The following Nutrients play a major role in the immune system and can be found in a variety of foods that we use:

-Beta Carotene - Sweet Potatoes, Spinach, Carrots, mango, broccoli, and tomatoes
-Vit C - citrus fruits, berries, melons, tomatoes, bell peppers, and broccoli  
-Consider adding lemon pepper powder to sautéed veggies, or vegetable rice.
-Please add sautéed bell peppers, and onions while baking or cooking sausages. It cleanses the residues that sits in the colon.
-Vit D - fatty fish, milk, and eggs.
-Zinc - beans, nuts, and tofu
-Probiotics - yogurt
-Protein - milk, yogurt, eggs, chicken, seafood, nuts, seeds, beans, and lentils. -
-Eat healthy and get adequate sleep, and manage stress.
-Aim to eat 4-5 servings of fruits and vegetables.

https://www.eatright.org/health/wellness/preventing-illness/how-to-keep-your-immune-system-healthy