That's a great question. I'm not sure, but maybe it's adrenal? I do know that early, mid stage adrenal fatigue the immune system gets suppressed. In the later stages of adrenal fatigue, the immune system runs around unchecked causing autoimmune issues. However, I have autoimmune issues and my WBC counts have always come back normal too. I don't get it. I've wondered the same thing. I did a little looking around and so far have found nothing.