Video Transcript
The figure shows part of the process of phagocytosis in a macrophage. What is present in subcellular structure X? (A) Complement proteins, (B) hydrolytic enzymes, (C) interferons, (D) histamine, (E)
cytokines.
The immune system is a network of cells and proteins that defend us against
infection. It can be divided into innate, or nonspecific, immunity and adaptive, or specific,
immunity. This question is asking us about innate immunity. So let’s describe that in some detail.
Innate immunity is the first line of defense while the adaptive response
develops. It is rapid and includes barriers like our skin that can prevent pathogens from
entering and causing infection. Innate immunity is nonspecific, meaning it fights all pathogens in the same way. If pathogens do enter our body, for instance, if you get a cut, then specialized
cells called phagocytes can work to eliminate them from our body.
There are different types of phagocytes. But a well-known example is the macrophage, which we can see here. Macrophages are called phagocytes because they undergo phagocytosis. Phagocytosis is a cellular process where pathogens and other small particles can be
engulfed and destroyed by the phagocyte.
Phagocytosis begins with the macrophage binding to the pathogen. The macrophage has special receptors that recognize conserved surface proteins on
many pathogens. Then the pathogen begins to be engulfed by the macrophage. Here, the pathogen has been engulfed by the macrophage. Notice that a vesicle has formed around the pathogen. This is called a phagosome.
Next, the pathogen needs to be destroyed. To do this, organelles within the macrophage, called lysosomes, fuse with the
phagosome. Within the lysosome are digestive enzymes, or hydrolytic enzymes, that can break down
the components of the pathogen. These broken down components can then be released from the macrophage or presented on
their cell surface for use in the adaptive immune response.
So now if we go back to our question, we can see that the subcellular structure
that’s labeled X is given by answer choice (B), hydrolytic enzymes.
