here, step number 2, where the phagosome would usually fuse with lysosomes, this step can be blocked and prevented. And so that will allow the pathogen to survive within the phagosome and not have to worry about the digestive enzymes from the lysosome. Now the third possibility here that some bacteria have evolved is the amazing ability to be able to survive inside of the phagolysosome even after the lysosomes have fused with the phagosome. And so, even when the lysosomes fuse with the phagosome and all of these digestive hydrolytic enzymes are there, trying to degrade the pathogen. In some cases, the pathogens have been able to survive those conditions and avoid being destroyed by the contents of the lysosome. And so notice this pathogen here is saying 'can't kill me' because they are able to survive even inside microbes that are able to survive inside of phagocytes by using each of these 3 different methods. And so this here concludes our brief lesson on how some pathogens can survive inside of phagocytic cells, and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Which of the following answers is not a mechanism pathogen use to survive within a phagocytic host cell?

• A. Withstanding the digestive and hydrolytic enzymes of the phagolysosome.
• B. Secreting digestive enzymes to lyse the phagocytic cells from the inside.
• C. Forming pores in the phagosomal membrane and escaping the phagosome.
• D. Creating proteins which blocks the fusion of the phagosome and lysosome.

Some encapsulated bacterial pathogens are said to be serum-resistant. Serum resistant pathogens avoid the effects of the complement system proteins. How are encapsulated bacteria able to be serum-resistant and avoid phagocytosis?

• A. The capsule ensures that C3b cannot bind the pathogen and trigger phagocytosis or opsonization.
• B. The capsule ensures that C3 convertase cannot trigger the activation of phagocytic immune cells.
• C. The capsule ensures that the pathogen will be able to escape the phagosome inside the phagocytic cell.