Question

Which of the following is NOT an example of a nonspecific defense mechanism? A. Skin provides a physical barrier against invasion. B. Macrophages engulf and destroy foreign particles. C. An inflammatory response is initiated in response to physical damage. D. Cytotoxic T-cells destroy foreign antigens.

Short answer

D. Cytotoxic T-cells destroy foreign antigens.

Step-by-step solution

- Identify each defense mechanism

Read the descriptions for each option to understand the type of defense mechanism it represents.

- Recognize nonspecific defense mechanisms

Nonspecific defense mechanisms include barriers like skin, inflammatory responses, and cells like macrophages that attack any foreign particles without specificity.

- Analyze Option A

Option A: Skin provides a physical barrier against invasion. This is a nonspecific defense mechanism because it blocks any pathogen without targeting specific invaders.

- Analyze Option B

Option B: Macrophages engulf and destroy foreign particles. This is also nonspecific because macrophages attack any foreign substance in a general manner.

- Analyze Option C

Option C: An inflammatory response is initiated in response to physical damage. This mechanism also doesn't target specific pathogens, making it nonspecific.

- Analyze Option D

Option D: Cytotoxic T-cells destroy foreign antigens. This is a specific defense mechanism because Cytotoxic T-cells target and destroy cells exhibiting specific antigens.

- Identify the correct choice

The correct answer is the one that represents a specific defense mechanism.

Key concepts

nonspecific defenses

The immune system has two main types of defenses: specific and nonspecific. Nonspecific defenses are the first line of defense and are always ready to protect the body against any pathogen. These defenses do not differentiate between types of pathogens. They simply act against all invaders in a general manner.
Nonspecific defenses include various mechanisms and structures:

• Physical barriers like skin and mucous membranes
• Cells such as macrophages and natural killer cells
• Processes like the inflammatory response

These mechanisms are crucial because they offer immediate protection and help prevent infections from getting a foothold in the body.

skin barrier

The skin acts as one of the most essential nonspecific defenses in the body. It provides a physical barrier that keeps microbes at bay. The outer layer of skin, known as the epidermis, is made up of tightly packed cells and keratin, which is tough and water-resistant. This layer acts like a wall that most pathogens can't penetrate.
Several features make the skin an effective barrier:

• The skin is slightly acidic, which creates an inhospitable environment for many bacteria
• It constantly sheds dead cells, removing microbes that try to cling to the surface
• Skin produces sebum, an oily substance that can kill bacteria

By maintaining this robust barrier, the skin helps protect the body from a wide range of infections.

macrophages

Macrophages are a type of white blood cell and form a vital part of nonspecific defenses. They patrol the body, looking for foreign particles like bacteria and viruses. When they find these invaders, they engulf and digest them in a process called phagocytosis. This not only destroys the pathogens but also helps alert other parts of the immune system of the invasion.
Some key features of macrophages include:

• They can recognize and attack a wide variety of pathogens without needing to identify specific targets
• They release chemicals that attract other immune cells to the site of infection
• They play a role in activating specific immune responses after initial detection

Overall, macrophages are like the body's internal patrol officers, constantly on the lookout for anything harmful.

inflammatory response

The inflammatory response is another critical component of the body's nonspecific defenses. When the body detects physical damage or infection, it triggers inflammation to contain the issue and promote healing. This response involves the release of various chemicals that increase blood flow to the affected area.
What happens during inflammation:

• Blood vessels dilate, leading to redness and warmth
• Fluid and immune cells leak into tissues, causing swelling
• White blood cells like macrophages rush to the site to fight off pathogens

Inflammation is beneficial because it helps isolate the infection, making it easier for immune cells to destroy the pathogens. However, chronic inflammation can be harmful, which is why the body carefully regulates this response.