Question 1

Which component of Gram-negative lipopolysaccharide (LPS) is primarily responsible for its toxic effects in mammals?

Accepted Answer

Lipid A

Question 2

What is the main reason why LPS endotoxemia can lead to septic shock?

Accepted Answer

LPS induces excessive cytokine release, increasing capillary permeability and causing hypovolemia

Question 3

Which serum protein binds to LPS from lysed bacterial invaders and facilitates its recognition by phagocytes?

Accepted Answer

Lipopolysaccharide-binding protein (LBP)

Question 4

Which cytokines are secreted by monocytes in response to LPS binding to CD14 and TLR4?

Accepted Answer

TNF-α, IL-1, IL-6, IL-8

Question 5

Why has it been difficult to develop a vaccine against endotoxin?

Accepted Answer

Endotoxin is highly variable and not immunogenic enough for effective antibody production

Question 6

Which laboratory assay is commonly used to detect picogram quantities of LPS in medical preparations?

Accepted Answer

Amoebocyte lysate (LAL) assay

Question 7

Which of the following is a key difference between exotoxins and endotoxins?

Accepted Answer

Exotoxins are proteins often secreted, while endotoxins are lipid A components of LPS

Question 8

Which of the following best describes the mechanism of action of a typical A-B exotoxin?

Accepted Answer

The B subunit binds to the host cell receptor, allowing the A subunit to enter and exert toxic effects

Question 9

Which of the following is an example of a superantigen toxin and its effect?

Accepted Answer

TSST-1, which crosslinks TCR to MHC-II without antigen, causing massive T cell activation

Question 10

How do phospholipases produced by bacteria contribute to pathogenesis?

Accepted Answer

They remove the phospholipid head group, damaging host cell membranes and allowing bacteria to escape from phagosomes

Question 11

Which toxin is responsible for sloughing off the outer layer of skin in staphylococcal infections?

Accepted Answer

Exfoliative toxin

Question 12

What is the main pathological mechanism in acute glomerulonephritis following a streptococcal infection?

Accepted Answer

Immune complexes deposit in glomeruli, causing inflammation

Question 13

Which phenomenon describes antibodies against Streptococcal M protein cross-reacting with heart muscle, leading to tissue destruction?

Accepted Answer

Immune mimicry

Question 14

Which viral strategy allows evasion of the host immune system by preventing MHC-I antigen presentation?

Accepted Answer

Expression of MHC-I analogs (e.g., UL18 in cytomegalovirus)

Question 15

Why are Plasmodium parasites (malaria) not exposed to humoral or cellular immunity while inside red blood cells?

Accepted Answer

Red blood cells lack MHC and are not targeted by antibodies

Question 16

Which fungal enzyme is responsible for invading superficial skin layers, causing conditions like ringworm and athlete’s foot?

Accepted Answer

Keratinase

Question 17

A patient develops fever, malaise, a rash, and joint pain after a streptococcal infection. Which immune phenomenon is most likely responsible?

Accepted Answer

Immune mimicry leading to rheumatic fever

Question 18

Which of the following best explains how trypanosomes evade the host immune system?

Accepted Answer

Surface antigen variation

Question 19

A new LPS derivative binds to CD14 but not TLR4, allowing dendritic cell activation without excessive inflammation. What structural change in LPS is responsible for this effect?

Accepted Answer

Removal of one acyl chain

Question 20

Which equation best represents the relationship between LPS concentration and the response detected by the LAL assay?

Accepted Answer

$$Response = k 	imes [LPS]$$

Host-Pathogen Interactions: Toxins and Evasins

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