In the Ab titer data there is a column for unit, when/why is there a change in the unit and why does it appear for just IgE with total antigen?
Thanks!
Hi @joreyna,
For IgE we had two types of measures:
- Ag specific (PT, FHA…)
- Total IgE --> Regardless of the antigen, we measured the total amount of IgE in plasma.
Thus, the Ag-specific data presented is in MFI units. This MFI is the fluorescence that the equipment captures (as a readout of the amount of antibody present in plasma). This measure is not quantitative but qualitative of Ag-specific IgE in plasma.
Regarding the total antigen: The only antibody that it was measured as a total was IgE this is why TOTAL only appears there. For the rest, we did not measure non-antigen specific levels.
Regarding the Units: Both are quantitative measures but they are slightly different. mg/ml only indicates the concentration of the protein in the plasma, while IU is more based on the activity of the molecule. This unit is typically used in enzymes and molecules with biological activity and it is always based on assays of the biological effect of the molecule. In our case, this is based on units defined by the WHO. I will have to dig more into the exact conversion in our case, as we are acquiring the serum with all the specifications in the next few days.
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Hi Ferran,
Thanks for you detailed response. I have one new question, if MFI is qualitative then how do we obtain quantitative values in the form of mg/ml and IU/ml?
Hi Joaquin,
The way that this was performed was including standards for quantification purposes for certain measures such as IgG for PT, PRN…
However, the majority of data generated was given as an MFI value. This data is usually used and it does not require its transformation to quantitative values. In our paper in revision we used the data to track the variation in levels of each of the antibody isotypes against each of the antigens.
This variation of antibodies in plasma can be studied using either MFI and/or mg/ml, UI/ml, but for example, 100 UI/ml of PT specific IgG are used in clinical settings to determine a potential recent exposure to the pathogen. I mean that this gives us extra information also for other purposes.
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Here a clearer explanation on how the units were reported:
“PT-, PRN- and FHA-specific IgG positive beads were calculated as IU/mL based on the WHO reference serum. Other antigen-specific IgGs that had no reference standard or antigen-specific IgE, IgG1, IgG2, IgG3, and IgG4 -positive beads are reported as log10 of the median fluorescent intensity (MFI).”
And yes, PT for IgG is equivalent to the 1% PFA PT which we have to modify in our database.
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I see, I think we should also try to add documentation on these types of things. For now the Swagger documentation (https://staging.cmi-pb.org/docs/api/) is great for accessing the data but it doesn’t have general information, something like a Dream Challenge has (https://www.synapse.org/#!Synapse:syn21849255/wiki/602409). Something nuanced like ab titers units is tricky to understand and I would imagine some people would mistakenly filter out some data.
I just wanted to mention that the current database doesn’t have any log10(MFI) values. Antigen-specific IgE, IgG1, IgG2, IgG3, and IgG4 use IU/ml values so should the units be changed to log10(MFI)?
And I see what you mean about PT for IgG equals 1% PFA PT 
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You are totally right and we will discuss this, but it makes complete sense that datasets are well explained. The researchers will greatly benefit from a detailed explanation of the origin of all the data.
Apart from this, we will unify all the names and also work on a consistent reporting of units. In the next dataset, we will include MFIs for the IgG PT, IgG PRN and IgG FHA for which now we only have the IU/ml.
Again, thanks @joreyna for the input, these are all great ideas and points to make it all much better.
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