I'm with you on that. I've got an immunodeficiency disorder, I've had it since birth but didn't even know I had it. When I was 33 it kicked me like a Mule. I was weeks away from Kidney and Liver failure. It was so bad that my Doctor told me to stop drinking but I gave up Alcohol 12 years before. I've been tee total for 30 years (bar 2-3 celebrations) next Month. He put me on Prednisone. Smoking at the time helped settle my system also, I'm guessing it's the stimulant side of Nicotine more than anything.
I've given up Smoking, Alcohol, Caffeine and eating Red Meat but Nicotine is here to stay for me, I'm down to 1% but I can feel it helping my immune system, it also helps with preventing Chronic Fatigue, for me.
Funny story, I once convinced a friend in School (he wasn't the sharpest Tool in the box) that Nicotine was invented by an Irish man called Nick O'Tierney