3.4 Immunology and Serology: Autoimmune Diseases

What is a general definition for autoimmunity?

A. Increase of tolerance to self antigens

B. Loss of tolerance to self-antigens

C. Increase in clonal deletion of mutant cells

D. Manifestation of immunosuppression

B. Loss of tolerance to self-antigens

B Autoimmunity is a loss of tolerance to self-antigens and the subsequent formation of autoantibodies.

An antinuclear antibody test is performed on a specimen from a 55-year-old woman who has unexplained joint pain. The IFA result is a titer of 40 and a homogeneous pattern. The appropriate follow-up for this patient is:

A. Anti-DNA assay

B. Extractable nuclear antigen (ENA) testing

C. Retest ANA in 3-6 months

D. CH50 complement assay

C. Retest ANA in 3-6 months

C Approximately 25% of women in this age range may have low titer-positive ANA assays with no demonstrable connective tissue disease. A patient with anti-DNA positive SLE would be expected to have a much higher titer (> 160) in an IFA assay. A similar titer would be expected for an ENA positive specimen, although the pattern would be speckled. Complement testing would not be indicated with this low titer in a 55-year-old female

Which disease is likely to show a rim (peripheral) pattern in an immunofluorescence (IF) microscopy test for ANA?

A. Mixed connective tissue disease (MCTD)

B. Rheumatoid arthritis

C. Systemic lupus erythematosus

D. Scleroderma

C. Systemic lupus erythematosus

C The rim or peripheral pattern seen in indirect immunofluorescence techniques is most commonly found in cases of active SLE. The responsible autoantibody is highly correlated to anti-double stranded DNA (anti-dsDNA)

A patient's specimen is strongly positive in an ANA ELISA. Which of the following would not be an appropriate follow up to this result?

A. Immunofluorescence test on HEp-2 cells

B. Specific ENA ELISA tests

C. Specific anti-DNA ELISA

D. Rheumatoid factor assay

D. Rheumatoid factor assay

D The ANA ELISA is a screening assay. A positive result may be followed up by more specific antibody ELISA tests or an ANA immunofluorescence test to determine pattern and titer. The ANA ELISA does not screen for rheumatoid factor.

What type of antibodies is represented by the solid or homogeneous pattern in the immunofluorescence test for antinuclear antibodies?

A. Antihistone antibodies

B. Anticentromere antibodies

C. Anti-ENA (anti-Sm and anti-RNP) antibodies

D. Anti-RNA antibodies

A. Antihistone antibodies

A Antihistone antibodies (and also anti-DNA antibodies) cause the solid or homogeneous pattern, which is commonly found in patients with SLE, RA, mixed connective tissue disease, and Sjögren's syndrome. Antibodies to the centromere of chromosomes is a marker for the CREST (calcinosis, Raynaud's phenomenon, esophageal dysfunction, sclerodactyly, and telangiectasia) form of systemic sclerosis.

What disease is indicated by a high titer of anti-Sm (anti-Smith) antibody?

A. Mixed connective tissue disease (MCTD)

B. RA

C. SLE

D. Scleroderma

C. SLE

C High titer anti-Sm is indicative of SLE. Anti-Sm is one of two antibodies against saline extractable nuclear antigens, the other being anti-RNP. These antibodies cause a speckled pattern of immunofluorescence

Which disease is least likely when a nucleolar pattern occurs in an immunofluorescence test for antinuclear antibodies?

A. MCTD

B. Sjögren's syndrome

C. SLE

D. Scleroderma

A. MCTD

A All of the diseases except MCTD may cause a nucleolar pattern of immunofluorescence. Nucleolar fluorescence is caused by anti-RNA antibodies and is seen in about 50% of patients with scleroderma

What antibodies are represented by the nucleolar pattern in the immunofluorescence test for antinuclear antibodies?

A. Antihistone antibodies

B. Anti-dsDNA antibodies

C. Anti-ENA (anti-Sm and anti-RNP) antibodies

D. Anti-RNA antibodies

D. Anti-RNA antibodies

D Anti-RNA antibodies are represented by the nucleolar pattern. This pattern may be seen in most systemic autoimmune diseases and is especially common in patients with scleroderma. Anti-RNA and anti-Sm are not usually found in patients with mixed connective tissue disease. This is a syndrome involving aspects of SLE, RA, scleroderma, and polymyositis. The immunofluorescence pattern most often seen in MCTD is the speckled pattern caused by anti-RNP.

Which test would best distinguish between SLE and MCTD?

A. Multiplex or ELISA test for anti SM and anti-RNP

B. Immunofluorescence testing using Crithidia as substrate

C. Slide agglutination testing

D. Laboratory tests cannot distinguish between these disorders

A. Multiplex or ELISA test for anti-SM and anti-RNP

A The Ouchterlony (double) immunodiffusion assay may be used to identify and differentiate anti-Sm from anti-RNP. Multiplex and ELISA assays, using purified or recombinant antigens, are also available for this testing. Anti-Sm with or without anti-RNP is found in approximately one third of SLE patients. Anti-RNP in the absence of anti-Sm is found in over 95% of MCTD patients.

An ANA test on HEp-2 cells shows nucleolar staining in interphase cells and dense chromatin staining in mitotic cells. The most likely cause of this staining pattern is:

A. Antifibrillarin antibody

B. Antiribosomal p antibody

C. A serum with nucleolar and homogeneous patterns

D. Technical artifact

A. Antifibrillarin antibody

A Antifibrillarin antibody has this appearance. Ribosomal p antibody has nucleolar staining and a background homogeneous and cytoplasmic stain. A combination nucleolar/homogeneous specimen will also show homogeneous staining in the interphase cells. This pattern is not seen in typical technical artifacts.

Which immunofluorescence pattern indicates the need for ENA testing by Ouchterlony immunodiffusion, Multiplex, or ELISA assays?

A. Homogeneous or solid

B. Peripheral or rim

C. Speckled

D. Nucleolar

C. Speckled

C A speckled pattern is often due to the presence of antibodies against the extractable nuclear antigens, such as Sm, RNP, SSA, and SSB. Homogenous and rim patterns suggest antibodies to double-stranded DNA. The homogeneous pattern may also be seen with antibodies to deoxyribonuclear protein, which is not an ENA. Nucleolar patterns often indicate antibodies to RNA or fibrillarin.

Which of the following is used in rapid slide tests for detection of rheumatoid factors?

A. Whole IgM molecules

B. Fc portion of the IgG molecule

C. Fab portion of the IgG molecule

D. Fc portion of the IgM molecule

B. Fc portion of the IgG molecule

B. Rheumatoid factors react with the Fc portion of the IgG molecule and are usually IgM. This is the basis of rapid agglutination tests for RA. Particles of latex or cells are coated with IgG. Addition of serum containing rheumatoid factor results in visible agglutination.

Which of the following methods is least likely to give a definitive result for the diagnosis of RA?

A. Nephelometric measurement of anti-IgG

B. Agglutination testing for rheumatoid factor

C. Anti CCP

D. Immunofluorescence testing for antinuclear antibodies

D. Immunofluorescence testing for antinuclear antibodies

D Patients with RA often show a homogeneous pattern of fluorescence in tests for antinuclear antibodies. However, this pattern is seen in a wide range of systemic autoimmune diseases and in many normal persons at a titer below 10. The first two methods listed may be used to identify anti-IgG, which is required to establish a diagnosis of RA Anti CCP is a specific assay for rheumatoid arthritis.

Which disease might be indicated by antibodies to smooth muscle?

A. Atrophic gastritis

B. Autoimmune hepatitis

C. Myasthenia gravis

D. Sjögren's syndrome

B. Autoimmune hepatitis

B Antibodies to smooth muscle are found in the serum of up to 70% of patients with active chronic hepatitis and up to 50% of patients with primary biliary cirrhosis.

Antibodies to thyroid peroxidase can be detected by using agglutination assays. Which of the following diseases may show positive results with this type of assay?

A. Graves' disease and Hashimoto's thyroiditis

B. Myasthenia gravis

C. Granulomatous thyroid disease

D. Addison's disease

A. Graves' disease and Hashimoto's thyroiditis

A Antibodies to thyroid peroxidase may be detected in both Graves' disease (hyperthyroidism) and Hashimoto's thyroiditis (hypothyroidism). If a positive result is found to thyroid peroxidase, thyroxine levels can be measured to distinguish between the two diseases.

What is the main use of laboratory tests to detect antibodies to islet cells and insulin in cases of insulin-dependent diabetes mellitus (IDDM)?

A. To regulate levels of injected insulin

B. To diagnose IDDM

C. To rule out the presence of other autoimmune diseases

D. To screen susceptible individuals prior to destruction of β cells

D. To screen susceptible individuals prior to destruction of β cells

D Fasting hyperglycemia is the primary finding used to diagnose IDDM. For individuals with an inherited susceptibility to the development of IDDM, laboratory tests for the detection of antibodies to islet cells and insulin may help to initiate early treatment before complete destruction of β cells.

A patient presents with clinical symptoms of celiac disease. Tests for anti-tissue transglutaminase and antigliadin antibodies are negative. Which of the following tests should be ordered?

A. IgG level

B. HLA DQ typing

C. HLA DR typing

D. IgM level

B. HLA DQ typing

B While antibodies to tissue transglutaminase and gliadin are often found in celiac disease, their combined sensitivity is less than 100%. Celiac disease is almost exclusively associated with the presence of HLA DQ2 and/or HLA DQ8. These HLA genes are not diagnostic of celiac disease, but provide a testing alternative in antibody-negative individuals who meet the clinical diagnostic criteria for celiac disease.

A specimen appears to have a perinuclear staining pattern in an antineutrophil cytoplasmic antibody (ANCA) immunofluorescent assay using ethanolfixed neutrophils, suggesting the possibility of a pANCA. On which of the following substrates would this specimen display cytoplasmic speckling?

A. Formalin-fixed neutrophils

B. Unfixed neutrophils

C. HEp-2 cells

D. Rabbit kidney tissue

A. Formalin-fixed neutrophils

A Antibodies to neutrophil cytoplasmic antigen demonstrating a perinuclear pattern of fluorescence indicate a diagnosis of vasculitis. However, atypical ANCAs and ANAs also demonstrate a perinuclear staining pattern on ethanol fixed neutrophils. To differentiate these from pANCA, specimens appearing as a pANCA on ethanol-fixed cells are tested on formalin-fixed neutrophils. The myeloperoxidase containing granules that coalesce around the nuclear membrane during ethanol fixation will remain in the cytoplasm during formalin fixation. Thus, pANCA will have a cytoplasmic (cANCA) pattern on a formalin-fixed slide, but ANAs will retain a perinuclear pattern and the fluorescence will be diminished.