The substances responsible for green and purple color of broccoli, vitamin C, beta-carotene and other vitamins and minerals, particularly selenium, copper, zinc, phosphorus, etc., present in broccoli are really great immune-strengtheners. They protect you from numerous infections.
Carrots do wonders for boosting the immune system by increasing the production and performance of white blood cells; building resistant to various kinds of infections.
Asparagus is one of the richest sources of rutin (a natural substance found in plants) which together with vitamin C, can help to energize and protect the body from infections. Asparagus is also a source of iron, which boosts the immune system and prevents anaemia.
The anti-oxidant nutrients in pears are a great way to boost your immune system. Drink pear juice at the first sign of a cold.