5) Avoiding Antibodies - Online Tutor, Practice Problems & Exam Prep

Bacteria have evolved several mechanisms to evade antibodies, including the production of IgA proteases, antigenic variation, and mimicking host cell molecules. IgA proteases degrade IgA antibodies in mucus membranes, hindering the adaptive immune response. Antigenic variation allows bacteria to alter surface antigens, preventing antibody binding. Additionally, some bacteria mimic host cell molecules, avoiding detection by the immune system. These strategies highlight the complex interactions between pathogens and host defenses, emphasizing the importance of understanding bacterial pathogenesis in immunology.

Intro to Avoiding Antibodies

In this video, we're going to begin discussing how some bacteria have evolved mechanisms to avoid antibodies. Recall from some of our previous lesson videos that during adaptive immunity, antibodies are going to be produced by plasma cells, and those antibodies will go on to tag pathogens and toxins for destruction by other immune cells. Now, there are several mechanisms that bacteria have evolved over time to avoid being bound by antibodies. Moving forward in our course, we're going to talk about some of those mechanisms in more detail. But for now, if we take a look at our image down below, notice that it is a map of our lesson on the mechanisms of avoiding antibodies that some bacteria use.

Some bacteria use IgA proteases to avoid antibodies. Others use a process called antigenic variation, which we'll talk more about moving forward. And others yet use another process of mimicking the host cells. We'll get to talk more details about each of these three mechanisms using IgA proteases, antigenic variation, and mimicking host cells as we move forward in our course. But for now, this here concludes our brief introduction to the fact that some bacteria are able to avoid antibodies and evade the immune system in that way. We'll learn more moving forward, and I'll see you all in our next video.

Bacteria Avoid Antibodies by Producing IgA Proteases

In this video, we're going to briefly discuss how some bacteria are able to avoid antibodies by producing IgA proteases. First, we need to recall from some of our previous lesson videos that IgA, or immunoglobulin A, is one of the 5 major classes of antibodies. Recall that IgA antibodies are primarily found in mucous membranes and other areas where mucus is secreted for protection. Mucous membranes serve as a protective barrier and are associated with local antibodies that tag pathogens for destruction.

Some bacteria are capable of producing IgA proteases. Proteases are enzymes that degrade other proteins. IgA proteases are enzymes that specifically degrade IgA antibodies found in the mucous membranes. By degrading the IgA antibodies, these bacteria are able to avoid the adaptive immune response. If we take a look at our image below, we can get a better understanding of how some bacteria capable of producing IgA proteases are able to degrade IgA antibodies in the mucus and thereby evade the adaptive immune response.

Notice that we have a figure of a person here, and we're specifically zooming into an area that has mucous membranes. Zooming into this area, you can see here we have the mucosal cells and the mucus embedded here. Notice that in the mucus, we have these IgA antibodies that are there to protect us from pathogens. If the pathogen, like the blue structure that you see here, is a pathogen that produces IgA proteases, such as these little red circles, then the IgA proteases will degrade all of the IgA antibodies and render them nonfunctional. Consequently, the degraded IgA antibodies are not able to tag these pathogens for destruction. Thus, these pathogens are able to evade the adaptive immune response by producing IgA proteases that degrade the IgA antibodies.

This concludes our brief lesson on how some bacteria are able to avoid antibodies by producing IgA proteases. We'll be able to get some practice applying this as we move forward and also learn more. So, I'll see you all in our next video.

All of the following are known mechanisms that pathogens use to avoid the effects of antibodies except which of these answers?

• A. Pathogens mimicking host cells.
• B. Fc receptors.
• C. Synthesis of IgG protease.
• D. Remaining intracellular.
• E. Antigenic variation.

Bacteria Avoid Antibodies by Antigenic Variation

In this video, we're going to talk about how some bacteria are able to avoid antibodies by a process known as antigenic variation. And so, once again, in order to avoid antibodies, some bacteria are able to constantly change or constantly alter their surface antigens in a process known as antigenic variation. And so, antigenic variation or changing or altering the surface antigens on the surface of a bacteria allows these bacteria to pretty much stay ahead of antibody production during the adaptive immune response. And this is because the antibodies that bind to one variation of an antigen on a pathogen will not be able to bind to a new one. And so, the bacteria stay ahead of the adaptive immune system by constantly changing its surface antigens. And so, if we take a look at our image down below, we can get a better understanding of antigenic variation and how some bacteria are able to avoid antibodies by, again, changing or altering their surface antigens. And so notice, over here on the left-hand side of our image, what we're showing you is a microbe here in blue, and this microbe on its surface has antigen A, which are these little blue triangles. And what you'll notice is that over here we're showing you an immune system cell, a B cell, coming and binding to antigen A on the surface of the pathogen. And so, you can see the B cell binds to antigen A on the microbe's surface. And so, of course, once this B cell binds and recognizes antigen A, it's going to become activated. It will proliferate and differentiate and become a plasma cell, and that plasma cell will be releasing thousands of antibodies per second, antibody A, which is specific for antigen A. However, notice that the microbe has gone and changed its surface antigens, and so there are no longer antigen A on its surface, now the microbe has antigen B on its surface. And so, what you'll notice is that the plasma cell produces antibody A, but antibody A does not bind to the new surface antigen B. And so, basically, the microbe here is staying, again, one step ahead of antibody production by changing its surface antigens. And so, then again, what might happen is another B cell might come around and bind to antigen B. And, the B cell will bind to the new antigen B, on the microbe surface. And, of course, that will cause it to differentiate and proliferate and form these plasma cells that are now secreting antibody B, which is again specific to antigen B. However, what you'll notice is that the microbe has once again changed its surface antigen. Now it has antigen C on its surface. And so again, the microbe is constantly changing its surface antigens to stay ahead of the adaptive immune response. And so notice here we're saying that the plasma cell produces antibody B, which is specific to antigen B, but now antibody B does not bind to the new surface antigen C. And so again, the microbe is staying ahead of the adaptive immune response by changing its surface to now having antigen C on its surface. And it is staying ahead of the antibody production. And so this is one way that bacteria are able to avoid antibodies through antigenic variation, 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.

Each year it is recommended that healthy adults get a flu shot. Why do we need to get a vaccine for the flu every year instead of once in our lifetime?

• A. The flu virus evolves new antigens very quickly.
• B. Each flu vaccine contains different flu antigens.
• C. The flu virus has antigenic variation each year.
• D. All of the above.

Bacteria Avoid Immune System by Mimicking Host Molecules

In this video, we're going to briefly talk about how some bacteria are able to avoid the immune system by cleverly mimicking host cell molecules. Some bacteria are able to produce surface antigens that are structurally similar to molecules found on our own host cells. We need to recall from some of our previous lesson videos that because of central and peripheral tolerance mechanisms, our immune system generally does not attack self cells, or molecules that resemble self cells. Therefore, any bacteria found mimicking self cells are not going to be targeted by our immune cells. Bacteria that are mimicking cell cells are able to avoid the immune system.

If we take a look at our image down below, we can get a better understanding of this idea. Take a look at how some bacteria are able to avoid the immune system by once again mimicking host cell molecules. Notice if we take a look at our left-hand side over here, in blue right here, what we have is a microbe, and over here in this purplish color, what we have is a host cell. You will notice that when we look at the bacterial surface antigens, which are these purple circles that you see here, they highly resemble the surface antigens or surface proteins of the host cell. This bacterial cell over here is somewhat mimicking the self cells. Here we have a bacterial pathogen mimicking the host cell. Because this bacterial cell is mimicking the host cell, the antibodies and the T cells are not going to be directed towards those bacterial surface antigens that are mimicking the host cell. This bacterial cell here is practically hiding with a costume that resembles the host cell.

If we take a look at the right-hand side of our image over here, notice that we have a host cell over here and we have another host cell over here. And then in the middle, we also have a host cell. Oh, wait a second. It's not actually a host cell. Notice that it's wearing a costume and this is actually a pathogen in disguise mimicking the neighboring host cells by producing these molecules that are very structurally similar to host cell molecules. Notice that it's day 8 and he's saying they still don't suspect. This concludes our brief lesson on this idea 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.

When pathogenic microbes possess surface antigens that mimic host cell proteins, they are able to avoid detection by antibodies and most immune cells. What stops the immune system from attacking these pathogens?

• A. The immune cells have central and peripheral tolerance to host proteins and cells.
• B. The immune cells cannot phagocytose the pathogens because they are encapsulated.
• C. The immune cells recognizes that microbes expressing proteins similar to host proteins are not a threat.

The host-pathogen 'arms race' is referring to:

• A. How quickly pathogens reproduce inside of a host.
• B. How pathogens attempt to evolve new ways to infect their hosts.
• C. How organisms attempt to evolve new ways to detect and fight infections.
• D. The combination of A and B.
• E. The combination of B and C.

IgA is an antibody specifically designed to protect mucous membranes. Why would mucous membranes need extra protect against pathogens?

• A. Pathogens can only infect a host through portals of entry that possess mucous.
• B. Our mucous membranes are commonly exposed to substances and pathogens from the outside world.
• C. Mucous membranes have significantly fewer immune cells to control pathogens than other tissues.
• D. Mucous is built to collect foreign substances and pathogens entering the body.
• E. A and B.
• F. B and D.
• G. C and D.

Here’s what students ask on this topic:

What are IgA proteases and how do they help bacteria evade the immune system?

IgA proteases are enzymes produced by some bacteria that specifically degrade IgA antibodies. IgA, or immunoglobulin A, is a class of antibodies primarily found in mucous membranes, where they play a crucial role in the immune defense by tagging pathogens for destruction. By producing IgA proteases, bacteria can degrade these IgA antibodies, rendering them nonfunctional. This degradation prevents the antibodies from tagging the bacteria, allowing the pathogens to evade the adaptive immune response. This mechanism is particularly effective in mucosal areas, such as the respiratory and gastrointestinal tracts, where IgA is abundant.

What is antigenic variation and how does it help bacteria avoid antibodies?

Antigenic variation is a process by which bacteria alter their surface antigens to evade the immune system. Surface antigens are molecules on the pathogen's surface that are recognized by antibodies. By constantly changing these antigens, bacteria can stay ahead of the adaptive immune response. When a B cell produces antibodies specific to one antigen, the bacteria can switch to a different antigen, making the existing antibodies ineffective. This continuous alteration prevents the immune system from effectively targeting the bacteria, allowing the pathogen to persist and evade destruction.

How do bacteria mimic host cell molecules to avoid the immune system?

Some bacteria evade the immune system by mimicking host cell molecules. They produce surface antigens that are structurally similar to molecules found on host cells. Due to central and peripheral tolerance mechanisms, the immune system generally does not attack self cells or molecules that resemble self cells. Therefore, bacteria that mimic host cells are not targeted by immune cells. This mimicry allows the bacteria to 'hide' from the immune system, avoiding detection and destruction. This strategy is akin to wearing a disguise, making it difficult for the immune system to distinguish between the pathogen and the host cells.

Why is understanding bacterial mechanisms for avoiding antibodies important in immunology?

Understanding bacterial mechanisms for avoiding antibodies is crucial in immunology because it helps us comprehend how pathogens evade the immune system and cause persistent infections. These mechanisms, such as IgA protease production, antigenic variation, and host cell mimicry, highlight the complex interactions between pathogens and host defenses. By studying these strategies, researchers can develop better therapeutic interventions, vaccines, and diagnostic tools to combat bacterial infections. Additionally, this knowledge aids in understanding the evolutionary arms race between pathogens and the immune system, providing insights into the development of immune evasion tactics.

What role do IgA antibodies play in the immune system?

IgA antibodies, or immunoglobulin A, play a crucial role in the immune system, particularly in mucosal areas such as the respiratory and gastrointestinal tracts. They are primarily found in mucous membranes and secretions like saliva, tears, and breast milk. IgA antibodies function by binding to pathogens and toxins, tagging them for destruction by other immune cells. This process helps prevent infections at mucosal surfaces, which are common entry points for pathogens. By neutralizing pathogens before they can invade deeper tissues, IgA antibodies are essential for maintaining mucosal immunity and overall health.