has to do with timing the exposure of the receptors (opioid, I think) to a brief "shot" of the drug prior to the normal circadian timing of maximum endorphin release, which is apparently between 1:00 and 4:00 a.m. The brief inhibition by the drug apparently stimulates enhanced release of endorphin and production of additional receptors. The enhanced endorphin effect apparently has a regulatory effect on the intrinsic immune system.
This is the explanation given by Dr. Ian Zagon, the Penn State researcher who has done most of the work on the mechanism of low-dose naltrexone. There is a more complete description of this by Dr. Zagon on the LDN web site.
Robert