Human immune system and pathogens can coevolve. A good example is human immunodeficiency virus (HIV). The reverse transcriptase enzyme of HIV has a low accuracy and this causes increases the rate of mutation in this virus. Then, natural selection favours the mutants that can escape human immune system and cytotoxic T cells. This will help the virus to reproduce and infect the person. On the other hand, human immune system reacts to this process and evolves to protect the person and remove the virus from the body (2).
It has not been proven yet that there is a link between human lifestyle and evolution of human immune system, but there are ongoing researches on diet, exercise, age, psychological stress, herbal supplements, and other factors and their possible link to coevolution of immune system with them (11).