Final answer:
C-reactive protein (CRP) is considered a crucial component of the second line of defense - innate immunity. The correct answer is option 2.
Step-by-step explanation:
C-Reactive Protein and the Immune System
C-reactive protein (CRP) is an acute-phase protein produced by the liver in response to inflammation, infection, and tissue damage. CRP is part of the innate immune system, acting as a non-specific marker that can indicate the presence of inflammation or infection in the body. It plays a significant role in the body's second line of defense against pathogens after the first line of defense, including physical and chemical barriers, has been breached.
The innate immune system responds with processes such as inflammation, phagocytosis by nonspecific leukocytes, and the secretion of immune factors and proteins. The second line of defense includes a variety of cells like macrophages, natural killer cells, several types of white blood cells, and protective proteins such as complement and interferon.
The complement system, which CRP can activate, contains about 20 proteins that cascade to mark and target pathogens for destruction. While the complement system is made in the liver and found in the blood plasma, it is actively involved in both the innate and adaptive immune responses, although it is not part of the early induced immune response. Moreover, its activation is considered part of the second line of defense.
In summary, C-reactive protein is considered a significant component of the second line of defense - innate immunity. From the options provided, the correct one is the second line of defense, which is innate immunity, where CRP plays a crucial role in the body's response to invading pathogens.