What is the difference between synthetic peptide vs. peptide that is naturally made in the body?

[m25]

What is the difference between synthetic peptide vs. peptide that is naturally made in the body?
I came across this passage in TBR that basically said that synthetic peptide can act as antigen, but gave no reason. I thought the only difference between synthetically and naturally made peptide is how they are made. But since it says that synthetic peptide can act as antigen, I'm assuming that they actually differ in their chemical structure? If so, how do they differ?

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[Cawolf]

I am pretty sure that they are saying a synthetic peptide could act as an antigen, as opposed to introducing a natural peptide.

If there was some peptide toxin that caused disease, then a synthetic version could theoretically cause antibodies for the natural version to be developed. This would provide humoral immunity. If the synthetic version was deactivated or altered in some way, it could have none of the pathogenic effects of the actual protein while still conferring immunity.

This is how the vaccine for Diptheria toxin works - fun fact, that was the first synthetic vaccine produced.

 

[m25]

I am pretty sure that they are saying a synthetic peptide could act as an antigen, as opposed to introducing a natural peptide.

If there was some peptide toxin that caused disease, then a synthetic version could theoretically cause antibodies for the natural version to be developed. This would provide humoral immunity. If the synthetic version was deactivated or altered in some way, it could have none of the pathogenic effects of the actual protein while still conferring immunity.

This is how the vaccine for Diptheria toxin works - fun fact, that was the first synthetic vaccine produced.

Wait I am confused-so the synthetic peptide that they said can act as antigen was actually a synthetic hCG peptide, which is a nontoxic hormone(as it would naturally exist in pregnant women).
According to what you have said, the synthetic peptide has to be a toxin in order to act as antigen. But synthetic hCG peptide is not a toxin, so how can it act as antigen?

 

[Cawolf]

No, I didn't say it had to be a toxin - I said it could be.

An antigen is any "marker" that identifies something.

 

[MassFX]

To be clear, both synthetic peptides and natural peptides can act as antigens. Natural peptides produced in your own body hopefully do not act as antigens. If you do form antibodies to your own natural peptides, the result is an autoimmune disorder. Natural peptides made by natural viruses hopefully do act as antigens, and that helps you fight the virus.

A synthetic peptide designed to be a replica of a natural peptide may or may not be chemically indistinguishable. For instance, the peptide hormone insulin is hard to duplicate precisely because of its secondary and tertiary structure. As a result, human diabetics can choose between synthetic insulin (recombinant human insulin) and porcine insulin (removed from pig carcasses), and these different kinds of insulin have different pharmacological properties.

A very simple peptide with no post-translational modification and no secondary or tertiary structure would probably be totally chemically identical in the natural and synthetic forms. It could still serve as an antigen, because both natural and synthetic peptides can serve as antigens. However, many peptides do not tend to generate antibodies, for a variety of reasons.