Question 1

The body's own cells do not trigger the alternative pathway of complement system activation. Why is this?

Accepted Answer

Host cell membranes contain molecules that bind regulatory proteins, such as factor H, that inactivate any C3b molecules that attach to the membrane. This prevents host cells from triggering the alternative pathway of complement system activation.

Question 2

Which of the following is mismatched regarding protection of the body from pathogens?

Accepted Answer

The stomach's primary defense against pathogens is its highly acidic conditions, which can kill or inhibit the growth of many microbes. While the stomach does have its own normal microbiota, these are adapted to survive in its acidic environment rather than serving as a primary defense mechanism. Thus, the pairing of "acid conditions and normal microbiota" as a defense mechanism is mismatched, as the acid conditions are the primary defense, not the microbiota.

Question 3

Smoking impairs the ciliated cells of the middle portion of the respiratory tract. Many analgesic drugs (painkillers) impair peristalsis (the churning motion of the digestive tract). The result of either of these activities leads to an increased risk of infection in their respective areas. Why?

Accepted Answer

The ciliated cells in the respiratory tract and the peristalsis in the digestive tract help to physically move pathogens out of the area, serving as a part of the physical barrier system. When these actions are impaired, bacteria and other pathogens have an easier time adhering to the tissues in the area and causing an infection.

Question 4

Fever allows the body to fight microbial invaders by which of the following mechanisms?

Accepted Answer

Fever raises the body's temperature, which can inhibit the growth of temperature-sensitive microbes, allowing the immune system more time to respond and eliminate the pathogens.

Question 5

Which of the following are enzymes found in neutrophil granules, saliva, and milk that react with hydrogen peroxide to form antimicrobial compounds?

Accepted Answer

Peroxidases are enzymes found in neutrophil granules, saliva, and milk that react with hydrogen peroxide to form antimicrobial compounds. Lactoferrins and transferrins are also found in these fluids, but they do not react with hydrogen peroxide to form antimicrobial compounds. Therefore, the best choice is A) peroxidases.

Question 6

Which of the following is NOT True of phagocytosis?

Accepted Answer

The correct statement is that within a phagolysosome, O₂ consumption increases (not decreases), which is part of the respiratory burst that allows enzymes to produce reactive oxygen species (ROS), which are toxic to the engulfed material.

Question 7

Please identify the INCORRECT definition regarding innate immunity.

Accepted Answer

The definition of innate lymphoid cells as having increased specificity in their mechanism of antigen recognition is incorrect. Innate lymphoid cells, including natural killer (NK) cells, are considered to have a limited specificity in their mechanism of antigen recognition.

Question 8

Which of the following is least likely to be detected by pattern recognition receptors?

Accepted Answer

Pattern recognition receptors are designed to recognize pathogen-associated molecular patterns (PAMPs) which are commonly found on microorganisms such as bacteria, viruses, and fungi. Enzymes involved in glycolysis are not PAMPs and therefore least likely to be detected by pattern recognition receptors.

Question 9

Syphilis, an STI, was once treated by intentionally infecting the patient with the parasite that causes malaria, a disease characterized by repeated bouts of fever, shaking, and chills. Why might this treatment cure syphilis?

Accepted Answer

The effect of driving up the body temperature for periods of time can shut down the temperature-sensitive replication of the bacterium that causes syphilis. This gives the immune system time to eliminate it properly.

Question 10

How do some pathogens prevent complement activation or avoid the effects of activated complement?

Accepted Answer

Some pathogens can prevent complement activation or avoid the effects of activated complement by producing C5a peptidase that destroys complement C5a, a chemoattractant that recruits phagocytes to the area of infection, and by hijacking the host's regulatory membrane proteins that inactivate C3b, preventing the triggering of the alternative activation pathway.

Question 11

Please select the correct sequence for the steps of phagocytosis:
1) Conditions in the phagosome change, increasing its antimicrobial activities.
2) The phagocytic cell binds microbial invaders and engulfs them, internalizing them in a phagosome.
3) Phagocytic cells are recruited to the site of an injury by chemoattractants. 
4) Within the phagolysosome, various factors work together to destroy an engulfed invader.
5) The phagosome fuses with enzyme-filled lysosomes, forming a phagolysosome.

Accepted Answer

The correct sequence for phagocytosis starts with the recruitment of phagocytic cells to the site of injury (3), followed by the binding and engulfment of microbial invaders (2). After engulfment, conditions within the phagosome change to increase antimicrobial activities (1). The phagosome then fuses with lysosomes to form a phagolysosome (5), where various factors work together to destroy the invader (4).

Question 12

Which of the following is a bacterial product?

Accepted Answer

Colicin is a bacterial product, which is a toxic protein produced by certain strains of E. coli. Lactoferrin and transferrin are proteins produced by mammals, defensin is produced by both mammals and plants, and mucus is a secretion produced by various tissues in animals.

Question 13

Which of the following is the correct sequence of events in the interferon response?
1) IFN induces synthesis of inactive antiviral proteins (iAVPs).
2) Virus enters host cell (cell 1) and replicates, producing long dsRNA.
3) Activated AVPs induce apoptosis of infected cell.
4) dsRNA induces synthesis and secretion of IFN to neighboring cells. 
5) Entry of virus into cell armed with iAVPs (cell 2) activates these proteins.

Accepted Answer

The correct sequence of events in the interferon response is as follows: 
1) Virus enters host cell (cell 1) and replicates, producing long dsRNA.
2) dsRNA induces synthesis and secretion of IFN to neighboring cells.
3) IFN induces synthesis of inactive antiviral proteins (iAVPs).
4) Entry of virus into cell armed with iAVPs (cell 2) activates these proteins.
5) Activated AVPs induce apoptosis of infected cell. 
Therefore, the correct sequence is 2-4-1-5-3, which corresponds to choice A.

Question 14

Which of the following would NOT trigger an inflammatory response?

Accepted Answer

Induction of antiviral protein synthesis by IFNs is not a trigger for the inflammatory response. Instead, it is part of the innate immune response that fights viral infections through the activation of infected cells to produce antiviral proteins. Inflammatory responses are triggered by tissue damage, infections or the presence of foreign substances in the body.

Question 15

Which of the following are lymphocytes?

Accepted Answer

Lymphocytes are a type of white blood cell that play a major role in the immune response. B cells and T cells are the two main types of lymphocytes and are responsible for specific immune responses against foreign pathogens. NK cells are also considered lymphocytes, but they are part of the innate immune system and do not have specific antigen recognition like B and T cells. Therefore, the correct answer is E.

Question 16

A cell infected by viruses may die due to the actions of interferons. The same result would occur WITHOUT interferon-any cell infected by a virus would die directly from the virus. Is there any apparent benefit to the host organism from the interferon action?

Accepted Answer

The interferon acts on a virally infected cell, it shuts down virus replication. Without interferon, the virus will eventually kill the cell, but only after it has replicated many times. IFNs may kill the host cell, but they will also prevent it from being used to replicate virus. Thus, the action of interferon has a benefit to the host organism by limiting viral replication.

Question 17

How are macrophages and neutrophils similar, and how are they different?

Accepted Answer

Macrophages and neutrophils are both phagocytic cells, meaning they engulf and digest foreign substances. However, macrophages are primarily tissue-resident cells while neutrophils circulate in the blood and migrate to sites of infection or inflammation.

Question 18

A physician is attempting new therapies for HIV patients who are suffering from an impaired immune response. He decides to try using a recombinant form of colony-stimulating factor cytokine (CSF). Why?

Accepted Answer

CSF is a colony-stimulating factor cytokine that can stimulate the production of new lymphocytes, which can help to maintain a normal immune response in HIV patients with an impaired immune system. While CSF can induce antiviral activities, it does not hyperstimulate macrophages, drive up production of lactoferrin and transferrin, or allow cells to communicate.

Question 19

Please identify the mismatched pair.

Accepted Answer

Peritoneal macrophages are found in the peritoneal cavity and play a role in the immune response to infections and foreign substances in the abdomen. They are not found in the meninges, which are the protective membranes around the brain and spinal cord.

Question 20

Please select the True statement regarding Toll-like receptors (TLRs).

Accepted Answer

C) TLRs allow cells to detect patterns associated with microbes, indicating that the innate immune responses involve some specificity (although not the specificity of adaptive immunity). This statement is true because TLRs (Toll-like receptors) are crucial in the innate immune system for recognizing molecular patterns common to pathogens, thus providing a form of specificity, albeit less precise than the adaptive immune system's recognition mechanisms.

Quiz 14: The Innate Immune Response