What feature of a virus helps induce an immune response in the body?

The feature of a virus that helps induce an immune response in the body is its antigens, which are specific molecules found on the virus's surface. These antigens are recognized by the immune system as foreign invaders, prompting the production of antibodies and activating immune cells to fight the infection. The recognition of viral antigens is crucial for the development of adaptive immunity, allowing the body to remember and respond more effectively to future infections by the same virus.