Question 1

What are the two main types of cells involved in innate immune responses?

Accepted Answer

The innate immune response relies on phagocytes and natural killer (NK) cells. Phagocytes, including microphages and macrophages, engulf foreign particles and cellular debris through phagocytosis. NK cells are large granular lymphocytes that directly recognize and eliminate infected or cancerous cells by inducing apoptosis without engulfing pathogens.

Question 2

How do neutrophils and macrophages differ in their roles during infection?

Accepted Answer

Neutrophils are abundant, mobile microphages that serve as first responders to infection, quickly engulfing bacteria and cellular debris. Macrophages are larger phagocytes derived from monocytes that arrive after neutrophils. Wandering macrophages patrol tissues, while fixed macrophages like Kupffer cells in the liver remain permanently stationed to capture pathogens that bypass initial defenses.

Question 3

What is phagocytosis and how does it eliminate pathogens?

Accepted Answer

Phagocytosis is a multi-step process where phagocytes recognize and bind foreign particles through surface receptors, then extend their membrane around the particle to form a phagosome. The phagosome merges with lysosomes to create a phagolysosome, where enzymes break down and destroy the pathogen. Remnants are expelled, completing the elimination process.

Question 4

How do NK cells recognize and eliminate infected or cancerous cells?

Accepted Answer

NK cells detect infected or cancerous cells by recognizing reduced levels of major histocompatibility complex (MHC) class I molecules and stress-induced molecules on cell surfaces. Upon recognition, NK cells release cytotoxic granules containing perforin and granzymes that induce apoptosis in target cells, allowing rapid response to infections without engulfing pathogens.

Question 5

What distinguishes NK cells from B and T lymphocytes in immune function?

Accepted Answer

Unlike B and T lymphocytes, NK cells lack specificity and recognize a wide range of targets through pattern recognition rather than antigen-specific receptors. NK cells comprise 5-10% of blood and lymph lymphocytes and respond immediately to infected or cancerous cells by inducing apoptosis, making them part of the rapid innate immune response.

Question 6

What is the monocyte-macrophage system and why is it important?

Accepted Answer

The monocyte-macrophage system, also called the reticuloendothelial system, is an extensive network of phagocytes distributed throughout the body. This system provides continuous immune surveillance by removing cellular debris and responding to pathogen invasion before adaptive immunity activates. It includes circulating monocytes and tissue-resident macrophages positioned strategically in organs.

Question 7

How do eosinophils contribute to the innate immune response?

Accepted Answer

Eosinophils are less abundant microphages that circulate in the blood and target foreign substances or pathogens coated with antibodies or complement proteins. They leave the bloodstream to enter peripheral tissues affected by injury or infection, providing specialized phagocytic defense against specific pathogenic threats identified by immune markers.

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