Hi Barbara - I have had a lot of help from this site, so it's great to be able to encourage someone else.
I believe the gamma globulin infusions boost my immune system. They don't raise my white cells/neuts/lymphs but I'm sure they help me to avoid infections. See
http://www.utoronto.ca/kids/Hypogam.htm for more info on hypogammaglobulinaemia. Also I don't get as tired or have as many aches and pains (hips, shoulder) and I therefore sleep better when I'm having the infusions.
Your husband may be able to do a couple of other things to avoid infections. My ANC is usually a lot lower than 900 - often only half that. However, since diagnosis with MDS I have only had 1 bladder and 2 chest infections - better than before I was diagnosed. A couple of other things I do which I believe help: I avoid foods containing added sweetening (sugar, maple syrup, etc) except for honey and stevia. If I feel the slightest hint of a sore throat I take 5000 mg Echinacea (capsule) and continue this a couple of times a day until the soreness disappears. The idea is to knock it before it goes to your chest. I believe being dairy free also helps because sugar + dairy creates phlegm and I think that phlegm is probably a good breeding ground for germs. With the bladder, I take 15,000 cranberry capsules if there is the slightest hint of it and this works too.
Best wishes! Will be interested to follow your posts as your husband is also the only other person I've come across so far with hypogammaglobulinaemia + predominating white cell problems.