Prof. Edwards, earlier in the thread you said that the reason that IVIG is used is not to replenish IgG levels, but to replace the patient's IgG with a healthy person's IgG. I don't fully understand what you mean by this. IVIG was used in those Ritux patients with Hypogammaglobulinaemia - this would seem to be replenishing, since the aim is to get the patient's IgG levels to where they were before they were treated.
I also find it difficult to understand how diminished IgM and IgA levels are not important. I can sort of see why IgM might not be important, if the body is still able to produce IgM in response to a new infection (the question then is whether the B-cell depletion would significantly reduce this), but surely IgA is important, since this is the major immunoglobulin in the gut, and diminished levels would have an immediate impact on the immune system's regulation of the gut, wouldn't they?