Why does lack of sleep hurt your immune system?

Alters body rhythm?: A body that is very fatigued, due to a lack of sleep, excess stress, being overworked, etc..., may get sick more easily. This concept is difficult to prove. Maybe a person's internal biological rhythm is disrupted, leading to changes in one's natural cortisol levels, which will alter one's immune system functioning and change the ways his body responds to additional stress.

Sleep and immunity: Sleep does play a big role with many systems in our body. It does not actually get weaker it is simply that if the body is tired, the defense systems within the body will not be as alert.