Unit 3: Antigen - antibody interactions - Practice Quiz

1 The affinity of an antibody refers to which of the following?

2 The term avidity best describes which concept?

3 Which antibody class generally has the highest avidity due to its multiple binding sites?

4 Cross-reactivity occurs when an antibody binds to which of the following?

5 Which classic example demonstrates cross-reactivity in blood group serology?

6 A precipitation reaction typically involves an antibody reacting with which type of antigen?

7 In a precipitation curve, maximum precipitate forms in which zone?

8 Which technique uses precipitation in a gel where both antigen and antibody diffuse toward each other?

9 Agglutination reactions involve antibodies reacting with which type of antigen?

10 The clumping of red blood cells by antibodies is specifically called what?

11 The prozone phenomenon in agglutination is caused by which condition?

12 In a radioimmunoassay (RIA), what is used as the label to detect antigen-antibody binding?

13 Radioimmunoassay is particularly valued for which of the following characteristics?

14 In an ELISA, the label attached to the antibody is typically which of the following?

15 In a sandwich ELISA, the antigen is captured between which two components?

16 A positive ELISA result is most commonly detected as which observable change?

17 Immunofluorescence uses antibodies labeled with what type of molecule?

18 Which fluorescent dye is commonly used to label antibodies and emits green light?

19 In direct immunofluorescence, the fluorochrome is attached to which antibody?

20 The Western blot (immunoblot) technique is used to detect which type of molecule?

21 Antibody A binds an epitope with an affinity constant , while Antibody B binds the same epitope with . What can be concluded?

22 Why does IgM often show high avidity despite its individual binding sites having relatively low affinity?

23 A patient recovering from a streptococcal infection develops antibodies that also react with heart tissue. This phenomenon is best explained by:

24 In an ELISA, an antiserum raised against Antigen X also gives a positive signal with Antigen Y. Which is the most likely explanation?

25 In a precipitation reaction, maximum precipitate forms at the zone of equivalence. What happens in the zone of antibody excess?

26 In radial immunodiffusion, the diameter of the precipitin ring is related to antigen concentration in what way?

27 In the Ouchterlony double diffusion test, two adjacent antigens form precipitin lines that fuse smoothly into a continuous arc. This indicates the antigens are:

28 The prozone phenomenon in an agglutination test results in a false-negative result because:

29 Why is the Coombs (antiglobulin) test needed to detect certain anti-Rh antibodies on red blood cells?

30 In passive (indirect) hemagglutination, soluble antigen is first adsorbed onto red blood cells. What is the purpose of this step?

31 In a competitive radioimmunoassay (RIA), how does the measured radioactive signal relate to the amount of unlabeled antigen in the sample?

32 Which property makes RIA particularly useful for measuring hormones present at very low concentrations?

33 In a sandwich ELISA, the antigen is captured between two antibodies. What is a key requirement of the antigen for this format to work?

34 In an indirect ELISA measuring antibody in a patient's serum, what does the enzyme-conjugated secondary antibody bind to?

35 If the substrate is added to an ELISA well but no color develops in a sample expected to be positive, which is the most likely technical cause?

36 In indirect immunofluorescence, why can a single fluorochrome-labeled secondary antibody be used with many different primary antibodies?

37 A researcher wants to simultaneously visualize two different proteins in the same cell using immunofluorescence. What is the essential requirement?

38 In a Western blot, proteins are separated by SDS-PAGE before transfer to a membrane. What property primarily determines this separation?

39 During a Western blot, why is the membrane incubated with a blocking agent such as non-fat milk before adding the primary antibody?

40 In immunohistochemistry (IHC), what is the main advantage compared to immunofluorescence for routine diagnostic tissue examination?

41 The intrinsic affinity of an antibody for a monovalent hapten is described by the association constant . If at equilibrium the concentration of free hapten equals the reciprocal of , what fraction of antibody binding sites are occupied?

42 Two antibodies, X and Y, bind the same multivalent antigen. Antibody X has higher intrinsic affinity per site, but antibody Y shows higher functional avidity in cell-binding assays. Which explanation is most consistent with these observations?

43 An antiserum raised against antigen A reacts with antigen B at 20% of its titer against A. Scatchard-type analysis shows the anti-A antibodies bind B with a that is 5-fold lower than for A. Which interpretation is most accurate?

44 In the ABO blood group system, anti-A and anti-B isohemagglutinins arise without prior transfusion. What best explains their origin through cross-reactivity?

45 In a quantitative precipitin curve, increasing antigen beyond the equivalence zone causes the amount of precipitate to decrease. What is the mechanistic reason for this prozone-analogous 'postzone' behavior?

46 In double immunodiffusion (Ouchterlony), two adjacent antigen wells are tested against a central antiserum. The precipitin lines cross each other forming an X. What does this pattern indicate?

47 In radial immunodiffusion (Mancini method) at endpoint, the relationship between the diameter of the precipitin ring and antigen concentration is best described as:

48 A serum with a very high antibody titer gives a negative agglutination result at low dilution but strong agglutination at higher dilutions. What phenomenon explains the false negative at low dilution?

49 The antiglobulin (Coombs) test is required to detect certain anti-Rh antibodies in hemagglutination assays. Why do these antibodies fail to directly agglutinate red cells?

50 In a competitive RIA, patient sample analyte competes with a fixed amount of radiolabeled analyte for limited antibody. As the concentration of unlabeled analyte in the sample increases, the bound radioactivity signal:

51 A researcher wishes to improve the lower limit of detection of a competitive RIA. Which change would most effectively lower the detection limit?

52 In a sandwich ELISA at very high analyte concentrations the measured signal paradoxically falls, giving a hook effect. What is the underlying cause?

53 A competitive ELISA and a sandwich ELISA are compared for measuring a small hapten (~400 Da). Which format is appropriate and why?

54 In an indirect ELISA measuring anti-viral IgG, background signal is unacceptably high in negative controls. Which single change most specifically reduces nonspecific binding without affecting true signal?

55 In indirect immunofluorescence, a primary rabbit antibody is detected with a fluorophore-labeled anti-rabbit secondary. Compared with direct immunofluorescence, the indirect method gives stronger signal primarily because:

56 When performing dual-color immunofluorescence with FITC (green) and a red fluorophore, bleed-through causes the FITC channel to show false red-region signal. Which correction is most appropriate?

57 In a Western blot, a protein known to be 50 kDa migrates as a band at ~100 kDa under non-reducing conditions but at 50 kDa with reducing SDS-PAGE. The most likely explanation is:

58 A Western blot shows the target band plus several unexpected higher- and lower-molecular-weight bands. Which action best distinguishes genuine cross-reactivity of the antibody from proteolytic degradation of the target?

59 In formalin-fixed paraffin-embedded tissue, an antibody that works on frozen sections gives no staining. Which pretreatment most directly addresses the likely cause?

60 In an IHC assay of a tissue rich in endogenous peroxidase using an HRP-based detection system, strong staining appears even in the no-primary-antibody control. The most appropriate corrective step is: