The immune system is boosted by a healthy lifestyle. A healthy body signifies a healthy immune system. One common thing that weakens the immune system is stress. Our bodies recuperate whenever we have enough rest. This means that, when the body is not given enough rest when it needs, every aspects of the body gets affected. And the more rest is deprived the body, the weaker the defence system of the body gets
Another thing that can weaken a person's immune system is poor dieting. We should know what our bodies need in terms of nutritional requirements and feed it with such. The body needs a balanced diet to function and stay healthy. If you can feed your body right, you won't have any problem with your immune system.
So to me, I think adequate rest when the body needs it and a healthy diet will always keep our immune systems strong