Exam Prep
Immunoglobulins, complement, hypersensitivity, immunoassays, autoimmunity, infectious serology and transplant immunology.
Independent practice questions written by Labologics. Not affiliated with DHA, DOH (formerly HAAD), SCFHS, Prometric or any exam body. Not recalled exam questions.
Which immunoglobulin is the most abundant in serum?
Answer: A — IgG
IgG makes up about 75-80% of serum immunoglobulin and has the longest half-life (about 21-23 days).
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which immunoglobulin crosses the placenta?
Answer: B — IgG
IgG is actively transported across the placenta by the neonatal Fc receptor (FcRn), giving the newborn passive immunity for the first months.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which immunoglobulin is produced first in a primary immune response?
Answer: C — IgM
IgM appears first and indicates recent or acute infection. IgG follows and indicates later, past infection or immunity.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Secretory IgA in tears, saliva and mucus exists mainly as a:
Answer: D — Dimer joined by a J chain and secretory component
Secretory IgA protects mucosal surfaces. IgM is a pentamer (with a J chain) and has 10 antigen-binding sites.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Why is IgM very efficient at agglutination and complement activation?
Answer: A — It is a pentamer with 10 antigen-binding sites
Its many binding sites can bridge red cells and activate the classical pathway strongly. ABO antibodies are mainly IgM.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which immunoglobulin binds to mast cells and basophils and mediates type I hypersensitivity?
Answer: B — IgE
IgE has the lowest serum concentration. It also rises in helminth (parasitic) infections.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which part of an antibody binds the antigen?
Answer: C — Fab region
The Fab (fragment antigen-binding) carries the variable regions. The Fc (fragment crystallizable) binds cell Fc receptors and complement.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
A basic immunoglobulin monomer is made of:
Answer: D — Two heavy and two light chains
Two identical heavy chains and two identical light chains (kappa or lambda), joined by disulfide bonds.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which is NOT a main biological function of antibodies?
Answer: A — Direct killing of virus-infected cells with perforin
Cytotoxic T cells and NK cells kill infected cells using perforin and granzymes. Antibodies can also mediate ADCC via NK cells.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
The overall strength of binding between a multivalent antibody and a multivalent antigen is called:
Answer: B — Avidity
Affinity is the strength of one binding site with one epitope. Avidity is the combined strength of all binding sites.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which cells secrete antibodies?
Answer: C — Plasma cells
Plasma cells are terminally differentiated B cells.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
A hybridoma used to produce monoclonal antibodies is made by fusing:
Answer: D — An antibody-producing B cell and a myeloma cell
The B cell supplies the specific antibody; the myeloma cell makes the hybrid immortal.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Where do T lymphocytes mature?
Answer: A — Thymus
T cells mature in the thymus, where self-reactive cells are removed (central tolerance). B cells mature in the bone marrow.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
How does the adaptive immune system learn to tolerate self-antigens?
Answer: B — Developing T cells that react strongly to self are deleted in the thymus
Negative selection in the thymus (central tolerance) removes most self-reactive T cells; peripheral mechanisms such as regulatory T cells add further control.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
CD4 is the marker of:
Answer: C — Helper T cells
CD8 marks cytotoxic T cells, CD19/CD20 B cells, and CD16/CD56 NK cells. HIV infects CD4 cells.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which cells kill virus-infected and tumor cells without prior sensitization and mediate ADCC?
Answer: D — Natural killer (NK) cells
NK cells are innate lymphocytes. Through CD16 (an Fc receptor) they kill antibody-coated cells (ADCC).
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Langerhans cells in the epidermis are:
Answer: A — Dendritic (antigen-presenting) cells
Dendritic cells, macrophages and B cells are professional antigen-presenting cells expressing HLA class II.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
A child with pinworm infection is most likely to have an increase in:
Answer: B — Eosinophils
Eosinophils rise in helminth infections and allergic disease.
Reference: Turgeon: Immunology & Serology in Laboratory Medicine
The white cell present in the lowest numbers in normal blood is the:
Answer: C — Basophil
Basophils are usually below 1% of white cells. With mast cells, they release histamine in allergic reactions.
Reference: Turgeon: Immunology & Serology in Laboratory Medicine
Lymphoid tissue in the gut, bronchi and nasal mucosa is collectively called:
Answer: D — MALT
Mucosa-associated lymphoid tissue (MALT) includes GALT (gut), BALT (bronchus) and NALT (nasal).
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which molecules are expressed on almost all nucleated cells and present antigen to CD8 T cells?
Answer: A — HLA class I
HLA class II is expressed mainly on antigen-presenting cells (B cells, macrophages, dendritic cells) and activated T cells, and presents antigen to CD4 T cells.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which T helper cytokine profile drives macrophage activation against intracellular pathogens such as M. tuberculosis?
Answer: B — Th1 (IFN-gamma, IL-2)
Th1 responses activate macrophages and cell-mediated immunity. Th2 responses support IgE, eosinophils and antiparasitic immunity.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
The complement component present in the highest concentration in serum is:
Answer: C — C3
C3 is central to all three pathways (classical, lectin and alternative).
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
The membrane attack complex (MAC) is formed by:
Answer: D — C5b, C6, C7, C8 and C9
MAC forms pores in cell membranes and causes lysis. Deficiency of terminal components predisposes to Neisseria infections.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which factor is specific to the alternative complement pathway?
Answer: A — Factor B
The alternative pathway uses factors B, D and properdin. C1q and C4 belong to the classical pathway; MBL starts the lectin pathway.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Serum is heated to 56 C for 30 minutes before some serological tests in order to:
Answer: B — Inactivate complement
Complement is heat-labile. Samples for complement assays must be fresh, or frozen promptly, because complement activity is lost on standing.
Reference: Turgeon: Immunology & Serology in Laboratory Medicine
In a complement fixation test, how is a POSITIVE result seen?
Answer: C — No hemolysis of the indicator red cells
If patient antibody binds antigen, complement is used up (fixed), so none is left to lyse the sensitized indicator cells. Hemolysis means a negative result.
Reference: Turgeon: Immunology & Serology in Laboratory Medicine
A man develops tongue swelling and difficulty breathing minutes after eating peanuts. This is a:
Answer: D — Type I (IgE-mediated) hypersensitivity
Allergen cross-links IgE on mast cells and basophils, releasing histamine and other mediators within minutes. Severe cases are anaphylaxis.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Hemolytic transfusion reactions and hemolytic disease of the newborn are examples of:
Answer: A — Type II (antibody against cell-surface antigen)
In type II reactions, IgG or IgM binds antigens on cells, leading to complement-mediated lysis or phagocytosis.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
A painful local swelling hours after a repeated tetanus booster (an Arthus reaction) is an example of:
Answer: B — Type III (immune complex) hypersensitivity
Antigen-antibody complexes deposit locally, activate complement and attract neutrophils. Serum sickness and SLE nephritis are systemic type III examples.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
A positive tuberculin (Mantoux) skin test read at 48-72 hours is an example of:
Answer: C — Type IV delayed hypersensitivity
Type IV reactions are mediated by T cells (not antibodies) and appear after 24-72 hours. Contact dermatitis is another example.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
A patient with IgA deficiency has anaphylaxis during a plasma transfusion. The most likely cause is:
Answer: D — Anti-IgA antibodies in the patient reacting with IgA in the donor plasma
Some IgA-deficient patients make anti-IgA. They need IgA-deficient donor products or washed red cells.
Reference: Turgeon: Immunology & Serology in Laboratory Medicine
A false-negative result caused by ANTIBODY excess in a precipitation or agglutination test is called:
Answer: A — Prozone
In prozone, too much antibody prevents lattice formation. Diluting the serum restores the reaction. Postzone is antigen excess.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
In an ELISA, the color develops when:
Answer: B — The enzyme label acts on its substrate
The substrate is added last. The enzyme (for example, horseradish peroxidase) converts it to a colored product, and the color is measured by a plate reader.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
In an indirect ELISA, the plate is coated with antigen. This format is used to detect:
Answer: C — Antibody in the patient's sample
Patient antibody binds the antigen, then an enzyme-labelled anti-human immunoglobulin detects it.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
In a sandwich ELISA, the plate is coated with a capture antibody. This format is used to detect:
Answer: D — Antigen in the patient's sample
The antigen is 'sandwiched' between the capture antibody and an enzyme-labelled detection antibody. An example is HBsAg testing.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Latex agglutination tests work by:
Answer: A — Coating latex beads with antigen or antibody, which clump when the matching partner is present
Visible clumping is a positive result; no agglutination is negative. Examples are RF, CRP and ASO latex tests.
Reference: Turgeon: Immunology & Serology in Laboratory Medicine
The reference screening method for antinuclear antibodies (ANA) is:
Answer: B — Indirect immunofluorescence on HEp-2 cells
The pattern seen (homogeneous, speckled, centromere, nucleolar) gives clues to the specific antibody, which is then confirmed by specific assays.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Serum protein electrophoresis shows a suspected monoclonal band. Which test identifies its heavy and light chain type?
Answer: C — Immunofixation electrophoresis
Immunofixation uses specific antisera (anti-IgG, IgA, IgM, kappa, lambda) to identify the monoclonal protein.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Diffusion of antigen and antibody through agar to form a precipitin line is called:
Answer: D — Immunodiffusion
Examples are Ouchterlony double diffusion and radial immunodiffusion (RID).
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which antibodies are most specific for systemic lupus erythematosus (SLE)?
Answer: A — Anti-dsDNA and anti-Smith (anti-Sm)
ANA is sensitive but not specific. Anti-dsDNA also tracks disease activity (especially nephritis). Anti-smooth muscle antibodies (ASMA) are linked to autoimmune hepatitis, not SLE.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which test is the most specific for rheumatoid arthritis?
Answer: B — Anti-CCP (anti-citrullinated protein) antibodies
RF is an antibody (usually IgM) against the Fc region of IgG and also occurs in other conditions and in older people. Anti-CCP is much more specific.
Reference: 2010 ACR/EULAR Rheumatoid Arthritis Classification Criteria
Anti-centromere antibodies are most characteristic of:
Answer: C — Limited cutaneous systemic sclerosis (CREST syndrome)
Anti-Scl-70 (topoisomerase I) is linked to diffuse systemic sclerosis.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Anti-SSA (Ro) and anti-SSB (La) antibodies are typical of:
Answer: D — Sjogren syndrome
Anti-SSA in pregnancy is also linked to neonatal lupus and congenital heart block.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
High anti-thyroid peroxidase (anti-TPO) antibodies most commonly indicate:
Answer: A — Hashimoto thyroiditis
Anti-TPO is the typical marker of autoimmune (Hashimoto) thyroiditis; TSH receptor antibodies indicate Graves disease.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
A raised anti-streptolysin O (ASO) titer supports a recent infection with:
Answer: B — Group A Streptococcus
It supports the diagnosis of post-streptococcal disease such as rheumatic fever or glomerulonephritis. Anti-DNase B is useful after skin infections.
Reference: Turgeon: Immunology & Serology in Laboratory Medicine
Antimitochondrial antibodies (AMA) are characteristic of:
Answer: C — Primary biliary cholangitis
Autoimmune hepatitis type 1 is associated with ANA and anti-smooth muscle antibodies.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
RPR and VDRL are examples of:
Answer: D — Non-treponemal tests
Non-treponemal tests detect antibodies to cardiolipin-lecithin-cholesterol antigen. They are quantitative and used to monitor treatment.
Reference: CDC Sexually Transmitted Infections Treatment Guidelines (2021)
Which test is a treponemal (specific) test for syphilis?
Answer: A — TPPA or FTA-ABS
Treponemal tests (TPPA, TPHA, FTA-ABS, EIA/CIA) usually stay positive for life, so they are not used to monitor treatment.
Reference: CDC Sexually Transmitted Infections Treatment Guidelines (2021)
After treatment for syphilis, response is monitored by:
Answer: B — Quantitative RPR or VDRL titers
A fourfold (two-dilution) fall in non-treponemal titer indicates an adequate response. The same test type should be used each time.
Reference: CDC Sexually Transmitted Infections Treatment Guidelines (2021)
A positive RPR with a negative treponemal test (TPPA) most likely indicates:
Answer: C — A biological false-positive RPR
False-positive non-treponemal results occur in pregnancy, autoimmune disease (e.g., SLE), injecting drug use and some infections.
Reference: CDC Sexually Transmitted Infections Treatment Guidelines (2021)
Treponema pallidum in a primary chancre can be seen directly by:
Answer: D — Dark-field microscopy
T. pallidum is too thin to see on Gram stain. Dark-field microscopy shows motile spirochetes in fresh exudate.
Reference: CDC Sexually Transmitted Infections Treatment Guidelines (2021)
The recommended initial HIV screening test in the laboratory is:
Answer: A — HIV-1/2 antigen/antibody combination immunoassay (4th generation)
It detects p24 antigen and antibodies, shortening the window period. Reactive results go to an HIV-1/HIV-2 antibody differentiation assay, and then HIV RNA if needed.
Reference: CDC: Laboratory Testing for the Diagnosis of HIV Infection - Updated Recommendations (2014)
In the current CDC algorithm, the Western blot as the confirmatory test has been replaced by:
Answer: B — An HIV-1/HIV-2 antibody differentiation immunoassay, followed by HIV-1 RNA (NAT) if needed
The Western blot is less sensitive in early infection and can miss HIV-2.
Reference: CDC: Laboratory Testing for the Diagnosis of HIV Infection - Updated Recommendations (2014)
Which tests monitor HIV treatment and disease progression?
Answer: C — HIV viral load (RNA) and CD4 count
Viral load shows how well antiretroviral therapy suppresses the virus; CD4 count shows immune status.
Reference: CDC: Laboratory Testing for the Diagnosis of HIV Infection - Updated Recommendations (2014)
An HIV-positive patient has a CD4 count of 120 cells/uL. This means:
Answer: D — A high risk of opportunistic infections (AIDS-defining level below 200)
A CD4 count below 200 cells/uL defines AIDS and calls for prophylaxis against infections such as Pneumocystis.
Reference: CDC: Laboratory Testing for the Diagnosis of HIV Infection - Updated Recommendations (2014)
Which test diagnoses HIV in an infant born to an HIV-positive mother?
Answer: A — HIV nucleic acid test (NAT)
Maternal IgG antibodies cross the placenta and can persist for up to 18 months, so infant antibody tests are unreliable.
Reference: CDC: Laboratory Testing for the Diagnosis of HIV Infection - Updated Recommendations (2014)
The first serological marker to appear in acute hepatitis B infection is:
Answer: B — HBsAg
HBsAg appears before symptoms. Anti-HBc IgM follows and is the marker of acute infection.
Reference: CDC: Interpretation of Hepatitis B Serologic Test Results
Which marker indicates high viral replication and high infectivity in hepatitis B?
Answer: C — HBeAg
HBeAg (e antigen) correlates with active replication. HBsAg is the surface (envelope) antigen. HBV DNA quantifies viral load.
Reference: CDC: Interpretation of Hepatitis B Serologic Test Results
HBsAg positive and anti-HBc IgM positive indicate:
Answer: D — Acute hepatitis B infection
HBsAg positive with IgM anti-HBc indicates acute infection. HBsAg positive with total anti-HBc but negative IgM anti-HBc suggests chronic infection.
Reference: CDC: Interpretation of Hepatitis B Serologic Test Results
A person vaccinated against hepatitis B (never infected) has which pattern?
Answer: A — Anti-HBs positive, anti-HBc negative
The vaccine contains only HBsAg, so only anti-HBs develops. Anti-HBs plus anti-HBc indicates immunity from past natural infection.
Reference: CDC: Interpretation of Hepatitis B Serologic Test Results
Infants born to HBsAg-positive mothers should be tested after completing vaccination with:
Answer: B — HBsAg and anti-HBs
Testing at 9-12 months shows whether the infant was infected (HBsAg) or is protected (anti-HBs). Anti-HBc is not used because maternal antibody may persist.
Reference: CDC: Interpretation of Hepatitis B Serologic Test Results
After a reactive anti-HCV screening test, the next test to confirm current infection is:
Answer: C — HCV RNA by NAT (RT-PCR)
RIBA is no longer available. A positive HCV RNA confirms current infection; a negative result suggests past, resolved infection or a false-positive screen.
Reference: CDC: Testing for HCV Infection - Guidance for Clinicians and Laboratorians
A teenager has fever, sore throat and lymphadenopathy with many reactive lymphocytes. The best first test is:
Answer: D — Heterophile antibody (monospot) test
This suggests infectious mononucleosis from EBV. The reactive lymphocytes are mainly activated T cells responding to infected B cells. EBV-specific antibodies (VCA IgM/IgG, EBNA) help if the monospot is negative.
Reference: Turgeon: Immunology & Serology in Laboratory Medicine
A newborn with cataracts and a heart murmur has rubella-specific IgM. This indicates:
Answer: A — Congenital rubella infection
IgM does not cross the placenta, so IgM in the newborn was made by the infant. Rubella IgG in the newborn may simply be maternal.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
A woman's pre-pregnancy check shows rubella IgG positive and IgM negative. This means:
Answer: B — Immunity from past infection or vaccination
Rubella IgG indicates protection. IgM would suggest recent infection.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Lyme disease serology is performed as:
Answer: C — A two-tier approach: sensitive EIA first, then immunoblot or a second EIA
Two-tier testing increases specificity. Serology may be negative in early disease (erythema migrans), which is diagnosed clinically.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
C-reactive protein (CRP) is:
Answer: D — An acute-phase protein that rises within hours of inflammation or infection
CRP is made by the liver in response to IL-6. It is non-specific but useful for monitoring inflammation and treatment response.
Reference: Turgeon: Immunology & Serology in Laboratory Medicine
The confirmatory test for MERS-CoV or SARS-CoV-2 infection is:
Answer: A — RT-PCR on a respiratory specimen
D-dimer and CRP may be raised in severe COVID-19 and help assess severity, but they do not diagnose the infection.
Reference: Turgeon: Immunology & Serology in Laboratory Medicine
Acute cellular rejection of a kidney transplant is mainly caused by:
Answer: B — Recipient T lymphocytes
Recipient T cells recognize donor HLA. Hyperacute rejection is caused by preformed recipient antibodies (for example, ABO or anti-HLA).
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Graft-versus-host disease after stem cell transplant is caused by:
Answer: C — Donor T cells attacking recipient tissues
Irradiation of cellular blood products prevents transfusion-associated GVHD in at-risk patients.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
HLA typing for transplantation is currently performed mainly by:
Answer: D — Molecular methods such as PCR-SSO, PCR-SSP or sequencing
Molecular methods give high-resolution typing needed for stem cell transplant matching.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
A baby is born without a thymus (e.g., DiGeorge syndrome). The main defect is in:
Answer: A — T cell development
DiGeorge syndrome (22q11.2 deletion) causes T cell deficiency, hypocalcemia (absent parathyroids) and heart defects.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
A child has recurrent serious infections with catalase-positive organisms. The neutrophil oxidative burst test (DHR flow cytometry or NBT) is abnormal. The diagnosis is:
Answer: B — Chronic granulomatous disease
CGD is caused by defective NADPH oxidase, so neutrophils cannot kill ingested organisms.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
The most common primary immunodeficiency is:
Answer: C — Selective IgA deficiency
Most patients have no symptoms, but some have recurrent sinopulmonary infections or anaphylaxis to blood products containing IgA.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
A newborn protected by maternal IgG has:
Answer: D — Natural passive immunity
Antibodies passed from mother (placenta or breast milk) give natural passive immunity. Vaccination gives artificial active immunity.
Reference: Stevens: Clinical Immunology and Serology - A Laboratory Perspective
Which statement about vaccines given at birth is correct?
Answer: A — BCG and oral polio (live) and hepatitis B (inactivated) are given at birth in many national schedules
Live vaccines are avoided in severely immunocompromised infants, but routine live vaccines such as BCG are given at birth in many countries, including Pakistan.
Reference: WHO immunization position papers (BCG, hepatitis B, polio)