MLT GlobeImmunology & Serology: Autoimmune & hypersensitivity – page 3
80 Immunology & Serology MCQs on Autoimmune & hypersensitivity with answers and explanations.
On an indirect immunofluorescence ANA test using HEp-2 cells, the entire interphase nucleus stains evenly. This homogeneous pattern is most associated with antibodies to:
A homogeneous (diffuse) nuclear pattern reflects anti-dsDNA/anti-histone/nucleosome antibodies, seen in SLE and drug-induced lupus. Centromere gives discrete speckles; mitochondria stain cytoplasm.
Allergen immunotherapy (desensitisation) is thought to work partly by inducing an antibody that intercepts allergen before it reaches mast-cell IgE. Which class is this?
Repeated allergen doses shift the response toward allergen-specific IgG, mainly IgG4, which binds allergen and prevents IgE cross-linking on mast cells.
A renal biopsy from a patient with immune-complex (type III) glomerulonephritis is examined by immunofluorescence. Which finding is expected?
Circulating immune complexes lodge irregularly, giving a granular 'lumpy-bumpy' pattern. Linear IgG suggests anti-GBM (type II) disease; sensitised T cells indicate type IV.
In type II (cytotoxic) hypersensitivity, what event starts the tissue damage?
Type II injury begins when IgG or IgM binds antigens on cells or tissue, triggering complement lysis, opsonisation or ADCC. Mast-cell IgE is type I; circulating complexes are type III.
Which autoantibody is most specific for systemic lupus erythematosus?
ANA is very sensitive for SLE but not specific. Anti-dsDNA and anti-Sm are highly specific, and anti-dsDNA levels follow lupus nephritis activity. Anti-histone suggests drug-induced lupus.
Compared with rheumatoid factor, anti-CCP antibody in rheumatoid arthritis is:
Anti-cyclic citrullinated peptide antibodies are about 95% specific for RA and may appear years before symptoms. RF (IgM against the Fc of IgG) also occurs in infections and other autoimmune diseases.
A HEp-2 indirect immunofluorescence ANA shows discrete speckles (about 40–80 per interphase nucleus) that align on the chromosomes of metaphase cells. The associated antibody is:
The discrete speckled (centromere) pattern shows countable dots that line up on chromosomes in metaphase cells. It is associated with limited cutaneous systemic sclerosis (CREST).
A homogeneous ANA pattern with staining of the condensed chromosomes in mitotic cells is most associated with antibodies to:
Homogeneous nuclear staining with positive metaphase chromatin is typical of antibodies to dsDNA, histones and nucleosomes. SS-A and U1-RNP give speckled patterns with negative metaphase chromatin.
A patient with a positive ANA has high-titre anti-U1-RNP as the only specific autoantibody, Raynaud phenomenon and swollen hands. The most likely diagnosis is:
A high titre of anti-U1-RNP is a defining feature of mixed connective tissue disease. Drug-induced lupus is associated with anti-histone antibodies.
Anti-SS-A (Ro) antibodies in a pregnant woman carry a risk of which condition in the newborn?
Maternal IgG anti-Ro/SS-A crosses the placenta and can damage the fetal cardiac conduction system, causing congenital heart block and neonatal lupus rash.
A patient with myositis, interstitial lung disease and 'mechanic's hands' most likely has which antibody?
Anti-Jo-1 (histidyl-tRNA synthetase) defines the antisynthetase syndrome: myositis, interstitial lung disease, arthritis and mechanic's hands. Its ANA pattern is cytoplasmic.
On ethanol-fixed neutrophils, a perinuclear (p-ANCA) immunofluorescence pattern most often corresponds to antibodies against:
p-ANCA usually reflects anti-myeloperoxidase, seen in microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis. c-ANCA with anti-proteinase 3 is typical of granulomatosis with polyangiitis.
The preferred initial serologic screening test for celiac disease in a patient with normal total IgA is:
IgA anti-tTG is sensitive and specific and is the recommended first test. Total IgA should be checked because IgA deficiency causes false-negative IgA-based tests.
Post-streptococcal glomerulonephritis with granular deposits and low C3 is an example of which hypersensitivity type?
Circulating immune complexes deposit in glomeruli and activate complement, giving a lumpy-bumpy granular pattern and low C3. This is type III (immune complex) hypersensitivity.
Goodpasture (anti-GBM) disease shows linear IgG staining along the glomerular basement membrane. This is classified as:
Antibody binding directly to a fixed tissue antigen (type IV collagen) is type II hypersensitivity and gives linear staining. Immune complex disease (type III) gives granular staining.
A patient develops fever, rash, arthralgia and proteinuria 8–10 days after receiving antivenom made in horses. The most likely mechanism is:
Serum sickness is a type III reaction: antibodies to foreign serum proteins form immune complexes about 1–2 weeks after exposure. Anaphylaxis would occur within minutes.
In an indirect immunofluorescence test using the flagellate Crithidia luciliae, fluorescence of the kinetoplast indicates antibodies to:
The kinetoplast of Crithidia luciliae contains circular double-stranded DNA free of histones, so its staining is highly specific for anti-dsDNA. Anti-histone antibodies would not stain it because no histones are present.
A 50-year-old man has chronic sinusitis, lung nodules and glomerulonephritis. Neutrophil IIF shows diffuse granular cytoplasmic staining (c-ANCA). The target antigen and likely diagnosis are:
The c-ANCA pattern corresponds mainly to anti-PR3, which is strongly associated with granulomatosis with polyangiitis (upper airway, lung, kidney). MPO antibodies give a p-ANCA pattern and suggest microscopic polyangiitis.
In suspected pernicious anaemia, which autoantibody is the most specific for the diagnosis?
Anti-intrinsic factor antibody is highly specific for pernicious anaemia, though only moderately sensitive. Anti-parietal cell antibody is more sensitive but less specific, being found in atrophic gastritis and some healthy older adults.
A HEp-2 ANA shows bright staining of the nucleoli with little nucleoplasm staining. This pattern is most associated with:
A nucleolar ANA pattern (e.g., anti-PM/Scl, anti-fibrillarin, anti-Th/To) is typical of systemic sclerosis. Drug-induced lupus usually shows a homogeneous pattern from anti-histone antibodies.