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I have a protein that is produced with the baculovirus system that is recognized by antibodies generated by immunization of rabbits with the same protein produced in E. coli. However the baculovirus protein did not induce an antibody response when I immunized some pigs.

Could it be that the baculovirus protein is not immunogenic? Even if the same protein is recognized by antibodies? If the rabbits produced antibodies with a protein that did not have post-translational modifications, how can not be immunogenic when the modifications are added?

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  • $\begingroup$ What kind of protein is this? A protein from pigs? Or one which is at least a highly homologous with a pig protein? $\endgroup$ – Chris Oct 20 '16 at 9:27
  • $\begingroup$ Did you add some special tags in your bacterial expression system? It is possible that the original baculovirus protein does not elicit immune reaction because it mimics a host protein. Many viruses use this strategy to evade immune response. The bacteria-expressed protein may have folded differently leading to the loss of the molecular mimicry. $\endgroup$ – WYSIWYG Oct 20 '16 at 9:52
  • $\begingroup$ it is a viral protein. I infected rabbits with the E. coli version and I got an immune response; the baculovirus version instead did not elicit a response in pigs. I used adjuvants to infects pigs $\endgroup$ – Gigiux Oct 20 '16 at 20:38
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Pure proteins are often poorly immunogenic because you need to have some kind of "adjuvant" effect to induce a strong effect. Bacterially-produced proteins may well have some bacterial LPS or other immune stimulants still present after purification which would drive a much stronger response than the same protein produced from eukaryotic cells. There are many other possible explanations -- one or the other protein may have aggregated or misfolded, which could drive a different response, for example.

In other words the effect you're seeing may be annoying but is not particularly shocking, and you have no choice but to do some routine troubleshooting at this point. Is your protein more immunogenic when administered with an adjuvant? Are the two versions identically folded? Are there antibodies present to a misfolded form that you're not detecting? And so on.

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  • $\begingroup$ Thanks, different folding was also my guess. I did not consider the LPS residual though. $\endgroup$ – Gigiux Oct 20 '16 at 20:43
  • $\begingroup$ @Gigiux If this answer addressed your problem, please consider accepting it by clicking on the check mark/tick to the left of the answer, turning it green. This marks the question as resolved to your satisfaction, and awards reputation both to you and the person who answered. If you have >= 15 reputation points, you may also upvote the answer if you wish. There is no obligation to do either. $\endgroup$ – MattDMo Oct 21 '16 at 14:03

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