Steve is a construction worker. he cut his hand deeply. the cut then became infected. which line of immune defense was broken in his immune system? when steve cut his hand, his line of defense was broken.

When Steve cut his hand, his Epidermis/skin line of defense was broken.

Explanation:

The epidermis is the most superficial layer of the skin, in contact with the environment. It is formed by stratified squamous and keratinized epithelial tissue. Its name derives from the Greek words epi, which means above and dermis, which means skin. So, it means above the skin.

The functions of the epidermis are:

When Steve cut his hand, he injured his epidermis, and broke through that protective barrier. This opened up an opportunity for microorganisms to infect their injury.