Eat healthy. There is no such thing as "boosting your immune system" with diet or supplements. All you can do is eat a well-balanced, healthy diet that provides the us rda of all of the vitamins we require, so the immune system has all the tools it needs to do its job as efficiently as it is intended to.
No magic pill. Many people are looking for some "magic pill" to "boost their immune system". There is no such pill. However, there is a way to boost your immune system, live a healthy lifestyle. Proper diet, proper sleep- wake cycles, healthy environment, proper exercise are the foundation of good health and good immune health. Supplements should be used selectively to supplement a healthy diet.