Which of the following structures function as part of the innate immune defenses in animals? Select all that apply.

Innate immunity in animals relies on physical barriers like the skin and mucous membranes that stop microbes from entering. It also uses cells that eat invaders, such as macrophages and neutrophils, and proteins that circulate in blood, like the complement system, which attack and break down pathogens. Chemical signals called interferons and antimicrobial peptides help warn nearby cells and kill microbes. Together these components act immediately and do not need prior exposure, forming the first line of defense. For example, when bacteria touch the skin, the skin’s cells release antimicrobial peptides that destroy the bacteria before they can enter the body.