Are you making assumption that there maybe IgA antibody in the sweat or you actually have tested there is IgA in the sweat? There are two forms of IgA we learn in basic immunology. Most of IgA in the blood is a monomer, like molecular structure of IgG. In contrast, most IgA in the secretion (like in gastrointestinal tract) is a dimer. That dimer is formed with a secretory component that binds two units of IgA together. The sweat glands are built in skin. My feel is it is unlikely that you will find IgA in the sweat, especially the dimer of IgA if you agree the sweat is a from of secretion.

Shih-Wen Huang, MD

Dear Dr. Huang,

Thanks a lot for your answer.

I've not tested whether there is IgA in the sweat yet, but I as you mentioned, It seems it is common that there are IgA (dimeric form) in the sweat. (WIki: https://en.wikipedia.org/wiki/Immunoglobulin_A)

If it is true, my question was "Is there any possibility of anti-treponema pallidum IgA in the sweat, if the patient has anti-TP IgG, IgA, IgM in his/her blood?"

I wonder secretory IgA can also target a specific antigen, in this case TP, just like IgG or monomeric IgA in the blood :)

https://en.wikipedia.org/wiki/Immunoglobulin_A

I am not aware that secretory IgA -, dimer of IgA, can be found in the sweat gland. Even it is there, the amount would be very small. Please remember, the secretory IgA is produced locally and they do not get in the circulation. Well, in hypothetical term, if antibody is there, you should be able to measure it, be it anti-TP IgA or not. My question is,clinically if TP infection is a systemic one, why not just check antibody in the blood? What is the particular reason that you have to find secretory IgA against TP in the sweat?

Shih-Wen Huang,MD

Dear Dr. Huang,

My question assumed there are secretory IgA in the sweat. But well, if the assumption is suspicious, then I need to go back to the starting point and need to think again with a fundamental biology :)

Actually I am just a engineer, not a biology/medical expert. I was simply curious whether it is possible to do a rapid test (especially, STI screening test) via sweat, instead of blood, because it will be free from a painful blood drawing or finger prick.

Dr. Yoon,

You have a good thinking and is compassionate for the suffering of the patient.

I  could speak only from the standpoint of being a physician at the bedside. My bias are: 1. Can you collect adequate volume of sweat to measure secretory IgA against TP?  2. Treponema infection is a serious disease and is very likely a systemic infection. I would need an accurate result, not a controversial one, before I decide to treat this infection at length. Therefore, before you promote a sweat test for TP, you must first compare both the results of sweat test vs. the current blood test and make sure both tests match well with the results.

Shih-Wen Huang