The components of the second line of defense against microbes may be characterized as:

• A. physical barriers such as skin and mucous membranes
• B. nonspecific cellular and chemical barriers
• C. adaptive immune responses involving T and B lymphocytes
• D. highly specific antibodies and memory cells

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the concept of the body's lines of defense against microbes. The first line of defense includes physical and chemical barriers that prevent pathogen entry, such as skin and mucous membranes.
2. Step 2: Recognize that the second line of defense is nonspecific and acts after pathogens have bypassed the first line. It involves cellular and chemical mechanisms that target a broad range of microbes without specificity.
3. Step 3: Identify components of the second line of defense, which include phagocytic cells (like macrophages and neutrophils), natural killer cells, inflammation, fever, and antimicrobial proteins such as complement.
4. Step 4: Differentiate the second line from the third line of defense, which is adaptive immunity involving specific responses by T and B lymphocytes, producing highly specific antibodies and memory cells.
5. Step 5: Conclude that the correct characterization of the second line of defense is 'nonspecific cellular and chemical barriers,' as it does not involve the specificity seen in adaptive immune responses.