Immunology and immunological methods

37 Kerala PSC Lab Technician Gr II practice questions on Immunology and immunological methods, part of Biochemistry. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Easy

   The Mantoux (tuberculin) test is an example of which type of hypersensitivity?

   1. AType II (cytotoxic antibody)
   2. BType III (immune complex)
   3. CType I (immediate, IgE)
   4. DType IV (delayed, cell-mediated)

   Show answerHide answer

   Answer: D · Type IV (delayed, cell-mediated)

   Tuberculin PPD injected into the skin of a sensitised person is recognised by memory T cells, which release cytokines and recruit macrophages. The result is an indurated swelling that peaks at 48-72 hours, which is why the test is read then. No antibody is involved, so the reaction cannot be transferred with serum. Contact dermatitis and graft rejection are other type IV reactions.

   • A: Type II reactions are antibodies against cell-surface antigens, as in transfusion reactions.
   • B: Type III reactions are caused by immune complex deposits, as in serum sickness.
   • C: Type I reactions are IgE-mediated and appear within minutes.

2. Question 2 · Medium

   In a sandwich ELISA for an antigen, the colour that develops is:

   1. ADirectly proportional to the antigen
   2. BInversely proportional to the antigen
   3. CStrongest in the negative control
   4. DUnrelated to the antigen present

   Show answerHide answer

   Answer: A · Directly proportional to the antigen

   In a sandwich ELISA, antigen in the sample is captured between an antibody fixed to the well and an enzyme-labelled detecting antibody. The more antigen there is, the more enzyme stays bound after washing and the stronger the colour from the substrate. In a competitive ELISA, patient antigen competes with labelled antigen, so the colour falls as the antigen rises. TSH and ferritin assays commonly use the sandwich format.

   • B: Inverse proportion describes a competitive assay.
   • C: The negative control should give little or no colour.
   • D: In a valid assay the colour depends on the amount of antigen captured.

3. Question 3 · Easy

   Who first developed radioimmunoassay?

   1. AYalow and Berson
   2. BKöhler and Milstein
   3. CEngvall and Perlmann
   4. DCoons and Kaplan

   Show answerHide answer

   Answer: A · Yalow and Berson

   Rosalyn Yalow and Solomon Berson described radioimmunoassay around 1960 while measuring insulin in plasma, and Yalow later received the Nobel Prize for it. The method uses a radioactive tracer, such as iodine-125, that competes with the patient's antigen for antibody. Engvall and Perlmann introduced ELISA, Köhler and Milstein made monoclonal antibodies, and Coons and Kaplan developed fluorescent antibody staining. RIA made it possible to measure hormones present in very small amounts.

   • B: Köhler and Milstein made the first monoclonal antibodies.
   • C: Engvall and Perlmann introduced ELISA.
   • D: Coons and Kaplan developed fluorescent antibody staining.

4. Question 4 · Hard

   Minutes after the vascular clamps are released, a transplanted kidney turns blue and stops working. Donor and recipient are ABO identical; the recipient has had three pregnancies. Which pre-transplant test would have predicted this?

   1. ADirect antiglobulin test on the recipient
   2. BMixed lymphocyte culture of donor and recipient
   3. CCrossmatch of recipient serum with donor lymphocytes
   4. DRepeat ABO grouping of donor and recipient

   Show answerHide answer

   Answer: C · Crossmatch of recipient serum with donor lymphocytes

   Rejection within minutes is hyperacute rejection, caused by preformed antibodies that bind the graft's blood vessels and activate complement. With ABO-identical donor and recipient, the likely antibodies are anti-HLA antibodies formed during her pregnancies. A complement-dependent cytotoxicity (or flow cytometry) crossmatch of recipient serum against donor lymphocytes detects them, and a positive crossmatch is a bar to transplant. A mixed lymphocyte culture measures T-cell reactivity, which drives later acute rejection.

   • A: The DAT detects antibody on the recipient's red cells, not anti-HLA antibodies.
   • B: Mixed lymphocyte culture tests T-cell reactivity, which causes acute rejection over days to weeks.
   • D: ABO is stated to be identical, so regrouping would not explain the reaction.

5. Question 5 · Medium

   Serum immunoelectrophoresis from a patient with multiple myeloma typically shows:

   1. AA thick bowed arc with one light-chain antiserum
   2. BArcs identical to the normal control serum
   3. CFaint thin arcs for every immunoglobulin class
   4. DThick arcs with both kappa and lambda antisera

   Show answerHide answer

   Answer: A · A thick bowed arc with one light-chain antiserum

   In immunoelectrophoresis, serum proteins are first separated by electrophoresis and then allowed to diffuse against antisera placed in a trough, forming precipitin arcs. A monoclonal protein from one plasma cell clone has a single heavy chain and a single light chain type, so it forms a dense, localised, bowed arc with one heavy-chain antiserum and with either anti-kappa or anti-lambda, not both. A polyclonal rise, as in chronic infection or liver disease, thickens the arcs with both light chains. Immunofixation has largely replaced immunoelectrophoresis but works on the same principle.

   • B: A normal pattern lacks the localised abnormal arc of a myeloma protein.
   • C: Faint arcs for all classes indicate hypogammaglobulinemia.
   • D: Thick arcs with both kappa and lambda indicate a polyclonal increase.

6. Question 6 · Easy

   What activates the classical pathway of complement?

   1. AAntigen-antibody complexes
   2. BMicrobial surfaces directly
   3. CHistamine from mast cells
   4. DMannose-binding lectin

   Answer and explanation in LearnFree account

7. Question 7 · Hard

   A 26-year-old woman has a facial rash, joint pains and 2+ proteinuria. ANA by indirect immunofluorescence on HEp-2 cells is positive, homogeneous pattern, titre 1:640. Which test best supports the likely diagnosis?

   1. AAnti-mitochondrial antibody
   2. BRheumatoid factor
   3. CAnti-double-stranded DNA antibody
   4. DAnti-centromere antibody

   Answer and explanation in LearnFree account

8. Question 8 · Medium

   A 2-year-old boy has had repeated bacterial chest infections since 6 months of age. IgG, IgA and IgM are very low, B cells are absent and T cells are normal. What is the most likely diagnosis?

   1. ASevere combined immunodeficiency
   2. BSelective IgA deficiency
   3. CX-linked agammaglobulinemia
   4. DDiGeorge syndrome

   Answer and explanation in LearnFree account

9. Question 9 · Easy

   Which immunoglobulin predominates in colostrum, saliva and tears?

   1. AMembrane IgD
   2. BPentameric IgM
   3. CSerum IgG
   4. DSecretory IgA

   Answer and explanation in LearnFree account

10. Question 10 · Medium

    In a competitive radioimmunoassay, what happens to the bound radioactivity as the patient's antigen concentration rises?

    1. AIt rises, then falls
    2. BIt falls
    3. CIt stays the same
    4. DIt rises

    Answer and explanation in LearnFree account

11. Question 11 · Medium

    In the complement fixation test, the indicator system shows lysis of the sheep red cells. What does this mean?

    1. AThe test is negative
    2. BThe test is positive
    3. CThe complement was inactive
    4. DThe antigen was missing

    Answer and explanation in LearnFree account

12. Question 12 · Easy

    All of the following statements about immunoglobulin M are true EXCEPT:

    1. AIt activates complement strongly
    2. BIt is a pentamer with a J chain
    3. CIt appears first in a primary response
    4. DIt crosses the placenta

    Answer and explanation in LearnFree account

13. Question 13 · Easy

    Immunity produced by an injection of tetanus toxoid is:

    1. ANaturally acquired passive immunity
    2. BNaturally acquired active immunity
    3. CArtificially acquired passive immunity
    4. DArtificially acquired active immunity

    Answer and explanation in LearnFree account

14. Question 14 · Medium

    Which lymphocytes can kill tumour cells without prior sensitisation and without needing MHC class I on the target?

    1. ACytotoxic T cells
    2. BHelper T cells
    3. CNatural killer cells
    4. DPlasma cells

    Answer and explanation in LearnFree account

15. Question 15 · Easy

    Which of these is an enzyme label used in ELISA?

    1. AHorseradish peroxidase
    2. BAcridinium ester
    3. CIodine-125
    4. DFluorescein isothiocyanate

    Answer and explanation in LearnFree account

16. Question 16 · Easy

    The primary (central) lymphoid organs in humans are the:

    1. ASpleen and lymph nodes
    2. BLiver and spleen
    3. CTonsils and Peyer's patches
    4. DBone marrow and thymus

    Answer and explanation in LearnFree account

17. Question 17 · Hard

    A man with a large liver mass has serum AFP 380 ng/mL by a one-step sandwich immunoassay. At 1:100 dilution the same sample reads 95 ng/mL, that is 9,500 ng/mL after correction. What explains the low undiluted result?

    1. ACross-reaction with albumin
    2. BHigh-dose hook effect
    3. CHeterophile antibody interference
    4. DHemolysis of the sample

    Answer and explanation in LearnFree account

18. Question 18 · Medium

    In counter-current immunoelectrophoresis at pH 8.6, antigen and antibody move towards each other. Why does the antibody move towards the cathode?

    1. AIgG is too large to enter the gel
    2. BElectroendosmosis carries the IgG along
    3. CThe antigen pulls the antibody along
    4. DIgG is strongly positively charged

    Answer and explanation in LearnFree account

19. Question 19 · Medium

    Agglutination tests differ from precipitation tests in that, in agglutination, the antigen is:

    1. AParticulate, on cells or particles
    2. BPresent only in very large excess
    3. CAlways a small hapten molecule
    4. DSoluble in the patient's serum

    Answer and explanation in LearnFree account

20. Question 20 · Hard

    In an HBsAg ELISA plate, the negative controls and most patient wells develop strong colour, while the positive control reads as expected. The plate washer's nozzles were found partly blocked. What is the most likely cause of the colour?

    1. AHemolysed patient samples
    2. BExpired positive control
    3. CUnbound conjugate left by poor washing
    4. DToo short substrate incubation

    Answer and explanation in LearnFree account

21. Question 21 · Medium

    Serum CA-125 is mainly used to monitor treatment and recurrence of which cancer?

    1. AColorectal carcinoma
    2. BHepatocellular carcinoma
    3. CProstatic carcinoma
    4. DOvarian carcinoma

    Answer and explanation in LearnFree account

22. Question 22 · Medium

    Cellular blood components for a bone marrow transplant recipient are irradiated mainly to prevent:

    1. ATransfusion-associated graft-versus-host disease
    2. BTransmission of hepatitis B virus
    3. CFebrile non-haemolytic transfusion reaction
    4. DAcute haemolytic transfusion reaction

    Answer and explanation in LearnFree account

23. Question 23 · Easy

    Serum sickness after an injection of horse antiserum is an example of which type of hypersensitivity?

    1. AType IV, delayed
    2. BType III, immune complex
    3. CType II, cytotoxic
    4. DType I, anaphylactic

    Answer and explanation in LearnFree account

24. Question 24 · Medium

    In Ouchterlony double diffusion, the precipitin lines from two adjacent antigen wells fuse into a smooth continuous arc. This means the antigens are:

    1. AIdentical
    2. BAbsent
    3. CUnrelated
    4. DPartly related

    Answer and explanation in LearnFree account

25. Question 25 · Easy

    Maternal anti-D can destroy the red cells of an Rh-positive fetus because, being IgG, it is able to:

    1. APass into breast milk
    2. BActivate mast cells
    3. CCross the placenta
    4. DForm large pentamers

    Answer and explanation in LearnFree account