Which of the following is the first line of defense against a microbial infection in the human body?

• A. Intact skin and mucous membranes
• B. Production of antibodies by B cells
• C. Release of interferons by infected cells
• D. Activation of cytotoxic T cells

Answer: (A)

Verified step by step guidance

1. Understand that the human body's defense against microbial infection is organized into multiple lines of defense: the first line, second line, and third line.
2. Recognize that the first line of defense consists of physical and chemical barriers that prevent pathogens from entering the body, such as intact skin and mucous membranes.
3. Note that production of antibodies by B cells and activation of cytotoxic T cells are part of the adaptive immune response, which is considered the third line of defense.
4. Identify that the release of interferons by infected cells is part of the innate immune response, specifically a second line of defense mechanism that acts after pathogens have bypassed the first line.
5. Conclude that since intact skin and mucous membranes act as physical barriers preventing entry of microbes, they represent the first line of defense against microbial infection.