Question 1

Which of the following best describes the primary function of macrophages in the innate immune system?

Accepted Answer

They engulf and destroy microbes through phagocytosis.

Question 2

A patient with a severe viral infection is found to have elevated levels of interferons. What is the most likely effect of these proteins?

Accepted Answer

Interferons inhibit viral reproduction and activate macrophages.

Question 3

Which of the following is a key difference between innate and acquired immunity?

Accepted Answer

Innate immunity is present at birth, while acquired immunity develops after exposure to pathogens.

Question 4

The skin acts as a barrier to pathogens partly because its secretions maintain a pH between 3 and 5. What is the significance of this acidic environment?

Accepted Answer

It prevents colonization by many microbes.

Question 5

Which cell type is most abundant among white blood cells and is specialized for engulfing and destroying microbes?

Accepted Answer

Neutrophils

Question 6

Natural killer (NK) cells play a crucial role in innate immunity by:

Accepted Answer

Triggering apoptosis in virus-infected and cancer cells.

Question 7

A B cell receptor binds to a specific, intact antigen. What is the structural difference between a B cell receptor and a secreted antibody?

Accepted Answer

Secreted antibodies lack the transmembrane region found in B cell receptors.

Question 8

T cell receptors recognize antigen fragments only when they are presented by cell-surface proteins. What are these proteins called?

Accepted Answer

Major histocompatibility complex (MHC) molecules

Question 9

Which class of MHC molecules is found on almost all nucleated cells and displays peptide antigens to cytotoxic T cells?

Accepted Answer

Class I MHC molecules

Question 10

During lymphocyte development, what process generates the diversity of antigen receptors?

Accepted Answer

Gene rearrangement

Question 11

What is the outcome when a lymphocyte’s antigen receptor binds to a self-antigen during maturation?

Accepted Answer

The lymphocyte is destroyed by apoptosis or rendered nonfunctional.

Question 12

Which equation best represents the possible combinations of B cell antigen receptors generated by gene rearrangement?

Accepted Answer

$$1.65 	imes 10^6$

Question 13

Clonal selection of B cells results in the formation of two types of cells. What are they?

Accepted Answer

Plasma cells and memory cells

Question 14

Which of the following best describes the humoral immune response?

Accepted Answer

Production of secreted antibodies by B cells

Question 15

Helper T cells are essential for both humoral and cell-mediated immunity. What is their primary function?

Accepted Answer

They secrete cytokines that stimulate other lymphocytes.

Question 16

Which antibody class is most abundant in blood and can cross the placenta to confer passive immunity?

Accepted Answer

IgG

Question 17

A newborn receives antibodies from its mother through breast milk. What type of immunity is this?

Accepted Answer

Passive immunity

Question 18

Transfusion of incompatible blood types can lead to destruction of transfused cells. What is the underlying cause?

Accepted Answer

The recipient’s immune system recognizes nonself antigens on red blood cells.

Question 19

A cytotoxic T cell recognizes an infected cell by binding to which combination of molecules?

Accepted Answer

Class I MHC molecule and antigen fragment

Question 20

Which of the following mechanisms is used by antibodies to dispose of antigens?

Accepted Answer

Activation of complement system leading to cell lysis

Chapter 43: The Immune System – Structure, Function, and Mechanisms

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