Respiratory problem of bronchitis like situation but coughing constant.?

my aunt has constant coughing problem since 10 years.she is suffering from allergic bronchitis type of problem.we tried many doctors and did lots of tests but still the same problem.now doctor is saying immune system is not working properly to protect against allergic reaction.we transfused blood to her many years back when she needed in pregnancy.pls. somebody suggest me proper solution.