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I was reading about Fab fragment and about using them to fight of viral infections. It seems that the Fab attaches to the viral receptors, which stops the viruses from attacking the cells. It seems that it has been done before. I was wondering, since Fab fragments can't activate immune response, what happens to the Fab-virus complex in the blood?

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  • $\begingroup$ What virus or virus family? Could you also provide us with a link to the paper you're reading? $\endgroup$ – Luigi Dec 17 '14 at 0:51
  • $\begingroup$ @Luigi hopefully as many possible viruses.. but the link I have talks about influenza virus $\endgroup$ – TanMath Dec 17 '14 at 0:53
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    $\begingroup$ @Luigi here is the link: jvi.asm.org/content/77/15/8322.full.pdf $\endgroup$ – TanMath Dec 17 '14 at 0:54
  • $\begingroup$ It won't trigger a full immune response since the Fc part of the antibody is needed for opsonization. $\endgroup$ – Chris Dec 17 '14 at 7:32
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There are three pathways by which soluble antibodies (which is what the Fab fragments arise from) can inactivate viruses (from Janeway's Immunobiology):

enter image description here

What you describe with the Fab binding to the viral receptors is a type of neutralization. Janeway claims that the type of naturally occurring antibody primarily responsibly for neutralization, IgA, is mostly exported to mucous secretions, so presumably it gets digested/excreted along with the rest of the mucous proteins.

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    $\begingroup$ I want more info about the section your book doesn't talk about... I want to know what happens to that complex...so unfortunately, you have not answered the question. $\endgroup$ – TanMath Dec 17 '14 at 2:57
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    $\begingroup$ For opsonization and complement activation the complete Ab is required (i.e. with the Fc fragment). But for neutralization I imagine the Fab is enough to prevent bacterial adherence. Maybe the poster can focus on this aspect. $\endgroup$ – ddiez Dec 17 '14 at 5:44
  • $\begingroup$ yes.. I agree with @ddiez (BTW, which page is this on?) $\endgroup$ – TanMath Dec 20 '14 at 0:35
  • $\begingroup$ oh.. I found the page.. (it's page 308) $\endgroup$ – TanMath Dec 20 '14 at 0:37

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