M Protein in S. pyogenes (antiphagocytic, but still induces Ab's)?

Jul 26, 2017
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I never understood this concept in medical school, but now I figured I'd put this to rest. I've asked many professors this question, but I seem to get more confused from the explanations. It's probably something very obvious I'm missing, but I don't know what it is.

When they say splenetic patients need to 'watch out' for encapsulated bugs (like s. pyogens, with it's capsule compopsed of M protein), i understand it's because the spleen is involved in removing these bugs from circulation. my understanding was that it does this, by coating these bugs with antibodies, which then get 'seen and plucked out' by the spleen (isn't this sort of like opsonization... and if it is, then i thought the M protein avoided opsoniztion, and therefore avaoided phagocytosis by splenic macrophages)

it's probably not that important, but this has always bugged me. does anybody have an explanation for this?
 
Jul 2, 2017
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1. Don't mix up strep. pneumonia from str. pyogenes.
2. m protein for strep. pyogenes -antibodies against strep. pyo. causes rheum fever. m protein nothing related with evade immune response.
3. strep. pneumonia has igA protease and capsule to evade immune system by avoiding opsonization and phagocytosis.
4. splenectomy means low IgM,hence Dec. complement activation, hence Dec. c3b opsonisation, hence encapsulated org.infection.
5. I am not that great, I referred everything back to books. hope it helps.
 
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Jul 26, 2017
4
1
Status (Visible)
  1. Medical Student (Accepted)
1. Don't mix up strep. pneumonia from str. pyogenes.
2. m protein for strep. pyogenes -antibodies against strep. pyo. causes rheum fever. m protein nothing related with evade immune response.
3. strep. pneumonia has igA protease and capsule to evade immune system by avoiding opsonization and phagocytosis.
4. splenectomy means low IgM,hence Dec. complement activation, hence Dec. c3b opsonisation, hence encapsulated org.infection.
5. I am not that great, I referred everything back to books. hope it helps.

Thanks Porcelain Gallbladder! Yes, I was definitely mixing up strep pneumo and strep pyogenes.

I understand now that the M protein of Strep Pyogenes is part of its cell wall. it's just that in the 'text books' (probably not necessary to know for step 1), it says that M protein inhibits complement, therefore inhibits phagocytosis (I'm assuming via invading opsonization). Again, it's probably not important for step 1, I've just always had a difficult time understanding this idea...

if our immune system is okay and well enough to make antibodies vs. the M protein, then why can't those same antibodies bind macrophages on their Fc portion, to opsonize, and phagocytose the bacteria too?

i'm probably missing something, but this one thing has always bugged me for a long time lol.

as for your post, thanks a lot, it definitely clears a lot of things up for me!
 
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