Block 9 Innate Def Compliment & Antibody MCQ

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Questions and Answers
  • 1. 

    A 70-year-old man is admitted to the hospital for recurrent lung infections with Streptococcus pneumonae. He has a history of chronic alcoholism and a 100 pack year smoking history. Extensive laboratory testing reveals that he cannot activate the alternate pathway of complement. A lung biopsy reveals numerous bacteria, but few leukocytes in the lung. Which of the following mediators is Most Likely deficient?

    • A.

      C3b

    • B.

      C4a

    • C.

      C5a

    • D.

      C6

    • E.

      Membrane attack complex

    Correct Answer
    C. C5a
    Explanation
    The patient's inability to activate the alternate pathway of complement suggests a deficiency in one of the complement components involved in this pathway. C5a is a potent chemotactic factor that attracts neutrophils to the site of infection. In this case, the patient's lung biopsy reveals numerous bacteria but few leukocytes, indicating a deficiency in C5a. This deficiency would impair the recruitment of neutrophils to the site of infection, leading to recurrent lung infections.

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  • 2. 

    The complement cascade can be activated in a number of ways. Cobra venom factor (CVF) is one of these ways. Which pathway is activated by CVF?

    • A.

      The lectin pathway

    • B.

      The alternative pathway

    • C.

      The classical pathway

    • D.

      Both the lectin and the classical pathway

    Correct Answer
    B. The alternative pathway
    Explanation
    CVF activates the alternative pathway of the complement cascade. The alternative pathway is one of the three pathways of the complement system, along with the lectin and classical pathways. CVF specifically triggers the alternative pathway, leading to the activation of complement proteins and the subsequent immune response.

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  • 3. 

    A 23 year old female patient presents with a malar rash, joint pains and general malaise. Laboratory tests indicated the presence of anti-Sm and anti-ds DNA antibodies. If you were to measure the patients complement C2 and C4 levels, what might you expect?

    • A.

      C4 and C2 would be lower than the normal range

    • B.

      C2 and C4 would be higher than the normal range

    • C.

      C2 would be higher and C4 lower than the normal range

    • D.

      C2 would be lower and C4 higher than the normal range

    Correct Answer
    A. C4 and C2 would be lower than the normal range
    Explanation
    The presence of anti-Sm and anti-ds DNA antibodies in a patient with a malar rash, joint pains, and general malaise suggests a diagnosis of systemic lupus erythematosus (SLE). In SLE, the complement system is often activated, leading to consumption of complement proteins such as C2 and C4. Therefore, it is expected that C2 and C4 levels would be lower than the normal range in this patient.

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  • 4. 

    In complement activation, the mannan binding lectin (MBL) pathway is characterized by which of the following?

    • A.

      MBL is synthesized by the liver when stimulated by IL-2

    • B.

      MBL acts on C4 to produce C4b and C4a

    • C.

      MBL acts on C3 to produce C3b and C3a

    • D.

      MBL is important in controlling infection after the classical pathway is activated

    Correct Answer
    B. MBL acts on C4 to produce C4b and C4a
    Explanation
    The correct answer is MBL acts on C4 to produce C4b and C4a. The MBL pathway of complement activation involves MBL binding to microbial surfaces and initiating the lectin pathway. MBL forms complexes with MBL-associated serine proteases (MASPs), which then cleave C4 into C4a and C4b. This leads to the formation of the C3 convertase and subsequent activation of the complement cascade. MBL is not synthesized by the liver when stimulated by IL-2, and it does not directly act on C3 to produce C3b and C3a. Additionally, MBL is important in initiating complement activation, not in controlling infection after the classical pathway is activated.

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  • 5. 

    Innate defenses, Complement, Antigen and antibody structure and function Toll-like receptors (TLR) are important activators of the innate immune system. Which of the following microbial substances activates TLR-4?

    • A.

      Peptidoglycan

    • B.

      Lipopolysaccaride

    • C.

      Double stranded RNA

    • D.

      Bacterial flagella

    • E.

      Single stranded RNA

    Correct Answer
    B. Lipopolysaccaride
    Explanation
    TLR-2 binds to peptidoglycan of Gram-positive bacteria, likeStaphylococci and Streptococci;
    TLR-3 binds to dsRNA;
    TLR-4 binds to LPS (endotoxin) of Gram-negative bacteria;
    TLR-5 binds to flagellin of motile bacteria.

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  • 6. 

    Patients with Leukocyte adhesion deficiency syndrome (LAD) are unable to produce the beta chain of the complement receptor 3 (CR3) heterodimer. Which of the following functions may be deficient in LAD patients?

    • A.

      Lysis of bacteria

    • B.

      Opsonization of bacteria

    • C.

      Leukocyte chemotaxis

    • D.

      Neutrophil diapedesis

    • E.

      Macrophage activation

    Correct Answer
    B. Opsonization of bacteria
    Explanation
    LAD patients are unable to produce the beta chain of the complement receptor 3 (CR3) heterodimer. Opsonization is the process of marking bacteria for destruction by immune cells, and it relies on the interaction between CR3 and complement proteins. Since LAD patients lack the beta chain of CR3, their ability to opsonize bacteria is likely to be deficient. This means that their immune system may have difficulty recognizing and destroying bacteria, making them more susceptible to infections.

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  • 7. 

    The activity of complement is dependent on the sequential activation of its components in a cascading fashion. Which of the complement activation pathways would be most severely affected by a defect in the synthesis of Factor D?

    • A.

      The alternate pathway

    • B.

      The classical pathway

    • C.

      The lectin pathway

    • D.

      None of the pathway would be affected

    Correct Answer
    A. The alternate pathway
    Explanation
    A defect in the synthesis of Factor D would most severely affect the alternate pathway of complement activation. Factor D is a crucial component of the alternate pathway, as it cleaves Factor B to generate the active fragment, Bb. This leads to the formation of the C3 convertase, which is essential for the amplification and activation of the complement cascade. Without Factor D, the alternate pathway would be unable to proceed, resulting in a significant impairment of complement activity.

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  • 8. 

    Which of the following immunoglobulin regions/domains determine the affinity, specificity and idiotype of the molecule?

    • A.

      The light chain hypervariable and constant domains

    • B.

      The light and heavy chain hypervariable and constant domains.

    • C.

      The light and heavy chain hypervariable domains

    • D.

      The light chain hypervariable domains

    • E.

      The light and heavy chain framework domains

    Correct Answer
    C. The light and heavy chain hypervariable domains
    Explanation
    The light and heavy chain hypervariable domains determine the affinity, specificity, and idiotype of the immunoglobulin molecule. These domains contain highly variable amino acid sequences that contribute to the binding of antigens with high affinity and specificity. The hypervariable domains are responsible for the unique antigen-binding properties of each individual immunoglobulin molecule, giving rise to the idiotype. The constant domains, on the other hand, provide structural stability to the molecule. Therefore, the correct answer is the light and heavy chain hypervariable domains.

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  • 9. 

    V(D) J recombination events take place in the following cells

    • A.

      Natural killer cells, B cells & neutrophils

    • B.

      Eosinophils, T cells & B cells

    • C.

      B cells, dendritic cells & T cells

    • D.

      Plasma cells, mast cells and, B cells

    • E.

      CD4+ T cells, CD8+ T cells & B cells

    Correct Answer
    E. CD4+ T cells, CD8+ T cells & B cells
  • 10. 

    A single patient that produces IgG1 to differing epitopes will have which of the following?

    • A.

      Same isotype, same allotype, same idiotype

    • B.

      Same isotype, different allotype and different idiotype

    • C.

      Same isotype, different allotype, same idiotype

    • D.

      Different isotype, different allotype, different idiotype

    • E.

      Same isotype, same allotype, different idiotype

    Correct Answer
    E. Same isotype, same allotype, different idiotype
    Explanation
    A single patient that produces IgG1 to differing epitopes will have the same isotype (IgG1), indicating that the antibodies belong to the same class of immunoglobulins. They will also have the same allotype, which refers to the genetic variations within the same isotype. However, they will have different idiotype, which refers to the unique antigen-binding sites on the antibodies. This means that while the antibodies have the same overall structure and genetic background, they recognize different epitopes or antigens.

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  • 11. 

    In 1972 Rodney Porter won the Nobel Prize for demonstrating the structure of antibodies. He digested IgG using papain to produce what?

    • A.

      One F(ab')2 plus some small fragments

    • B.

      2 Fab plus one Fc

    • C.

      2 Fc plus one Fab

    • D.

      One F(ab')2 plus one Fc

    Correct Answer
    B. 2 Fab plus one Fc
    Explanation
    Rodney Porter won the Nobel Prize in 1972 for his work on the structure of antibodies. In his research, he used papain to digest IgG, which resulted in the production of 2 Fab fragments and one Fc fragment. The Fab fragments are responsible for binding to antigens, while the Fc fragment is involved in various immune functions. Therefore, the correct answer is 2 Fab plus one Fc.

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  • 12. 

    IgM differs from IgG in a number of ways, but which of the following differences between IgG and IgM would you agree with?

    • A.

      IgM is almost always low affinity for antigen, while IgG is usually high affinity for antigen.

    • B.

      IgM, but not IgG can bind to soluble antigens

    • C.

      Certain subtypes of IgG, can activate complement, but IgM can almost never activate complement by the classical pathway.

    • D.

      Both IgM and IgG are produced subsequent to somatic hypermutation of BCR genes. innate defenses, Complement, Antigen and antibody structure and function

    Correct Answer
    A. IgM is almost always low affinity for antigen, while IgG is usually high affinity for antigen.
    Explanation
    IgM is almost always low affinity for antigen, while IgG is usually high affinity for antigen. This means that IgM antibodies have a lower binding strength to antigens compared to IgG antibodies. IgM antibodies are typically the first antibodies produced during an immune response and have a pentameric structure, allowing them to efficiently bind to multiple antigens simultaneously. On the other hand, IgG antibodies are produced later in the immune response and have a monomeric structure, which allows them to have a higher affinity for specific antigens. This difference in affinity allows IgM to quickly recognize and bind to a wide range of antigens, while IgG provides a more specific and stronger immune response.

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  • 13. 

    Antibodies of different classes, including IgM, IgG, IgA, and IgE, arise after varying kinds of antigenic stimulation. In which of the following situations would particular antibody responses be expected?

    • A.

      Antigens such as polysaccharides give rise to T cell-dependent responses resuting in mostly IgG

    • B.

      Antigens such as proteins give rise to T cell-independent responses resulting in mostly IgM

    • C.

      IgM produced after exposure to a carbohydrate antigen will have relatively low affinity for its antigen

    • D.

      When antigen is presented at mucosal surfaces, IgE is likely to be the main antibody secreted at the surface

    Correct Answer
    C. IgM produced after exposure to a carbohydrate antigen will have relatively low affinity for its antigen
    Explanation
    When exposed to a carbohydrate antigen, IgM antibodies are produced with relatively low affinity for the antigen. This is because carbohydrate antigens typically do not have well-defined epitopes, making it difficult for antibodies to bind tightly to them. As a result, the IgM antibodies produced in response to a carbohydrate antigen will have lower affinity compared to antibodies produced in response to other antigens such as proteins.

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