I have the flu, dry cough, minimal wheezing. The doctor wants me to take prednisone. If prednisone lowers immune system, isn't it a bad idea to take?

Balance. There are always risks and benefits to medications. Did your doctor exaplain why s/he wants you to take it? If you have a history of asthma, it may have been to prevent you from tipping into a full attack. Call your doctor or go for another visit to talk about it. If you don't get the answers you feel like you need, consider another doctor since educating you is part of our job!
Prednisone wheezing. Your doctor has prescribed Prednisone because you are wheezing, and may have underlying asthma.Normally with flu we do not use prednisone.Having said that short courses of steroids like Prednisone have no effect on the immune system and are prescribed all the time.If you have concerns, talk to your doctor and you can use inhaled steroids which work as well, but I am not secong guessing your doctor.