Antibodies in the Stomach?

[mrmandrake]

This was a question on a practice test:

Which of the following statements explains most plausibly why host antibodies are ineffective against H. pylori?

Answer: Antibody proteins may be denatured in the harsh environment of the stomach.

I thought that antibodies travel in the bloodstream, what would they be doing in the harsh environment of the GI lumen? Thanks for any help.

---

Members don't see this ad.

 

[JA Prufrock]

was it a passage based question? Did it tell you the H. pylori settled in the stomach? If so, it becomes a fairly straightforward question. Antibodies wouldn't be able to withstand the conditions of the GI lumen, so if they ever did travel there, they would be useless. You don't have to overthink it. If it doesn't tell you H. pylori was found in the stomach, it might be a little trickier. I haven't ever heard of H. pylori, but I guess there are a lot of bacteria that live in the stomach, so you might arrive at it that way.

 

[BusterDO]

H. pylori is found in the stomach, usually in the mucosa; it can withstand that environment. It is also the most common cause of peptic ulcer disease.

 

[mrmandrake]

was it a passage based question? Did it tell you the H. pylori settled in the stomach? If so, it becomes a fairly straightforward question. Antibodies wouldn't be able to withstand the conditions of the GI lumen, so if they ever did travel there, they would be useless. You don't have to overthink it. If it doesn't tell you H. pylori was found in the stomach, it might be a little trickier. I haven't ever heard of H. pylori, but I guess there are a lot of bacteria that live in the stomach, so you might arrive at it that way.

Yea it was passage based and it did imply that H. pylori is in the stomach, I was just thinking antibodies are useless because they never travel there, not because they travel there and then become denatured, so that answer was wrong to me. I chose an answer that had to do with the infection making the immune system weaker.

 

[JA Prufrock]

Yea it was passage based and it did imply that H. pylori is in the stomach, I was just thinking antibodies are useless because they never travel there, not because they travel there and then become denatured, so that answer was wrong to me. I chose an answer that had to do with the infection making the immune system weaker.

yeah, like I said, I think you just overthought it. This is an example of how the MCAT tests basic science but tries to confuse you at the same time. At its core the question only requires the knowledge of a couple basic principles:

1) antibodies are proteinaceous

2) proteins are denatured if the pH gets too low

3) The pH in the stomach is really low

The test wants you to overthink it like you did. I do see what you mean by antibodies traveling in the blood, and blood not entering the GI lumen, but keep things simple. I don't know the specifics of the immune system, but the question is assuming antibodies might enter the GI lumen in some way. Regardless, the MCAT wouldn't expect you to know that. Basic science, remember. It's easier for me since I already know the answer, but anyway, I'd just look out for these kinda traps.

 

[DrMattOglesby]

this is classic case of how intelligent people dont necessarily perform well on multiple choice exams!
good post.

 

[J ROD]

this is classic case of how intelligent people dont necessarily perform well on multiple choice exams!
good post.

True, true...I tend to overthink and miss them.

Like I say, I make A's inspite of myself. If I ever could guess right, I would have a great life like one of my friends.

 

[Vihsadas]

Yea it was passage based and it did imply that H. pylori is in the stomach, I was just thinking antibodies are useless because they never travel there, not because they travel there and then become denatured, so that answer was wrong to me. I chose an answer that had to do with the infection making the immune system weaker.

The question didn't indicate HOW these host antibodies would be delivered though. Yes, antibodies are normally delivered (almost always actually) by the bloodstream, but what if the antibodies were given directly via oral route in an experiment or clinical trial?

It's a tricky question, but if you realize that MCAT was most likely trying to test:
1) Whether you know that the acidic environment of the stomach can denature proteins
2) Whether you realize that an antibody is a type of protein and therefore would be denatured in the stomach.

This is the kind of 'extension of knowledge' question that the MCAT likes to test. Get comfortable with it!

Sometimes trying to figure out what the test maker is trying to test will help to reveal the correct answer.
GL.


EDIT: Moving to the Q&A forum.

 

[SketchLazy]

This was a question on a practice test:

Which of the following statements explains most plausibly why host antibodies are ineffective against H. pylori?

Answer: Antibody proteins may be denatured in the harsh environment of the stomach.

I thought that antibodies travel in the bloodstream, what would they be doing in the harsh environment of the GI lumen? Thanks for any help.

Some antibodies are secreted into all bodily fluids. A quick run down of the major immunoglobulins:

IgG - the most common antibody found in all fluids in all parts of the body
IgA - secreted into the lumen to protect exposed surfaces ie. eyes, respiratory tract, digestive tract, ears, nose etc.
IgE - secreted into the respiratory tract and mainly responsible for allergic reactions
IgM - found only in blood and lymph, involved in initial immune response

 

[RSAgator]

Though it can probably be argued, I believe the question asked how the bacteria evades the immune system. To me, evasion = avoiding detection. There was nothing to really indicate that the immune system was weakened by the bacteria and this doesn't answer the question as well as denaturation. Were the bacteria present in a different area of the body, it would be taken care of because the body does in fact develop antibodies against it hence no weakened immunity. However antibodies not being able to get to the bacteria for whatever reason constitutes evasion. Was a bit torn between the two as well and that was how I reasoned it.

 

[Kaustikos]

Some antibodies are secreted into all bodily fluids. A quick run down of the major immunoglobulins:

IgG - the most common antibody found in all fluids in all parts of the body
IgA - secreted into the lumen to protect exposed surfaces ie. eyes, respiratory tract, digestive tract, ears, nose etc.
IgE - secreted into the respiratory tract and mainly responsible for allergic reactions
IgM - found only in blood and lymph, involved in initial immune response

Exactly. Thank you microbiology for that one.

 

[werd]

for the sake of thoroughness, i thought i'd add that H. pylori colonizes the protective coating (mucus-like lining) of the stomach, and not the actual wall of the stomach; it's therefore not even technically in contact with your body, which makes detection and response by the immune system less likely or effective. colonization is usually a pretty chronic thing.

as noted above, the main secretory antibody is IgA, which is secreted in lungs/GI tract, etc. IgA deficiency is the most common immune deficiency, and presents with frequent pneumonia and GI infection in ppl that are otherwise not predisposed. werd.