The immune system is the body's defense network against harmful invaders like bacteria, viruses, fungi, parasites, toxic agents, therapeutic drugs and abnormal cells (such as cancer).

It is made of organs, cells, and proteins (antigens) that work together to recognize and eliminate harmful invaders like viruses, bacteria, parasites, and even abnormal cells such as cancer.

It also helps repair tissue damage and maintain overall balance in the body.

When the immune system malfunctions, it can lead to problems like autoimmune diseases (attacking the body's own tissues), allergies (overreacting to harmless substances), or immunodeficiency (being unable to fight infections effectively).