I'm currently researching th1/th2/th17 stuff in relation to AS and other diseases. Still learning so sorry if this sounds like gibberish.

What is interesting about diseases such as RA is that they involve overproduction on the th1 side. AS is relatively neutral as far as th1/th2 balance goes and is considered to be a th17 diseases. Other diseases like asthma overproduce the th2 side.

Oversimplification: The th1 side deals with intracellular bacteria & viruses whereas the th2 side deals with extracellular bacteria. Overproduction of th1 or th2 occurs at the expense of the other i.e. if th2 levels are high then th1 levels are low.

There is also trickery on the part of some bacteria and viruses in which they produce chemicals to trick the immune system into favouring a th1 or th2 response to avoid being killed by the immune system e.g. a virus which would be killed by the th1 side tricks the immune system into producing th2 instead which is not effective against it. The marshall protocol is based on this idea with the theory being that intracellular bacteria divert the immune system to overproducing th2.

What is interesting about LDN is that it has been shown to increase Th1 response and reduce Th2 response. From this you would think that LDN would be most effective at treating Th2 dominant diseases that involve Th1 deficiency as it would try and restore balance. What is intriguing is that it also seems to be effective for th1 dominant conditions. MS is a th1 dominant disease and so you would think that LDN would only exacerbate the imbalance but it appears to help.

Some wild speculation: This may be because th1 dominant diseases such as RA & MS are caused by intracellular bacteria and that the immune system is correctly increasing th1 to try and kill the infection. This could fit with the proteus mirabilis (intracellular?) theory of RA. The LDN may be providing the already dominant th1 side of immune system with an extra boost which helps it destroy the infection.

It also may be true that th1/th2 theory is rather useless as a target for treatment or as an insight into disease pathogenesis. LDN may also cause many more effects on the body than just increasing th1 and decreasing th2. I'm still pretty knew to all this stuff so apologise for any inaccuracies.