Immune System Collaboration - Online Tutor, Practice Problems & Exam Prep

Collaboration

Hi. In this video, I'm going to be talking about immune system collaboration. So when we get affected by an infection or some type of pathogen, it's not only one part of the immune system that responds, but all of it responds. So now I want to connect all these pieces together and figure out how are all these things activated, and how are they all responding. The innate immune system is responsible for first responding to a pathogen. This happens when you have some kind of pattern recognition receptor. For example, toll-like receptors are going to recognize the pathogen that's present in the blood, or on the skin, or wherever it is. This is going to activate these cells, usually causing these white blood cells or macrophages to take up the pathogen. They begin degrading it, and they eventually present it via these MHC molecules that we talked about. So now we have this infection, these cells have taken it up, and now they're presenting it on the surface. When they are presented, that begins to activate other cells. For example, dendritic cells are a type of antigen-presenting cell, they're part of the innate immune system that presents these antigens and activates these T helper cells. Once T helper cells are activated, they begin to secrete inflammatory molecules called cytokines. Cytokines have a lot of functions. There's a ton of them, and I'm going to talk about all of them. But essentially, they are inflammatory molecules. So what do they do? They promote inflammation. They increase the numbers of white blood cells around. They help the white blood cells migrate to the infection site, and they increase cell adhesion molecules so these white blood cells can attach to all the blood vessels and travel to the area where infection is and stay there until the infection resolves. So now we talked about how the dendritic cells are part of the innate immune system, but the T cells are part of the adaptive immune system. So, now those T helper cells are activated. So, they further inactivate the innate, which is what this is, but they also activate other cells that are part of the adaptive. These T helper cells come in two classes. The TH1 cells go on to activate macrophages, which I talked about, and the cytotoxic T cells, which go on to kill the internalized pathogens. Then you have the TH2 cells, which come in and activate B cells to secrete antibodies to target extracellular pathogens. So sort of the innate immune system activates the T helper cells, and those T helper cells go on to further activate the immune system, but also activate cytotoxic T cells, B cells, all these other cells that are important in the adaptive immune system. Here we have an APC, which could be like a dendritic cell. It takes up the antigen, chops it up, presents it via the MHC molecules to probably a T helper cell. The T helper cell then goes on and can release cytokines that go on to activate cytotoxic T cells. Where are they? Cytotoxic T cells. They can activate B cells to produce antibodies. They can activate more helper T cells, which release these cytokines here that help activating macrophages or other types of white blood cells that are super important. So this is a great example, not only of T cell development and the different T cell types but how the process of connecting the innate immune system to the adaptive immune system works when we are infected with something. Hopefully, that's clear. So with that, let's now move on.

Choose the following with the proper order of immune system activation.

• A. B cell → T cell → Dendritic cell → infection
• B. Infection → T cell → Dendritic cell → B cell
• C. Infection → dendritic cell → T cell → B cell
• D. Infection → B cell → dendritic cell → T cell