Natural Immunity describes the state of being able to resist illnesses: such as a condition originates in a healthy immune system. This form of immunity is resistance that one inherits from one's parents. In contrast to acquired immunity, which one develops over the course of one's life. Acquired immunity comes when one has suffered from an illness : memory cells in the immune system essentially learn the illness and remember how to beat it in the future.
Vitamin C is vital component in maintaining a healthy immune system.