The main function of the immune system in the body is to defend against pathogens such as bacteria, viruses, and parasites. It recognizes and responds to foreign invaders through a complex network of cells, tissues, and organs. A robust immune system protects the body from infections and diseases by producing antibodies and activating immune cells. It plays a critical role in maintaining overall health and is influenced by factors such as nutrition, exercise, sleep, and stress levels, making a balanced lifestyle essential for optimal immune function.