Antibodies can affect pathogens in a variety of different ways. One of which is called opsonization, which essentially is when pathogens that have antibodies bound to them are more easily targeted and removed by macrophages and neutrophils. Essentially, the antibody, which binds the antigen on the pathogen, makes it easier for the phagocytes to come over, identify, and then digest those particular pathogens. Now, antibodies can also neutralize and coat its exterior to the point where it basically can't function anymore. It can't infect a host cell because it's just covered in antibodies. It's like they form a shield around it, preventing it from interacting.
Agglutination, which is basically how antibodies can lead to clumping, occurs because antibodies, you might recall, are Y-shaped and they have two binding sites. Right? So, if one binding site binds one pathogen and another binds a different pathogen, and then another antibody binds that pathogen and another one, and so on and so forth, these antibodies can basically create big clumps of pathogens that are kind of just stuck in this matrix of antibodies. This leads to clumping and rendering these pathogens neutralized, and you can see this clumping happening here and here on these particular samples. So, this anti-A, anti-B, anti-D, that's referring to types of antibodies and basically what's happening is the anti-A antibody is causing agglutination in this sample, and the anti-D antibody is causing agglutination in this sample but the anti-B isn't binding. There's no binding there so no agglutination. But you can actually see the clumping; it's pretty wild, right? Like these samples should look like this sample for anti-B but, you can see that the material which would give it that solid color all the way through is all clumped together.
Lastly, we talked about complement proteins and the innate immune system and I said that not only can these be activated by pathogen-associated molecular patterns but they can be activated by antibodies to create holes in the adaptive immune system and are going to be part of the adaptive immune system and are going to respond to antibodies. Now, as I said, the adaptive immune system kind of has two sides to it. The cell-mediated response, which is going to occur through cell-to-cell contact and is mainly going to involve cytotoxic T cells which will be promoted by those Th1 cells. Remember, their job is to help activate those cytotoxic T cells and there's also the humoral response, which is going to occur in the blood and lymph or the humors of the body and it's going to involve antibodies being released from plasma cells which are promoted by those Th2 cells. So, those are basically the two aspects of the adaptive immune system.
Now, we have talked about what these effector cells do but remember there are also those memory cells being produced and their job is to deal with the secondary immune response. The primary immune response is what happens the first time you encounter an infection and antibodies are produced in response to that infection. And, as you can see, in a primary immune response, the amount of antibodies produced is not nearly as much as you see in a secondary immune response and that's because the system is actively trying to identify and fight this infection. The secondary immune response is so much more powerful and potent. You see there's less of a lag in the secondary immune response, the antibody concentration shoots up almost instantaneously because it's activating those memory cells. Those pathogens are activating those memory cells. Now, this all is part of what we'd call active immunity where you get an infection and produce antibodies as part of a primary or secondary immune response but it's worth noting that there's also what's called passive immunity, which is when you actually receive antibodies from another individual to help you deal with an infection. This is important because that's how fetuses deal with infections. Mothers will actually pass on antibodies to their fetuses to help them fight off any infections they've encountered while they are developing.
So, that's all I have for this page. Let's flip the page.
