@minkeygirl
@SOC
I wonder if SOC could tell us more about this.
Not really, I'm no immunologist.
But here's the best I can do with layman's knowledge and language.
When you first get an infection you produce IgM antibodies. These are relatively short-lived, so IgM titres are only high after a recent infection or possibly a re-exposure. Slightly later your body produces IgG antibodies which continue in your body for decades. This is what confers immunity to many infections once you've had them. The fact that IgG antibodies continue is why some doctors not up on the details think high IgG titres
only mean you've been exposed to the infection. The detail they forget or ignore is that IgG titres diminish slowly over time which is why we sometimes need booster vaccines. For example, some people develop shingles because their antibodies to VZV have diminished to the point where they no longer have sufficient IgG antibodies to VZV(aka Human Herpesvirus 3, aka HHV-3, aka chicken pox virus). The so-called shingles vaccine is a chicken pox booster.
So IgG titres are not a measure of current or recent infection. They don't change quickly. However, high IgG titres in a person decades past their first infection is not expected. Titres should be decreasing slowly. This doesn't mean
any positive titre is suggestive of an on-going or recent infection, but
unusually high titres for your situation (age, time since original infection) could be.
So in certain cases high IgG titres are suggestive of the immune system's need to produce an increased number of antibodies, for example in an active infection. So while a high titre in certain cases may suggest an on-going infection, treatment will not cause the IgG antibodies to drop rapidly. That's not the way IgG antibodies work. They hang around waiting to fight off any new exposures and only diminish slowly when they have not been needed for a long time. OTOH, if IgG titres are climbing, not diminishing, that suggests your body is trying to fight off the infection and is sending in the troops. So, while IgG titres are not particularly useful for measuring treatment success, they can, in certain circumstances, help to diagnose on-going or recurrent infections. That said,
in some cases IgG titres will drop noticeably over several months, but it's not something that happens in every patient in every case, so you can't assume your titres will drop significantly within months of treatment.
On the other side of the coin, antibodies are produced by B-cells. If, for some reason your B-cells are unable to produce antibodies properly or in sufficient numbers, you could have low or normal antibody titres even if you have an active infection that would, in a healthy person, be controlled by an increase in IgG antibodies. In that case you could have an active infection but not high IgG titres.
IgG titres are not an absolute indicator and are not easily interpreted in isolation by a layperson (or a good many doctors, for that matter). They are one of several clues used by knowledgeable doctors to interpret immune or infection status.
Bottom line: IgG titres have their uses, but measuring short-term treatment success is generally not one of them.
