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From a research paper:

FOLR1 autoantibody detection
The assay for identification of the presence and relative quantification of FOLR1 autoantibodies in serum samples was performed as previously published.41–43 Horseradish peroxidase (HRP) labelled anti IgG antibody (Cat#I8640 Sigma Aldrich) and IgM antibody (Cat#I8260, Sigma Aldrich) were used to detect IgG and IgM. Antibody-depleted sera (Sigma Aldrich) was used as negative control. Serum effect on blocking FA binding to folate binding protein was detected using HRP labelled FA (FA-HRP, Ortho-Clinical Diagnostics, Raritan, New Jersey, USA). FA in serum samples was removed as previously described. Unlabelled FA was spiked (0.01–2000 ng/mL) into stripped antibody depleted sera to generate the standard curve. The SuperSignal ELISA Femto Substrate (Cat#37074, ThermoFisher Scientific) was used as substrate for detection of HRP activity. Images were collected using a 96-well imager (Q-View Imager, Quansys Biosciences). Intensities were extracted from the images using Q-View Software. IgG, IgM and relative FA-blocking amount were calculated based on the standard curves.

What is the meaning of "stripped" in stripped antibody depleted sera? I think that "antibody-depleted sera" stands for "serum samples that contain a reduced concentration of antibodies". But why stripped? Does it mean that the authors applied some additional techniques to ensure an even lower level of antibodies in the serum samples?

I found it odd because the word "stripped" is used only in this particular place, and nowhere else. They mention 'antibody-depleted sera" earlier, without "stripped".

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    $\begingroup$ I think the word "stripped" refers to the depletion of FA (folic acid?). The previous sentence is "FA in serum samples was removed as previously described." They were probably clarifying that the standard was made using antibody-depleted, FA-depleted (stripped) serum. $\endgroup$ – MattDMo Dec 31 '20 at 20:54
  • $\begingroup$ @MattDMo - thank you! Indeed, in a paper referenced in "as previously described", a charcoal stripping method for removal of folic acid is described. You might post your comment as an answer, it was the correct guess! $\endgroup$ – CopperKettle Jan 3 at 4:52
  • $\begingroup$ All set - I posted an answer below. $\endgroup$ – MattDMo Jan 3 at 17:36
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While @mgkrebbs is correct in their answer that the meaning of "stripped" cannot be 100% determined without corresponding with the author, there are clues that point to a most likely answer.

The previous sentence, "FA in serum samples was removed as previously described", cites this reference, which describes testing of different materials for their efficacy in removing radiolabeled folic acid from serum. I don't have access to the full text of that article, but according to the original poster of this question, this method was called "charcoal stripping."

The term "stripped" is also commonly understood in the lab as referring to some reagent which has had some component(s) of its makeup removed intentionally. The two uses I'm familiar with are this scenario, where some component of serum is removed (usually with charcoal), and western blotting, where stripping refers to the process of removing the bound antibodies from the membrane so that it can be reprobed with different ones.

So, with no other depletion method being mentioned aside from the antibody depleted serum purchased from Sigma, the arrangement of sentences, and the reference to charcoal stripping, I think it's safe to assume that "stripped antibody depleted sera" refers to the Sigma reagent which has undergone the folic acid removal process.

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I believe this is a failure of editing, and the meaning in this paper of "stripped" cannot be determined without correspondence with an author. "Stripped" is an informal term for either removal of some substance or treatment with a material such as charcoal which affects many substances. Normally in papers "stripped" is qualified (at least initially) to indicate the type of treatment. Here it could plausibly refer to antibodies, folic acid, or any number of other things. It may be an artifact of draft editing that was meant to replace "stripped" with "antibody depleted" as a more precise term. I suggest writing the corresponding author.

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